[Clang][Parser] Build up QualifiedTemplateName for typo correction (#108148)

Since #93433, we have switched to `QualifiedTemplateName`s in more
situations to preserve sugars in diagnostics. However, there is one
missed case in typo correction that might not meet the expectation in
`CheckDeductionGuideDeclarator()`.

Fixes #107887

Author: zyn0217

clang/docs/ReleaseNotes.rst

@@ -381,6 +381,7 @@ Bug Fixes to C++ Support
 - Fixed a bug where defaulted comparison operators would remove ``const`` from base classes. (#GH102588)
 - Fix a crash when using ``source_location`` in the trailing return type of a lambda expression. (#GH67134)
 - A follow-up fix was added for (#GH61460), as the previous fix was not entirely correct. (#GH86361)
+- Fixed a crash in the typo correction of an invalid CTAD guide. (#GH107887)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaTemplate.cpp

@@ -3567,7 +3567,9 @@ bool Sema::resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
   if (Corrected && Corrected.getFoundDecl()) {
     diagnoseTypo(Corrected, PDiag(diag::err_no_template_suggest)
                                 << ATN->getDeclName());
-    Name = TemplateName(Corrected.getCorrectionDeclAs<TemplateDecl>());
+    Name = Context.getQualifiedTemplateName(
+        /*NNS=*/nullptr, /*TemplateKeyword=*/false,
+        TemplateName(Corrected.getCorrectionDeclAs<TemplateDecl>()));
     return false;
   }
 

clang/test/Parser/cxx1z-class-template-argument-deduction.cpp

@@ -255,3 +255,15 @@ void f() {
   GH57495::vector.d; // expected-error {{cannot use dot operator on a type}}
 }
 }
+
+namespace GH107887 {
+
+namespace a {
+template <class> struct pair; // expected-note 3{{declared here}}
+}
+template <class T2> pair() -> pair<T2>;   // expected-error 2{{no template named 'pair'}} \
+                                          // expected-error {{deduction guide must be declared in the same scope}} \
+                                          // expected-error {{cannot be deduced}} \
+                                          // expected-note {{non-deducible template parameter 'T2'}}
+
+}