Share ReadFile in tests (#4967)

Small cleanup for code sharing. Note, `*ReadFile` will trigger a
CHECK-failure on error; the relevant implementations would previously
have failed silently (empty string).

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>

testing/base/BUILD

@@ -91,6 +91,14 @@ cc_binary(
     ],
 )
 
+cc_library(
+    name = "file_helpers",
+    testonly = 1,
+    srcs = ["file_helpers.cpp"],
+    hdrs = ["file_helpers.h"],
+    deps = ["//common:error"],
+)
+
 cc_library(
     name = "global_exe_path",
     testonly = 1,

testing/base/file_helpers.cpp

@@ -0,0 +1,25 @@
+// 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
+
+#include "testing/base/file_helpers.h"
+
+#include <fstream>
+#include <sstream>
+
+namespace Carbon::Testing {
+
+auto ReadFile(std::filesystem::path path) -> ErrorOr<std::string> {
+  std::ifstream file_stream(path);
+  if (file_stream.fail()) {
+    return Error(llvm::formatv("Error opening file: {0}", path));
+  }
+  std::stringstream buffer;
+  buffer << file_stream.rdbuf();
+  if (file_stream.fail()) {
+    return Error(llvm::formatv("Error reading file: {0}", path));
+  }
+  return buffer.str();
+}
+
+}  // namespace Carbon::Testing

testing/base/file_helpers.h

@@ -0,0 +1,20 @@
+// 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
+
+#ifndef CARBON_TESTING_BASE_FILE_HELPERS_H_
+#define CARBON_TESTING_BASE_FILE_HELPERS_H_
+
+#include <filesystem>
+#include <string>
+
+#include "common/error.h"
+
+namespace Carbon::Testing {
+
+// Reads a file to string.
+auto ReadFile(std::filesystem::path path) -> ErrorOr<std::string>;
+
+}  // namespace Carbon::Testing
+
+#endif  // CARBON_TESTING_BASE_FILE_HELPERS_H_

testing/file_test/BUILD

@@ -39,6 +39,7 @@ cc_library(
         "//common:init_llvm",
         "//common:ostream",
         "//common:raw_string_ostream",
+        "//testing/base:file_helpers",
         "@abseil-cpp//absl/flags:flag",
         "@abseil-cpp//absl/flags:parse",
         "@googletest//:gtest",

testing/file_test/file_test_base.cpp

@@ -7,7 +7,6 @@
 #include <gmock/gmock.h>
 
 #include <filesystem>
-#include <fstream>
 #include <optional>
 #include <string>
 #include <utility>
@@ -28,6 +27,7 @@
 #include "llvm/Support/PrettyStackTrace.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/ThreadPool.h"
+#include "testing/base/file_helpers.h"
 #include "testing/file_test/autoupdate.h"
 
 ABSL_FLAG(std::vector<std::string>, file_tests, {},
@@ -60,21 +60,6 @@ using ::testing::StrEq;
 
 static constexpr llvm::StringLiteral StdinFilename = "STDIN";
 
-// Reads a file to string.
-static auto ReadFile(std::string_view path) -> ErrorOr<std::string> {
-  std::ifstream proto_file{std::string(path)};
-  if (proto_file.fail()) {
-    return Error(llvm::formatv("Error opening file: {0}", path));
-  }
-  std::stringstream buffer;
-  buffer << proto_file.rdbuf();
-  if (proto_file.fail()) {
-    return Error(llvm::formatv("Error reading file: {0}", path));
-  }
-  proto_file.close();
-  return buffer.str();
-}
-
 // Splits outputs to string_view because gtest handles string_view by default.
 static auto SplitOutput(llvm::StringRef output)
     -> llvm::SmallVector<std::string_view> {
@@ -288,7 +273,7 @@ auto FileTestBase::GetLineNumberReplacements(
 auto FileTestBase::ProcessTestFileAndRun(TestContext& context)
     -> ErrorOr<Success> {
   // Store the file so that test_files can use references to content.
-  CARBON_ASSIGN_OR_RETURN(context.input_content, ReadFile(test_name_));
+  CARBON_ASSIGN_OR_RETURN(context.input_content, ReadFile(test_name_.str()));
 
   // Load expected output.
   CARBON_RETURN_IF_ERROR(ProcessTestFile(context));

toolchain/driver/BUILD

@@ -153,6 +153,7 @@ cc_test(
         ":driver",
         "//common:all_llvm_targets",
         "//common:raw_string_ostream",
+        "//testing/base:file_helpers",
         "//testing/base:global_exe_path",
         "//testing/base:gtest_main",
         "//toolchain/diagnostics:diagnostic_emitter",

toolchain/driver/driver_test.cpp

@@ -15,6 +15,7 @@
 #include "llvm/ADT/ScopeExit.h"
 #include "llvm/Object/Binary.h"
 #include "llvm/Support/FormatVariadic.h"
+#include "testing/base/file_helpers.h"
 #include "testing/base/global_exe_path.h"
 #include "toolchain/testing/yaml_test_helpers.h"
 
@@ -28,16 +29,6 @@ using ::testing::StrEq;
 
 namespace Yaml = ::Carbon::Testing::Yaml;
 
-// Reads a file to string.
-// TODO: Extract this to a helper and share it with other tests.
-static auto ReadFile(std::filesystem::path path) -> std::string {
-  std::ifstream proto_file(path);
-  std::stringstream buffer;
-  buffer << proto_file.rdbuf();
-  proto_file.close();
-  return buffer.str();
-}
-
 class DriverTest : public testing::Test {
  public:
   DriverTest()
@@ -222,7 +213,7 @@ TEST_F(DriverTest, FileOutput) {
                   .success);
   EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
   // TODO: This may need to be tailored to other assembly formats.
-  EXPECT_THAT(ReadFile("test.s"), ContainsRegex("Main:"));
+  EXPECT_THAT(*Testing::ReadFile("test.s"), ContainsRegex("Main:"));
 }
 
 }  // namespace

utils/tree_sitter/BUILD

@@ -62,6 +62,7 @@ cc_binary(
     tags = ["manual"],
     deps = [
         ":parser",
+        "//testing/base:file_helpers",
     ],
 )
 
@@ -74,6 +75,7 @@ cc_test(
     tags = ["manual"],
     deps = [
         ":parser",
+        "//testing/base:file_helpers",
     ],
 )
 
@@ -99,6 +101,7 @@ cc_test(
     tags = ["manual"],
     deps = [
         ":parser",
+        "//testing/base:file_helpers",
     ],
 )
 
@@ -114,5 +117,6 @@ cc_test(
     tags = ["manual"],
     deps = [
         ":parser",
+        "//testing/base:file_helpers",
     ],
 )

utils/tree_sitter/test_runner.cpp

@@ -5,28 +5,17 @@
 #include <tree_sitter/api.h>
 
 #include <cstdlib>
-#include <filesystem>
-#include <fstream>
 #include <iostream>
-#include <sstream>
 #include <string>
 #include <vector>
 
+#include "testing/base/file_helpers.h"
 #include "utils/tree_sitter/src/tree_sitter/parser.h"
 
 extern "C" {
 auto tree_sitter_carbon() -> TSLanguage*;
 }
 
-// Reads a file to string.
-static auto ReadFile(std::filesystem::path path) -> std::string {
-  std::ifstream file(path);
-  std::stringstream buffer;
-  buffer << file.rdbuf();
-  file.close();
-  return buffer.str();
-}
-
 // TODO: use file_test.cpp
 auto main(int argc, char** argv) -> int {
   if (argc < 2) {
@@ -42,7 +31,7 @@ auto main(int argc, char** argv) -> int {
   std::vector<std::string> incorrect;
   for (int i = 1; i < argc; i++) {
     std::string file_path = argv[i];
-    std::string source = ReadFile(file_path);
+    std::string source = std::move(*Carbon::Testing::ReadFile(file_path));
 
     auto* tree =
         ts_parser_parse_string(parser, nullptr, source.data(), source.size());