[Clang] Don't ditch typo-corrected lookup result (#139374)

For a member function call like 'foo.bar<int>()', there are two
typo-correction points after parsing the dot. The first occurs in
ParseOptionalCXXScopeSpecifier, which tries to annotate the template
name following any scope specifiers.

If the template name bar is not found within 'foo', the parser was
previously instructed to drop any function templates found outside of
the scope. This was intended to prevent ambiguity in expressions like
'foo->bar < 7', as explained in commit 50a3cdd. However, it's
unnecessary to discard typo-corrected results that were strictly
resolved within the scope 'foo'.

We won't perform a second typo-correction in ParseUnqualifiedId after
the name being annotated.

Fixes #139226

Author: zyn0217

clang/docs/ReleaseNotes.rst

@@ -517,7 +517,10 @@ Improvements to Clang's diagnostics
 
 - Improved the ``-Wtautological-overlap-compare`` diagnostics to warn about overlapping and non-overlapping ranges involving character literals and floating-point literals. 
   The warning message for non-overlapping cases has also been improved (#GH13473).
-  
+
+- Fixed a duplicate diagnostic when performing typo correction on function template
+  calls with explicit template arguments. (#GH139226)
+
 Improvements to Clang's time-trace
 ----------------------------------
 

clang/lib/Sema/SemaTemplate.cpp

@@ -523,6 +523,9 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
       if (Found.isAmbiguous()) {
         Found.clear();
       } else if (!Found.empty()) {
+        // Do not erase the typo-corrected result to avoid duplicated
+        // diagnostics.
+        AllowFunctionTemplatesInLookup = true;
         Found.setLookupName(Corrected.getCorrection());
         if (LookupCtx) {
           std::string CorrectedStr(Corrected.getAsString(getLangOpts()));

clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1.cpp

@@ -98,3 +98,16 @@ namespace PR11856 {
     }
   }
 }
+
+namespace GH139226 {
+
+struct Foo {
+  template <class T> void LookupWithID(); // expected-note {{declared here}}
+};
+
+void test(Foo &f) {
+  f.LookupWithId<int>();
+  // expected-error@-1 {{did you mean 'LookupWithID'}}
+}
+
+}