[PATCH] D138210: [clang] Require parameter pack to be last argument in concepts.

[Luke Nihlen via Phabricator via cfe-commits]

luken-google created this revision.
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Fixes GH48182.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D138210

Files:
  clang/lib/Sema/SemaTemplate.cpp
  clang/test/SemaTemplate/concepts.cpp


Index: clang/test/SemaTemplate/concepts.cpp
===================================================================
--- clang/test/SemaTemplate/concepts.cpp
+++ clang/test/SemaTemplate/concepts.cpp
@@ -766,3 +766,24 @@
   __iterator_traits_member_pointer_or_arrow_or_void<counted_iterator<int>> f;
 }
 }// namespace InheritedFromPartialSpec
+
+namespace GH48182 {
+template<typename, typename..., typename = int> // expected-error{{template parameter pack must be the last template parameter}}
+concept invalid = true;
+
+template<typename> requires invalid<int> // expected-error{{use of undeclared identifier 'invalid'}}
+no errors are printed
+;
+
+static_assert(invalid<int> also here ; // expected-error{{use of undeclared identifier 'invalid'}}
+
+int foo() {
+    bool b;
+    b = invalid<int> not just in declarations; // expected-error{{expected ';' after expression}}
+                                               // expected-error at -1{{use of undeclared identifier 'invalid'}}
+                                               // expected-error at -2{{expected ';' after expression}}
+                                               // expected-error at -3{{use of undeclared identifier 'just'}}
+                                               // expected-error at -4{{unknown type name 'in'}}
+    return b;
+}
+} // namespace GH48182
\ No newline at end of file
Index: clang/lib/Sema/SemaTemplate.cpp
===================================================================
--- clang/lib/Sema/SemaTemplate.cpp
+++ clang/lib/Sema/SemaTemplate.cpp
@@ -8923,17 +8923,31 @@
     return nullptr;
   }
 
-  if (TemplateParameterLists.front()->size() == 0) {
+  TemplateParameterList *Params = TemplateParameterLists.front();
+
+  if (Params->size() == 0) {
     Diag(NameLoc, diag::err_concept_no_parameters);
     return nullptr;
   }
 
+  for (TemplateParameterList::const_iterator ParamIt = Params->begin(),
+                                             ParamEnd = Params->end();
+       ParamIt != ParamEnd; ++ParamIt) {
+    Decl const *Param = *ParamIt;
+    if (Param->isParameterPack()) {
+      if (++ParamIt == ParamEnd)
+        break;
+      Diag(Param->getLocation(),
+           diag::err_template_param_pack_must_be_last_template_parameter);
+      return nullptr;
+    }
+  }
+
   if (DiagnoseUnexpandedParameterPack(ConstraintExpr))
     return nullptr;
 
-  ConceptDecl *NewDecl = ConceptDecl::Create(Context, DC, NameLoc, Name,
-                                             TemplateParameterLists.front(),
-                                             ConstraintExpr);
+  ConceptDecl *NewDecl =
+      ConceptDecl::Create(Context, DC, NameLoc, Name, Params, ConstraintExpr);
 
   if (NewDecl->hasAssociatedConstraints()) {
     // C++2a [temp.concept]p4:


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