[clang] [Clang][Diagnostics] Mention 'import std' in typeid diagnostic (PR #173236)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Yuki (AltriaSuki)

<details>
<summary>Changes</summary>

Previously, the diagnostic only suggested including `<typeinfo>`. Since C++20,the standard library may also be made available via `import std;`.

This change updates the diagnostic to mention `import std` as an alternative and adds a test to cover the new wording.

---
Full diff: https://github.com/llvm/llvm-project/pull/173236.diff


2 Files Affected:

- (modified) clang/include/clang/Basic/DiagnosticSemaKinds.td (+1-1) 
- (added) clang/test/SemaCXX/typeid-requires-typeinfo.cpp (+9) 


``````````diff
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 49eee0c2fa617..a8bff4d789b38 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8429,7 +8429,7 @@ def err_bad_dynamic_cast_not_polymorphic : Error<"%0 is not polymorphic">;
 
 // Other C++ expressions
 def err_need_header_before_typeid : Error<
-  "you need to include <typeinfo> before using the 'typeid' operator">;
+  "you need to include <typeinfo> or import std before using the 'typeid' operator">;
 def err_need_header_before_placement_new : Error<
   "no matching %0 function for non-allocating placement new expression; "
   "include <new>">;
diff --git a/clang/test/SemaCXX/typeid-requires-typeinfo.cpp b/clang/test/SemaCXX/typeid-requires-typeinfo.cpp
new file mode 100644
index 0000000000000..ec8773b438c28
--- /dev/null
+++ b/clang/test/SemaCXX/typeid-requires-typeinfo.cpp
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -fsyntax-only -verify -std=c++17 %s
+
+class A{};
+
+auto f() {
+  return typeid(A);
+}
+
+// CHECK: error: you need to include <typeinfo> or import std before using the 'typeid' operator
\ No newline at end of file

``````````

</details>


https://github.com/llvm/llvm-project/pull/173236