Template Diagnostic Improvements

[bradenhelmer]

It turns out SemaTemplate handles this type of diagnostic already, however when template gets encountered, it never gets parsed as a possible statement or declaration, only as an expression.

Would like some feedback as I am unsure if this is the right fix. Thanks

Fixes #17959.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Braden Helmer (bradenhelmer)

Changes

This is for #17959.

It turns out SemaTemplate handles this type of diagnostic already, however when template gets encountered, it never gets parsed as a possible statement or declaration, only as an expression.

Would like some feedback as I am unsure if this is the right fix. Thanks

---

Full diff: https://github.com/llvm/llvm-project/pull/99933.diff

2 Files Affected:

• (modified) clang/lib/Parse/ParseStmt.cpp (+9)
• (modified) clang/test/Parser/cxx-template-decl.cpp (+4)

diff --git a/clang/lib/Parse/ParseStmt.cpp b/clang/lib/Parse/ParseStmt.cpp
index 22d38adc28ebe..bdb3fc051d0b3 100644
--- a/clang/lib/Parse/ParseStmt.cpp
+++ b/clang/lib/Parse/ParseStmt.cpp
@@ -299,6 +299,15 @@ StmtResult Parser::ParseStatementOrDeclarationAfterAttributes(
     goto Retry;
   }
 
+  case tok::kw_template: {
+    SourceLocation DeclEnd;
+    ParsedAttributes Attrs(AttrFactory);
+    ParseTemplateDeclarationOrSpecialization(DeclaratorContext::Block, DeclEnd,
+                                             Attrs,
+                                             getAccessSpecifierIfPresent());
+    return StmtError();
+  }
+
   case tok::kw_case:                // C99 6.8.1: labeled-statement
     return ParseCaseStatement(StmtCtx);
   case tok::kw_default:             // C99 6.8.1: labeled-statement
diff --git a/clang/test/Parser/cxx-template-decl.cpp b/clang/test/Parser/cxx-template-decl.cpp
index 734438069b9ae..5a2d1cec9ad31 100644
--- a/clang/test/Parser/cxx-template-decl.cpp
+++ b/clang/test/Parser/cxx-template-decl.cpp
@@ -297,3 +297,7 @@ namespace PR46231 {
   template<> int; // expected-error {{declaration does not declare anything}}
   template<int> int; // expected-error {{declaration does not declare anything}}
 }
+
+namespace NoTemplateInBlockScope {
+  void foo() { template <typename> int i; } // expected-error {{templates can only be declared in namespace or class scope}}
+}

[mizvekov]

Hi.

The change looks good.

There are some other examples of bad diagnostics in that issue, and it would be ideal if they are preserved in case this PR closes that issue.

Please also add an entry to clang/docs/ReleaseNotes.rst.

[bradenhelmer]

This is handling the other non-local case now, and the release notes have been updated. The local class case was already being handled.

[mizvekov]

LGTM, Thanks!

Please give it a couple of days before merging, in case anyone else wants to chime in.

[mizvekov]

These updated test changes still LGTM.

[cor3ntin]

LGTM.

[bradenhelmer]

I don't have write access, if someone could merge that would be great!