[PATCH] D127638: [clang][sema] Provide better diagnostic for missing template parameters

[Timm Bäder via Phabricator via cfe-commits]

tbaeder created this revision.
tbaeder added reviewers: dblaikie, aaron.ballman.
Herald added a project: All.
tbaeder requested review of this revision.
Herald added a project: clang.
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This fixes https://github.com/llvm/llvm-project/issues/55962

i.e. instead of the output being

  ./test.cpp:5:9: error: 'x' is not a class, namespace, or enumeration
  int y = x::a;
          ^
  ./test.cpp:2:8: note: 'x' declared here
  struct x;
         ^
  1 error generated.

it is now:

  ./test.cpp:5:9: error: use of class template 'x' requires template arguments
  int y = x::a;
          ^
  ./test.cpp:2:8: note: template is declared here
  struct x;
         ^
  1 error generated.

Note that the call to `isTemplateName()` is basically copied from `DiagnoseUnknownTypeName()` in `SemaDecl.cpp`. However, just calling that from `SemaCXXScopeSpec.cpp` as well makes the `SemaObjCXX/property-dot-error.mm` test fail, because it now outputs

  clang/test/SemaObjCXX/propert-dot-error.mm Line 67: unknown type name 'D'; did you mean 'D'?
  clang/test/SemaObjCXX/propert-dot-error.mm Line 68: unknown type name 'D'; did you mean 'D'?

and I don't know enough about objc to fix this, but if anyone has some pointers I'd be happy to avoid the code duplication.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D127638

Files:
  clang/lib/Sema/SemaCXXScopeSpec.cpp
  clang/test/SemaCXX/nested-name-spec.cpp


Index: clang/test/SemaCXX/nested-name-spec.cpp
===================================================================
--- clang/test/SemaCXX/nested-name-spec.cpp
+++ clang/test/SemaCXX/nested-name-spec.cpp
@@ -473,3 +473,10 @@
     x: goto x;
   }
 }
+
+template <typename T>
+struct x; // expected-note {{template is declared here}}
+
+template <typename T>
+int issue55962 = x::a; // expected-error {{use of class template 'x' requires template arguments}} \
+                       // expected-warning {{variable templates are a C++14 extension}}
Index: clang/lib/Sema/SemaCXXScopeSpec.cpp
===================================================================
--- clang/lib/Sema/SemaCXXScopeSpec.cpp
+++ clang/lib/Sema/SemaCXXScopeSpec.cpp
@@ -828,15 +828,30 @@
   }
 
   if (!Found.empty()) {
-    if (TypeDecl *TD = Found.getAsSingle<TypeDecl>())
+    if (TypeDecl *TD = Found.getAsSingle<TypeDecl>()) {
       Diag(IdInfo.IdentifierLoc, diag::err_expected_class_or_namespace)
           << Context.getTypeDeclType(TD) << getLangOpts().CPlusPlus;
-    else {
-      Diag(IdInfo.IdentifierLoc, diag::err_expected_class_or_namespace)
-          << IdInfo.Identifier << getLangOpts().CPlusPlus;
-      if (NamedDecl *ND = Found.getAsSingle<NamedDecl>())
-        Diag(ND->getLocation(), diag::note_entity_declared_at)
-            << IdInfo.Identifier;
+    } else {
+      // Try to diagnose x::y where x is a class template and the
+      // template arguments are missing.
+      UnqualifiedId Name;
+      Name.setIdentifier(IdInfo.Identifier, IdInfo.IdentifierLoc);
+      CXXScopeSpec EmptySS;
+      TemplateTy TemplateResult;
+      bool MemberOfUnknownSpecialization;
+      if (isTemplateName(S, SS, /*hasTemplateKeyword=*/false, Name, nullptr,
+                         true, TemplateResult,
+                         MemberOfUnknownSpecialization) == TNK_Type_template) {
+        diagnoseMissingTemplateArguments(TemplateResult.get(),
+                                         IdInfo.IdentifierLoc);
+      } else {
+        Diag(IdInfo.IdentifierLoc, diag::err_expected_class_or_namespace)
+            << IdInfo.Identifier << getLangOpts().CPlusPlus;
+        if (NamedDecl *ND = Found.getAsSingle<NamedDecl>()) {
+          Diag(ND->getLocation(), diag::note_entity_declared_at)
+              << IdInfo.Identifier;
+        }
+      }
     }
   } else if (SS.isSet())
     Diag(IdInfo.IdentifierLoc, diag::err_no_member) << IdInfo.Identifier


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