[clang][Sema] Don't emit 'declared here' note for builtin functions w…

…ith no decl in source (#93394)

Fixes #93369

---------

Co-authored-by: Timm Baeder <tbaeder@redhat.com>
Co-authored-by: S. B. Tam <cpplearner@outlook.com>

clang/docs/ReleaseNotes.rst

@@ -541,6 +541,9 @@ Improvements to Clang's diagnostics
 - Clang emits a ``-Wparentheses`` warning for expressions with consecutive comparisons like ``x < y < z``.
   Fixes #GH20456.
 
+- Clang no longer emits a "declared here" note for a builtin function that has no declaration in source.
+  Fixes #GH93369.
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/Sema/SemaLookup.cpp

@@ -5897,6 +5897,16 @@ void Sema::diagnoseTypo(const TypoCorrection &Correction,
 
   NamedDecl *ChosenDecl =
       Correction.isKeyword() ? nullptr : Correction.getFoundDecl();
+
+  // For builtin functions which aren't declared anywhere in source,
+  // don't emit the "declared here" note.
+  if (const auto *FD = dyn_cast_if_present<FunctionDecl>(ChosenDecl);
+      FD && FD->getBuiltinID() &&
+      PrevNote.getDiagID() == diag::note_previous_decl &&
+      Correction.getCorrectionRange().getBegin() == FD->getBeginLoc()) {
+    ChosenDecl = nullptr;
+  }
+
   if (PrevNote.getDiagID() && ChosenDecl)
     Diag(ChosenDecl->getLocation(), PrevNote)
       << CorrectedQuotedStr << (ErrorRecovery ? FixItHint() : FixTypo);

clang/test/SemaCXX/invalid-if-constexpr.cpp

@@ -4,8 +4,7 @@ namespace GH61885 {
 void similar() { // expected-note {{'similar' declared here}}
   if constexpr (similer<>) {} // expected-error {{use of undeclared identifier 'similer'; did you mean 'similar'?}}
 }
-void a() { if constexpr (__adl_swap<>) {}} // expected-error{{use of undeclared identifier '__adl_swap'; did you mean '__sync_swap'?}} \
-                                           // expected-note {{'__sync_swap' declared here}}
+void a() { if constexpr (__adl_swap<>) {}} // expected-error{{use of undeclared identifier '__adl_swap'; did you mean '__sync_swap'?}}
 
 int AA() { return true;} // expected-note {{'AA' declared here}}
 

clang/test/SemaCXX/typo-correction-builtin-func.cpp

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+// Test that clang does not emit 'declared here' note for builtin functions that don't have a declaration in source.
+
+void t0() {
+  constexpr float A = __builtin_isinfinity(); // expected-error {{use of undeclared identifier '__builtin_isinfinity'; did you mean '__builtin_isfinite'?}}
+                                              // expected-error@-1 {{too few arguments to function call, expected 1, have 0}}
+}