[clang] [clang][Sema] Suggest/Hint Standard Library Include File (PR #146227)

[Erich Keane via cfe-commits]

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@@ -804,6 +807,52 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
     assert(SS && SS->isInvalid() &&
            "Invalid scope specifier has already been diagnosed");
   }
+
+  // don't note standard include files for OpenCL and Objective C
+  if ((getLangOpts().CPlusPlus || getLangOpts().C99) && !getLangOpts().OpenCL &&
+      !getLangOpts().ObjC)
+    NoteStandardIncludes(II->getName(), IILoc, SS);
+}
+
+void Sema::NoteStandardIncludes(StringRef SymbolName, SourceLocation IILoc,
+                                StringRef Namespace) {
+  using clang::tooling::stdlib::Lang;
+
+  llvm::StringRef HeaderName = "";
+  tooling::stdlib::Lang LangOption = tooling::stdlib::Lang::C;
+  if (getLangOpts().CPlusPlus)
+    LangOption = clang::tooling::stdlib::Lang::CXX;
+
+  if (auto StdSym =
+          tooling::stdlib::Symbol::named(Namespace, SymbolName, LangOption)) {
+    if (auto Header = StdSym->header()) {
+      HeaderName = Header->name();
+      Diag(IILoc, diag::note_standard_lib_include_suggestion)
+          << HeaderName << (Namespace + SymbolName).str();
+
+      // Noting the C/C++ version as well
+      if (StdSym->version() != tooling::stdlib::Unknown) {
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erichkeane wrote:

Version stuff we should be handling via our diagnostic, not doing it this way.

https://github.com/llvm/llvm-project/pull/146227