Add a test for the case that `impl` function is poisoned (#4950)

This adds missing coverage.
Part of #4622.

toolchain/check/testdata/function/declaration/no_prelude/name_poisoning.carbon

@@ -94,6 +94,7 @@ alias N.F2 = F1;
 fn N.F1();
 
 // Failure: `N.F1` used after declaration failed.
+// TODO: #4622 - Allow defining a poisoned name so it would be found if used after it's declared.
 // CHECK:STDERR: fail_use_declaration_after_poison.carbon:[[@LINE+4]]:14: error: member name `F1` not found in `N` [MemberNameNotFoundInScope]
 // CHECK:STDERR: alias N.F3 = N.F1;
 // CHECK:STDERR:              ^~~~
@@ -414,7 +415,7 @@ fn F1() {
 // CHECK:STDOUT:   %F2: %F1.type.75d = bind_alias F2, %F1.decl.loc4 [concrete = constants.%F1.afe]
 // CHECK:STDOUT:   %F1.decl.loc18: %F1.type.fe6 = fn_decl @F1.2 [concrete = constants.%F1.cc1] {} {}
 // CHECK:STDOUT:   %N.ref: <namespace> = name_ref N, %N [concrete = %N]
-// CHECK:STDOUT:   %F1.ref.loc25: <error> = name_ref F1, <error> [concrete = <error>]
+// CHECK:STDOUT:   %F1.ref.loc26: <error> = name_ref F1, <error> [concrete = <error>]
 // CHECK:STDOUT:   %F3: <error> = bind_alias F3, <error> [concrete = <error>]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:

toolchain/check/testdata/impl/no_prelude/name_poisoning.carbon

@@ -23,6 +23,37 @@ class N.C {
   }
 }
 
+// --- fail_impl_function_poisoned.carbon
+
+library "[[@TEST_NAME]]";
+
+interface I {
+  fn A(x: Self);
+  fn B();
+}
+
+class B {
+  impl as I {
+    // CHECK:STDERR: fail_impl_function_poisoned.carbon:[[@LINE+3]]:13: error: name `B` used before it was declared [NameUseBeforeDecl]
+    // CHECK:STDERR:     fn A(x: B);
+    // CHECK:STDERR:             ^
+    fn A(x: B);
+    // TODO: Avoid ImplMissingFunction for functions that were declared after they were poisoned.
+    // CHECK:STDERR: fail_impl_function_poisoned.carbon:[[@LINE+11]]:8: note: declared here [NameUseBeforeDeclNote]
+    // CHECK:STDERR:     fn B();
+    // CHECK:STDERR:        ^
+    // CHECK:STDERR:
+    // CHECK:STDERR: fail_impl_function_poisoned.carbon:[[@LINE-10]]:3: error: missing implementation of B in impl of interface I [ImplMissingFunction]
+    // CHECK:STDERR:   impl as I {
+    // CHECK:STDERR:   ^~~~~~~~~~~
+    // CHECK:STDERR: fail_impl_function_poisoned.carbon:[[@LINE-17]]:3: note: associated function B declared here [AssociatedFunctionHere]
+    // CHECK:STDERR:   fn B();
+    // CHECK:STDERR:   ^~~~~~~
+    // CHECK:STDERR:
+    fn B();
+  }
+}
+
 // CHECK:STDOUT: --- using_poisoned_name_in_impl.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
@@ -100,3 +131,120 @@ class N.C {
 // CHECK:STDOUT:   %x.patt.loc8_9.2 => constants.%x
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
+// CHECK:STDOUT: --- fail_impl_function_poisoned.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %I.type: type = facet_type <@I> [concrete]
+// CHECK:STDOUT:   %Self: %I.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %Self.as_type: type = facet_access_type %Self [symbolic]
+// CHECK:STDOUT:   %A.type.edf: type = fn_type @A.1 [concrete]
+// CHECK:STDOUT:   %A.ab0: %A.type.edf = struct_value () [concrete]
+// CHECK:STDOUT:   %I.assoc_type: type = assoc_entity_type %I.type [concrete]
+// CHECK:STDOUT:   %assoc0: %I.assoc_type = assoc_entity element0, @I.%A.decl [concrete]
+// CHECK:STDOUT:   %B.type.785: type = fn_type @B.1 [concrete]
+// CHECK:STDOUT:   %B.6d4: %B.type.785 = struct_value () [concrete]
+// CHECK:STDOUT:   %assoc1: %I.assoc_type = assoc_entity element1, @I.%B.decl [concrete]
+// CHECK:STDOUT:   %B.fa3: type = class_type @B.3 [concrete]
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.%A.decl, <error>) [concrete]
+// CHECK:STDOUT:   %A.type.9b9: type = fn_type @A.2 [concrete]
+// CHECK:STDOUT:   %A.71f: %A.type.9b9 = struct_value () [concrete]
+// CHECK:STDOUT:   %B.type.52d: type = fn_type @B.2 [concrete]
+// CHECK:STDOUT:   %B.30a: %B.type.52d = struct_value () [concrete]
+// CHECK:STDOUT:   %I.facet: %I.type = facet_value %B.fa3, %impl_witness [concrete]
+// CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [concrete]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [concrete]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [concrete] {
+// CHECK:STDOUT:     .I = %I.decl
+// CHECK:STDOUT:     .B = %B.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %I.decl: type = interface_decl @I [concrete = constants.%I.type] {} {}
+// CHECK:STDOUT:   %B.decl: type = class_decl @B.3 [concrete = constants.%B.fa3] {} {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @I {
+// CHECK:STDOUT:   %Self: %I.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
+// CHECK:STDOUT:   %A.decl: %A.type.edf = fn_decl @A.1 [concrete = constants.%A.ab0] {
+// CHECK:STDOUT:     %x.patt: @A.1.%Self.as_type.loc5_11.1 (%Self.as_type) = binding_pattern x
+// CHECK:STDOUT:     %x.param_patt: @A.1.%Self.as_type.loc5_11.1 (%Self.as_type) = value_param_pattern %x.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %x.param: @A.1.%Self.as_type.loc5_11.1 (%Self.as_type) = value_param runtime_param0
+// CHECK:STDOUT:     %.loc5_11.1: type = splice_block %.loc5_11.2 [symbolic = %Self.as_type.loc5_11.1 (constants.%Self.as_type)] {
+// CHECK:STDOUT:       %Self.ref: %I.type = name_ref Self, @I.%Self [symbolic = %Self (constants.%Self)]
+// CHECK:STDOUT:       %Self.as_type.loc5_11.2: type = facet_access_type %Self.ref [symbolic = %Self.as_type.loc5_11.1 (constants.%Self.as_type)]
+// CHECK:STDOUT:       %.loc5_11.2: type = converted %Self.ref, %Self.as_type.loc5_11.2 [symbolic = %Self.as_type.loc5_11.1 (constants.%Self.as_type)]
+// CHECK:STDOUT:     }
+// CHECK:STDOUT:     %x: @A.1.%Self.as_type.loc5_11.1 (%Self.as_type) = bind_name x, %x.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %assoc0: %I.assoc_type = assoc_entity element0, %A.decl [concrete = constants.%assoc0]
+// CHECK:STDOUT:   %B.decl: %B.type.785 = fn_decl @B.1 [concrete = constants.%B.6d4] {} {}
+// CHECK:STDOUT:   %assoc1: %I.assoc_type = assoc_entity element1, %B.decl [concrete = constants.%assoc1]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .A = %assoc0
+// CHECK:STDOUT:   .B = %assoc1
+// CHECK:STDOUT:   witness = (%A.decl, %B.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl: %Self.ref as %I.ref {
+// CHECK:STDOUT:   %A.decl: %A.type.9b9 = fn_decl @A.2 [concrete = constants.%A.71f] {
+// CHECK:STDOUT:     %x.patt: %B.fa3 = binding_pattern x
+// CHECK:STDOUT:     %x.param_patt: %B.fa3 = value_param_pattern %x.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %x.param: %B.fa3 = value_param runtime_param0
+// CHECK:STDOUT:     %B.ref: type = name_ref B, file.%B.decl [concrete = constants.%B.fa3]
+// CHECK:STDOUT:     %x: %B.fa3 = bind_name x, %x.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %B.decl: %B.type.52d = fn_decl @B.2 [concrete = constants.%B.30a] {} {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .B = <poisoned>
+// CHECK:STDOUT:   .A = %A.decl
+// CHECK:STDOUT:   witness = @B.3.%impl_witness
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @B.3 {
+// CHECK:STDOUT:   impl_decl @impl [concrete] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%B.fa3 [concrete = constants.%B.fa3]
+// CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [concrete = constants.%I.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.%A.decl, <error>) [concrete = constants.%impl_witness]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [concrete = constants.%complete_type]
+// CHECK:STDOUT:   complete_type_witness = %complete_type
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%B.fa3
+// CHECK:STDOUT:   .I = <poisoned>
+// CHECK:STDOUT:   .B = <poisoned>
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @A.1(@I.%Self: %I.type) {
+// CHECK:STDOUT:   %Self: %I.type = bind_symbolic_name Self, 0 [symbolic = %Self (constants.%Self)]
+// CHECK:STDOUT:   %Self.as_type.loc5_11.1: type = facet_access_type %Self [symbolic = %Self.as_type.loc5_11.1 (constants.%Self.as_type)]
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn(%x.param_patt: @A.1.%Self.as_type.loc5_11.1 (%Self.as_type));
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @B.1(@I.%Self: %I.type) {
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @A.2(%x.param_patt: %B.fa3);
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @B.2();
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @A.1(constants.%Self) {
+// CHECK:STDOUT:   %Self => constants.%Self
+// CHECK:STDOUT:   %Self.as_type.loc5_11.1 => constants.%Self.as_type
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @B.1(constants.%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @A.1(constants.%I.facet) {
+// CHECK:STDOUT:   %Self => constants.%I.facet
+// CHECK:STDOUT:   %Self.as_type.loc5_11.1 => constants.%B.fa3
+// CHECK:STDOUT: }
+// CHECK:STDOUT: