Merge and label stdout/stderr for FileCheck (#2283)

Adds a simple script to merge stdout/stderr and put on labels. This is hidden to the RUN line using lit.cfg.py.

This is my solution to addressing how errors printed by the toolchain break sorting of stdout output; just put stdout first. We could also have toggles for interleaving output or such, which might help test whether we do it properly.

This also moves some previous-distributed replacement logic into lit_autoupdate_base.py: I think having that adjacent to lit.cfg.py is probably the better choice, and it reduces duplication in toolchain scripts. It happens here because I need to change the resulting commands to include the merge.

bazel/testing/BUILD

@@ -2,4 +2,11 @@
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-exports_files(["lit_test.py"])
+package(default_visibility=["//visibility:public"])
+
+exports_files(["lit_test.py", "merge_output.py"])
+
+py_binary(
+  name = "merge_output",
+  srcs = ["merge_output.py"],
+)

bazel/testing/lit.cfg.py

@@ -20,13 +20,16 @@ config.name = "lit"
 config.suffixes = [".carbon"]
 config.test_format = lit.formats.ShTest()
 
+_MERGE_OUTPUT = fullpath("carbon/bazel/testing/merge_output")
+
 config.substitutions.append(
     (
         "%{carbon}",
-        fullpath("carbon/toolchain/driver/carbon"),
+        "%s %s" % (_MERGE_OUTPUT, fullpath("carbon/toolchain/driver/carbon")),
     )
 )
-_EXPLORER = "%s --prelude=%s" % (
+_EXPLORER = "%s %s --prelude=%s" % (
+    _MERGE_OUTPUT,
     fullpath("carbon/explorer/explorer"),
     fullpath("carbon/explorer/data/prelude.carbon"),
 )

bazel/testing/lit_autoupdate_base.py

@@ -23,11 +23,17 @@ AUTOUPDATE_MARKER = "// AUTOUPDATE: "
 # Indicates no autoupdate is requested.
 NOAUTOUPDATE_MARKER = "// NOAUTOUPDATE"
 
+# Standard replacements normally done in lit.cfg.py.
+MERGE_OUTPUT = "./bazel-bin/bazel/testing/merge_output"
+LIT_REPLACEMENTS = [
+    ("%{carbon}", f"{MERGE_OUTPUT} ./bazel-bin/toolchain/driver/carbon"),
+    ("%{explorer}", f"{MERGE_OUTPUT} ./bazel-bin/explorer/explorer"),
+]
+
 
 class ParsedArgs(NamedTuple):
     build_mode: str
     build_target: str
-    cmd_replace: Tuple[str, str]
     extra_check_replacements: List[Tuple[Pattern, Pattern, str]]
     line_number_format: str
     line_number_pattern: Pattern
@@ -51,14 +57,6 @@ def parse_args() -> ParsedArgs:
         required=True,
         help="The target to build.",
     )
-    parser.add_argument(
-        "--cmd_replace",
-        nargs=2,
-        metavar=("BEFORE", "AFTER"),
-        required=True,
-        help="Adds a command replacement of `BEFORE` with `AFTER`. Typically "
-        "`BEFORE` will look like `%{name}`",
-    )
     parser.add_argument(
         "--extra_check_replacement",
         nargs=3,
@@ -96,7 +94,6 @@ def parse_args() -> ParsedArgs:
     return ParsedArgs(
         build_mode=parsed_args.build_mode,
         build_target=parsed_args.build_target,
-        cmd_replace=parsed_args.cmd_replace,
         extra_check_replacements=extra_check_replacements,
         line_number_format=parsed_args.line_number_format,
         line_number_pattern=re.compile(parsed_args.line_number_pattern),
@@ -230,7 +227,7 @@ def get_matchable_test_output(
     # Mirror lit.cfg.py substitutions; bazel runs don't need --prelude.
     # Also replaces `%s` with the test file.
     autoupdate_cmd = replace_all(
-        autoupdate_cmd, [parsed_args.cmd_replace, ("%s", test)]
+        autoupdate_cmd, [("%s", test)] + LIT_REPLACEMENTS
     )
 
     # Run the autoupdate command to generate output.
@@ -404,6 +401,7 @@ def main() -> None:
             "build",
             "-c",
             parsed_args.build_mode,
+            "//bazel/testing:merge_output",
             parsed_args.build_target,
         ]
     )

bazel/testing/lit_test.py

@@ -9,6 +9,7 @@ SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 import argparse
 import os
 from pathlib import Path
+import shutil
 import subprocess
 
 
@@ -33,9 +34,16 @@ def main():
         "-v",
     ]
 
-    # Force tests to be explicit about command paths.
+    # Force tests to be explicit about command paths. Some tools are required by
+    # bazel's py_binary output in order to find python3, so we add these. The
+    # list of tools may prove to be fragile: if so, we may need to change or
+    # remove the PATH hiding.
+    system_tools = Path(os.environ["TEST_TMPDIR"]).joinpath("system_tools")
+    system_tools.mkdir()
+    for tool in ("env", "grep", "python3", "sh", "which"):
+        system_tools.joinpath(tool).symlink_to(shutil.which(tool))
     env = os.environ.copy()
-    del env["PATH"]
+    env["PATH"] = str(system_tools)
 
     # Run lit.
     try:

bazel/testing/merge_output.py

@@ -0,0 +1,29 @@
+"""Merges stdout and stderr into a single stream with labels."""
+
+__copyright__ = """
+Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+Exceptions. See /LICENSE for license information.
+SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+"""
+
+import subprocess
+import sys
+import textwrap
+
+
+def main() -> None:
+    p = subprocess.run(
+        sys.argv[1:],
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        encoding="utf-8",
+    )
+    if p.stdout:
+        print(textwrap.indent(p.stdout, "STDOUT: "), end="")
+    if p.stderr:
+        print(textwrap.indent(p.stderr, "STDERR: "), end="")
+    exit(p.returncode)
+
+
+if __name__ == "__main__":
+    main()

explorer/README.md

@@ -72,8 +72,8 @@ boilerplate at the top:
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 // CHECK:result: 0
 

explorer/lit_autoupdate.py

@@ -25,9 +25,6 @@ def main() -> None:
         # Flags to configure for explorer testing.
         "--build_target",
         "//explorer",
-        "--cmd_replace",
-        "%{explorer}",
-        "./bazel-bin/explorer/explorer",
         "--testdata",
         "explorer/testdata",
         "--line_number_pattern",

explorer/testdata/BUILD

@@ -6,6 +6,7 @@ load("//bazel/testing:lit.bzl", "glob_lit_tests")
 
 glob_lit_tests(
     data = [
+        "//bazel/testing:merge_output",
         "//explorer",
         "@llvm-project//llvm:FileCheck",
         "@llvm-project//llvm:not",

explorer/testdata/addr/fail_method_let.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -26,7 +26,7 @@ class Point {
 
 fn Main() -> i32 {
   let p: Point = Point.Origin();
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_let.carbon:[[@LINE+1]]: method GetSetX requires its receiver to be an lvalue
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_let.carbon:[[@LINE+1]]: method GetSetX requires its receiver to be an lvalue
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;

explorer/testdata/addr/fail_method_me_misspelled.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 class C {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_misspelled.carbon:[[@LINE+1]]: illegal binding pattern in implicit parameter list
   fn F[addr mew: Self*]() {}
 }
 

explorer/testdata/addr/fail_method_me_type.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -30,7 +30,7 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = Point.Origin();
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_type.carbon:[[@LINE+1]]: type error in method access, receiver type: 'class Point' is not implicitly convertible to 'class Shape'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/addr/fail_method_me_type.carbon:[[@LINE+1]]: type error in method access, receiver type: 'class Point' is not implicitly convertible to 'class Shape'
   var x: auto = p.GetSetX(42);
   if (p.x == 42) {
     return x;

explorer/testdata/addr/method.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/addr/nested_method.carbon

@@ -3,10 +3,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/alias/class_alias.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:b.n: 1
-// CHECK:d.Get(0): 2
-// CHECK:e.Get(1): 3
-// CHECK:result: 0
+// CHECK:STDOUT: b.n: 1
+// CHECK:STDOUT: d.Get(0): 2
+// CHECK:STDOUT: e.Get(1): 3
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/alias/fail_alias_expression.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_expression.carbon:[[@LINE+1]]: invalid target for alias declaration
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_expression.carbon:[[@LINE+1]]: invalid target for alias declaration
 alias A = 5;
 
 fn Main() -> i32 { return 0; }

explorer/testdata/alias/fail_alias_var.carbon

@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 var v: i32;
 // TODO: This should probably be valid if we allow global variables at all.
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_var.carbon:[[@LINE+1]]: invalid target for alias declaration
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_alias_var.carbon:[[@LINE+1]]: invalid target for alias declaration
 alias A = v;
 
 fn Main() -> i32 { return 0; }

explorer/testdata/alias/fail_self_alias.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_self_alias.carbon:[[@LINE+1]]: 'a' is not usable until after it has been completely declared
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/alias/fail_self_alias.carbon:[[@LINE+1]]: 'a' is not usable until after it has been completely declared
 alias a = a;
 
 fn Main() -> i32 {

explorer/testdata/alias/function_alias.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 7
+// CHECK:STDOUT: result: 7
 
 package ExplorerTest api;
 

explorer/testdata/alias/interface_alias.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 12345
+// CHECK:STDOUT: result: 12345
 
 package ExplorerTest api;
 

explorer/testdata/alias/member_name_alias.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/alias/struct_alias.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:ab.a: 2
-// CHECK:ab.b: 1
-// CHECK:ba.a: 2
-// CHECK:ba.b: 1
-// CHECK:result: 0
+// CHECK:STDOUT: ab.a: 2
+// CHECK:STDOUT: ab.b: 1
+// CHECK:STDOUT: ba.a: 2
+// CHECK:STDOUT: ba.b: 1
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/alias/type_alias.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 4
+// CHECK:STDOUT: result: 4
 
 package ExplorerTest api;
 

explorer/testdata/array/fail_index.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   var x: [i32; 2] = (0, 1);
-  // CHECK:RUNTIME ERROR: {{.*}}/explorer/testdata/array/fail_index.carbon:[[@LINE+1]]: index 2 out of range in (0, 1)
+  // CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/testdata/array/fail_index.carbon:[[@LINE+1]]: index 2 out of range in (0, 1)
   return x[2];
 }

explorer/testdata/array/fail_negative_size.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_negative_size.carbon:[[@LINE+1]]: Array size cannot be negative
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_negative_size.carbon:[[@LINE+1]]: Array size cannot be negative
   var x: [i32; -1] = ();
   return x[0];
 }

explorer/testdata/array/fail_size_mismatch.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_size_mismatch.carbon:[[@LINE+1]]: type error in name binding: '(i32, i32, i32)' is not implicitly convertible to '[i32; 2]'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/array/fail_size_mismatch.carbon:[[@LINE+1]]: type error in name binding: '(i32, i32, i32)' is not implicitly convertible to '[i32; 2]'
   var x: [i32; 2] = (0, 1, 2);
   return x[0];
 }

explorer/testdata/array/index.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/array/nested.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/as/as_same_type.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 5
+// CHECK:STDOUT: result: 5
 
 package ExplorerTest api;
 

explorer/testdata/as/convert.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 5
+// CHECK:STDOUT: result: 5
 
 package ExplorerTest api;
 

explorer/testdata/as/fail_destination_not_type.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_destination_not_type.carbon:[[@LINE+1]]: Expected a type, but got 7
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_destination_not_type.carbon:[[@LINE+1]]: Expected a type, but got 7
   return 4 as 7;
 }

explorer/testdata/as/fail_no_conversion.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -12,7 +12,7 @@ class A { var n: i32; }
 
 fn Main() -> i32 {
   var a: A = {.n = 5};
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_no_conversion.carbon:[[@LINE+2]]: type error in `as`: `class A` is not explicitly convertible to `i32`:
-  // CHECK:could not find implementation of interface As(T = i32) for class A
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/as/fail_no_conversion.carbon:[[@LINE+2]]: type error in `as`: `class A` is not explicitly convertible to `i32`:
+  // CHECK:STDERR: could not find implementation of interface As(T = i32) for class A
   return a as i32;
 }

explorer/testdata/as/implicit_as.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 5
+// CHECK:STDOUT: result: 5
 
 package ExplorerTest api;
 

explorer/testdata/assert/assert.carbon

@@ -5,10 +5,10 @@
 // This won't auto-update because it uses a regex for the prelude line number,
 // so that it doesn't need to be updated on every prelude change.
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // NOAUTOUPDATE
-// CHECK:RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
+// CHECK:STDERR: RUNTIME ERROR: {{.*}}/explorer/data/prelude.carbon:{{.*}}: "HALLO WELT"
 
 package ExplorerTest api;
 

explorer/testdata/assign/convert_rhs.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 1
+// CHECK:STDOUT: result: 1
 
 package ExplorerTest api;
 

explorer/testdata/assign/destruct_original.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/assign/reassign_original.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/assoc_const/fail_anonymous.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface Iface {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/assoc_const/fail_anonymous.carbon:[[@LINE+1]]: syntax error, unexpected UNDERSCORE, expecting identifier
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/assoc_const/fail_anonymous.carbon:[[@LINE+1]]: syntax error, unexpected UNDERSCORE, expecting identifier
   let _:! Type;
 }
 

explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +14,7 @@ interface HasThreeTypes {
   let C:! Type;
 }
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon:[[@LINE+1]]: implementation missing (i32).B; have constraint interface HasThreeTypes where i32 is interface HasThreeTypes and (i32).A == i32 and (i32).C == i32
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_1.carbon:[[@LINE+1]]: implementation missing (i32).B; have constraint interface HasThreeTypes where i32 is interface HasThreeTypes and (i32).A == i32 and (i32).C == i32
 external impl i32 as HasThreeTypes where .A == i32 and .C == i32 {}
 
 fn Main() -> i32 { return 0; }

explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +14,7 @@ interface HasThreeTypes {
   let C:! Type;
 }
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for (i32).B
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_incomplete_impl_2.carbon:[[@LINE+1]]: implementation doesn't provide a concrete value for (i32).B
 external impl i32 as HasThreeTypes where .A == i32 and .B == .C {}
 
 fn Main() -> i32 { return 0; }

explorer/testdata/assoc_const/fail_indirectly_equal.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -23,7 +23,7 @@ fn F2[U:! A where .T == i32](x: i32) -> U.T {
 }
 
 fn F3[T:! A where .T == i32, U:! A where .T == i32](x: T.T) -> U.T {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_indirectly_equal.carbon:[[@LINE+1]]: type error in return value: '(T).T' is not implicitly convertible to '(U).T'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_indirectly_equal.carbon:[[@LINE+1]]: type error in return value: '(T).T' is not implicitly convertible to '(U).T'
   return x;
 }
 

explorer/testdata/assoc_const/fail_match_in_deduction.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 // TODO: Should this work?
@@ -22,7 +22,7 @@ fn F[Scalar:! Type, V:! Vector where .Dim == 3](p: Point(Scalar, V.Dim), v: V) {
 fn G[Scalar:! Type](p: Point(Scalar, 3)) {}
 fn H[V:! Vector where .Dim == 3](v: V) {
   var p: Point(i32, V.Dim) = {};
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-type values, `(V).Dim` != `3`
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_match_in_deduction.carbon:[[@LINE+1]]: mismatch in non-type values, `(V).Dim` != `3`
   G(p);
 }
 

explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -38,7 +38,7 @@ class C(T:! Type) {
 
 external impl C(i32) as B where .TB == () {
   fn FB() -> () { return (); }
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon:[[@LINE+1]]: ambiguous implementations of interface B for class C(T = i32)
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multi_impl_scoping.carbon:[[@LINE+1]]: ambiguous implementations of interface B for class C(T = i32)
 }
 
 fn Main() -> i32 { return C(i32).FB(); }

explorer/testdata/assoc_const/fail_multiple_deduction.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -16,9 +16,9 @@ interface HasThreeTypes {
 }
 fn F[T:! Type](x: (T, T, T));
 fn G[X:! HasThreeTypes where .A == .B and .B == .C and .C == .A](x: X) {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multiple_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
-  // CHECK:  (X).A
-  // CHECK:  (X).B
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_multiple_deduction.carbon:[[@LINE+3]]: deduced multiple different values for T:! Type:
+  // CHECK:STDERR:   (X).A
+  // CHECK:STDERR:   (X).B
   F(x.Make());
 }
 

explorer/testdata/assoc_const/fail_overspecified_impl.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -12,7 +12,7 @@ interface HasType {
   let T:! Type;
 }
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_overspecified_impl.carbon:[[@LINE+1]]: implementation provides multiple values for (i32).T: i32 and {.a: i32}
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_overspecified_impl.carbon:[[@LINE+1]]: implementation provides multiple values for (i32).T: i32 and {.a: i32}
 external impl i32 as HasType where .T == i32 and .T == {.a: i32} {}
 
 fn Main() -> i32 { return 0; }

explorer/testdata/assoc_const/fail_redefined.carbon

@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 interface Iface {
   let T:! Type;
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE-1]]
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE+1]]: Duplicate name `T` also found at {{.*}}/explorer/testdata/assoc_const/fail_redefined.carbon:[[@LINE-1]]
   let T:! Type;
 }
 

explorer/testdata/assoc_const/fail_unknown_value.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -13,7 +13,7 @@ interface Iface { let N:! i32; }
 fn PickType(N: i32) -> Type { return i32; }
 
 fn F[T:! Iface](x: T) -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value.carbon:[[@LINE+1]]: value of associated constant (T).N is not known
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value.carbon:[[@LINE+1]]: value of associated constant (T).N is not known
   var x: PickType(T.N) = 0;
   return x;
 }

explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +14,7 @@ fn PickType(N: i32) -> Type { return i32; }
 
 fn F[T:! Iface where .N == 5](x: T) -> i32 {
   // TODO: This should be valid: the value of T.N is known to be 5 here.
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon:[[@LINE+1]]: value of associated constant (T).N is not known
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/assoc_const/fail_unknown_value_specified_in_constraint.carbon:[[@LINE+1]]: value of associated constant (T).N is not known
   var x: PickType(T.N) = 0;
   return x;
 }

explorer/testdata/assoc_const/impl_lookup.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 1
+// CHECK:STDOUT: result: 1
 
 package ExplorerTest api;
 

explorer/testdata/assoc_const/implement.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 2
+// CHECK:STDOUT: result: 2
 
 package ExplorerTest api;
 

explorer/testdata/assoc_const/lookup_in_rewrite.carbon

@@ -2,19 +2,19 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:1
-// CHECK:i32.Hash
-// CHECK:0
-// CHECK:Potato.(Hashable.Hash)
-// CHECK:1
-// CHECK:Potato.Hash
-// CHECK:2
-// CHECK:Potato.Hash
-// CHECK:2
-// CHECK:result: 0
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: i32.Hash
+// CHECK:STDOUT: 0
+// CHECK:STDOUT: Potato.(Hashable.Hash)
+// CHECK:STDOUT: 1
+// CHECK:STDOUT: Potato.Hash
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: Potato.Hash
+// CHECK:STDOUT: 2
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/assoc_const/member_of_value.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 2
+// CHECK:STDOUT: result: 2
 
 package ExplorerTest api;
 

explorer/testdata/assoc_const/simple_constraint.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 3
+// CHECK:STDOUT: result: 3
 
 package ExplorerTest api;
 

explorer/testdata/assoc_const/simple_equality.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/addition.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 7
+// CHECK:STDOUT: result: 7
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/choice.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/fail_alternative_not_type.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon:[[@LINE+1]]: Expected a type, but got (42)
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_not_type.carbon:[[@LINE+1]]: Expected a type, but got (42)
 choice C { X(42) }
 
 fn Main() -> i32 {

explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 choice Ch {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon:[[@LINE+1]]: 'Ch' is not usable until after it has been completely declared
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_alternative_uses_choice.carbon:[[@LINE+1]]: 'Ch' is not usable until after it has been completely declared
   Opt(Ch)
 }
 

explorer/testdata/basic_syntax/fail_assign_to_function.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -12,7 +12,7 @@ fn F() {}
 fn G() {}
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_function.carbon:[[@LINE+1]]: Cannot assign to rvalue 'F'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_function.carbon:[[@LINE+1]]: Cannot assign to rvalue 'F'
   F = G;
   return 0;
 }

explorer/testdata/basic_syntax/fail_assign_to_rval.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon:[[@LINE+1]]: Cannot assign to rvalue '1'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_assign_to_rval.carbon:[[@LINE+1]]: Cannot assign to rvalue '1'
   1 = 0;
   return 0;
 }

explorer/testdata/basic_syntax/fail_block.carbon

@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   {
-    // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_block.carbon:[[@LINE+1]]: syntax error, unexpected RETURN, expecting PERIOD or RIGHT_CURLY_BRACE
+    // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_block.carbon:[[@LINE+1]]: syntax error, unexpected RETURN, expecting PERIOD or RIGHT_CURLY_BRACE
     return 0;
   }
 }

explorer/testdata/basic_syntax/fail_choice_no_parens.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -17,9 +17,9 @@ choice Ints {
 fn Main() -> i32 {
   match (Ints.None()) {
     case Ints.None => { return 0; }
-    // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
-    // CHECK:expected: fn () -> choice Ints
-    // CHECK:actual: choice Ints
+    // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_choice_no_parens.carbon:[[@LINE+3]]: type error in `match` pattern type
+    // CHECK:STDERR: expected: fn () -> choice Ints
+    // CHECK:STDERR: actual: choice Ints
     default => { return 1; }
   }
 }

explorer/testdata/basic_syntax/fail_invalid_char.carbon

@@ -2,9 +2,9 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
-// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_char.carbon:[[@LINE+1]]: invalid character '\xEF' in source file.
+// CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_char.carbon:[[@LINE+1]]: invalid character '\xEF' in source file.
 �

explorer/testdata/basic_syntax/fail_invalid_integer.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer.carbon:[[@LINE+1]]: Invalid integer literal: 11111111111111111111111111
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer.carbon:[[@LINE+1]]: Invalid integer literal: 11111111111111111111111111
   return 11111111111111111111111111;
 }

explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon:[[@LINE+1]]: Invalid type literal: i11111111111111111111111111
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_integer_type.carbon:[[@LINE+1]]: Invalid type literal: i11111111111111111111111111
   var x: i11111111111111111111111111 = 1;
   return 0;
 }

explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon:[[@LINE+1]]: Expected expression for variable type
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_invalid_var_expression.carbon:[[@LINE+1]]: Expected expression for variable type
 var a: auto;
 
 fn Main() -> i32 { return 0; }

explorer/testdata/basic_syntax/fail_missing_var.carbon

@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
   // error
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_missing_var.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_missing_var.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
   x : i32;
   return 1;
 }

explorer/testdata/basic_syntax/fail_nested_binding.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_nested_binding.carbon:[[@LINE+1]]: The type of a binding pattern cannot contain bindings.
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_nested_binding.carbon:[[@LINE+1]]: The type of a binding pattern cannot contain bindings.
   var x: (T: Type) = 1;
   return 1;
 }

explorer/testdata/basic_syntax/fail_unimplemented_example.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon:[[@LINE+1]]: Unimplemented
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unimplemented_example.carbon:[[@LINE+1]]: Unimplemented
   return 1 __unimplemented_example_infix 2;
 }

explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon:[[@LINE+1]]: Unknown intrinsic 'nonexistent'
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unknown_intrinsic.carbon:[[@LINE+1]]: Unknown intrinsic 'nonexistent'
   return __intrinsic_nonexistent();
 }

explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn Main() -> i32 {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon:[[@LINE+1]]: Only i32 is supported for now: i64
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_unsupported_integer_type.carbon:[[@LINE+1]]: Only i32 is supported for now: i64
   var x: i64 = 1;
   return 0;
 }

explorer/testdata/basic_syntax/fail_var_named_self.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -12,7 +12,7 @@ fn Main() -> i32 {
   // Error: can't use keyword `Self` as the name of a variable.
   // TODO: Current error message is unclear, better would be to say
   // something like: unexpected `Self`, expecting identifier
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_named_self.carbon:[[@LINE+1]]: syntax error, unexpected COLON, expecting SLASH or binary *
   var Self : i32 = 0;
   return Self;
 }

explorer/testdata/basic_syntax/fail_var_type.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -11,7 +11,7 @@ package ExplorerTest api;
 fn Main () -> i32
 {
   // 42 cannot be used as the type of a variable.
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_type.carbon:[[@LINE+1]]: Expected a type, but got 42
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/basic_syntax/fail_var_type.carbon:[[@LINE+1]]: Expected a type, but got 42
   var x: 42 = 0;
   return x;
 }

explorer/testdata/basic_syntax/next.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/not_compare_precedence.carbon

@@ -2,13 +2,13 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 fn CompareBools(a: bool, b: bool) -> bool {
-  // CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/not_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
+  // CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/basic_syntax/not_compare_precedence.carbon:[[@LINE+1]]: syntax error, unexpected EQUAL_EQUAL, expecting SEMICOLON
   return not a == b;
 }

explorer/testdata/basic_syntax/placeholder_variable.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/record.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/star.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/trace.carbon

@@ -2,24 +2,24 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 //
 // A lot of output is elided: this is only checking for a few things for simple
 // sanity checking on --parser_debug --trace_file=- output.
 //
 // NOAUTOUPDATE
-// CHECK:********** source program **********
-// CHECK:interface ImplicitAs {
-// CHECK:********** type checking **********
-// CHECK:** declaring interface ImplicitAs
-// CHECK:********** resolving unformed variables **********
-// CHECK:********** printing declarations **********
-// CHECK:interface ImplicitAs {
-// CHECK:********** starting execution **********
-// CHECK:********** initializing globals **********
-// CHECK:********** calling main function **********
-// CHECK:--- step exp Main() .0. (<Main()>:0) --->
-// CHECK:result: 0
+// CHECK:STDOUT: ********** source program **********
+// CHECK:STDOUT: interface ImplicitAs {
+// CHECK:STDOUT: ********** type checking **********
+// CHECK:STDOUT: ** declaring interface ImplicitAs
+// CHECK:STDOUT: ********** resolving unformed variables **********
+// CHECK:STDOUT: ********** printing declarations **********
+// CHECK:STDOUT: interface ImplicitAs {
+// CHECK:STDOUT: ********** starting execution **********
+// CHECK:STDOUT: ********** initializing globals **********
+// CHECK:STDOUT: ********** calling main function **********
+// CHECK:STDOUT: --- step exp Main() .0. (<Main()>:0) --->
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/var_tuple.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/basic_syntax/zero.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/block/empty.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/block/shadowing.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/choice/generic_choice_multiple_template_arguments.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 22
+// CHECK:STDOUT: result: 22
 
 package ExplorerTest api;
 

explorer/testdata/choice/generic_choice_nested_in_template_class.carbon

@@ -2,11 +2,11 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:H 22
-// CHECK:result: 0
+// CHECK:STDOUT: H 22
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/choice/generic_choice_simple_assignment.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 22
+// CHECK:STDOUT: result: 22
 
 package ExplorerTest api;
 

explorer/testdata/class/assign.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/assign_member.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/bound_method.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/class_function.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/class_function_from_instance.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/class_function_self.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/class_function_value.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/empty_class.carbon

@@ -2,10 +2,10 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
-// CHECK:result: 0
+// CHECK:STDOUT: result: 0
 
 package ExplorerTest api;
 

explorer/testdata/class/fail_abstract_class.carbon

@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 abstract class C {
   fn F() {}
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_abstract_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_abstract_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
 }
 
 fn Main() -> i32 {

explorer/testdata/class/fail_base_class.carbon

@@ -2,15 +2,15 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 base class C {
   fn F() {}
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_base_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_base_class.carbon:[[@LINE+1]]: Class prefixes `base` and `abstract` are not supported yet
 }
 
 fn Main() -> i32 {

explorer/testdata/class/fail_class_extends.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +14,7 @@ class A {
 
 class B extends A {
   fn F() {}
-// CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_class_extends.carbon:[[@LINE+1]]: Class extension with `extends` is not supported yet
+// CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_class_extends.carbon:[[@LINE+1]]: Class extension with `extends` is not supported yet
 }
 
 fn Main() -> i32 {

explorer/testdata/class/fail_class_named_self.carbon

@@ -2,14 +2,14 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
 
 // Error: Can't use keyword `Self` as the name of a class.
-// CHECK:SYNTAX ERROR: {{.*}}/explorer/testdata/class/fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
+// CHECK:STDERR: SYNTAX ERROR: {{.*}}/explorer/testdata/class/fail_class_named_self.carbon:[[@LINE+1]]: syntax error, unexpected SELF, expecting identifier
 class Self {
   var x: i32;
   var y: i32;

explorer/testdata/class/fail_field_access_mismatch.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -15,6 +15,6 @@ class Point {
 
 fn Main() -> i32 {
   var p: Point = {.x = 1, .y = 2};
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_access_mismatch.carbon:[[@LINE+1]]: class Point does not have a field named z
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_access_mismatch.carbon:[[@LINE+1]]: class Point does not have a field named z
   return p.z - 1;
 }

explorer/testdata/class/fail_field_mismatch.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +14,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_mismatch.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32, .z: i32}' is not implicitly convertible to 'class Point'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_mismatch.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32, .z: i32}' is not implicitly convertible to 'class Point'
   var p: Point = {.x = 1, .z = 2};
   return p.x - 1;
 }

explorer/testdata/class/fail_field_missing.carbon

@@ -2,8 +2,8 @@
 // Exceptions. See /LICENSE for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
-// RUN: %{not} %{explorer} %s 2>&1 | %{FileCheck-strict} %s
-// RUN: %{not} %{explorer-trace} %s 2>&1 | %{FileCheck-allow-unmatched} %s
+// RUN: %{not} %{explorer} %s | %{FileCheck-strict} %s
+// RUN: %{not} %{explorer-trace} %s | %{FileCheck-allow-unmatched} %s
 // AUTOUPDATE: %{explorer} %s
 
 package ExplorerTest api;
@@ -14,7 +14,7 @@ class Point {
 }
 
 fn Main() -> i32 {
-  // CHECK:COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_missing.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32}' is not implicitly convertible to 'class Point'
+  // CHECK:STDERR: COMPILATION ERROR: {{.*}}/explorer/testdata/class/fail_field_missing.carbon:[[@LINE+1]]: type error in name binding: '{.x: i32}' is not implicitly convertible to 'class Point'
   var p: Point = {.x = 1};
   return p.x - 1;
 }