r294773 - [c++1z] Disallow deduction guides with deduced types that don't syntactically match the template being deduced.

[Richard Smith via cfe-commits]

Author: rsmith
Date: Fri Feb 10 13:49:50 2017
New Revision: 294773

URL: http://llvm.org/viewvc/llvm-project?rev=294773&view=rev
Log:
[c++1z] Disallow deduction guides with deduced types that don't syntactically match the template being deduced.

Modified:
    cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
    cfe/trunk/lib/Sema/SemaDeclCXX.cpp
    cfe/trunk/test/CXX/temp/temp.deduct.guide/p3.cpp

Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=294773&r1=294772&r2=294773&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Fri Feb 10 13:49:50 2017
@@ -1981,6 +1981,9 @@ def err_deduced_class_template_explicit
   "%select{constructor|deduction guide}1 for copy-list-initialization">;
 def err_deduction_guide_no_trailing_return_type : Error<
   "deduction guide declaration without trailing return type">;
+def err_deduction_guide_bad_trailing_return_type : Error<
+  "deduced type %1 of deduction guide is not %select{|written as }2"
+  "a specialization of template %0">;
 def err_deduction_guide_with_complex_decl : Error<
   "cannot specify any part of a return type in the "
   "declaration of a deduction guide">;

Modified: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDeclCXX.cpp?rev=294773&r1=294772&r2=294773&view=diff
==============================================================================
--- cfe/trunk/lib/Sema/SemaDeclCXX.cpp (original)
+++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp Fri Feb 10 13:49:50 2017
@@ -8192,12 +8192,46 @@ void Sema::CheckDeductionGuideDeclarator
            diag::err_deduction_guide_no_trailing_return_type);
       break;
     }
+
+    // Check that the return type is written as a specialization of
+    // the template specified as the deduction-guide's name.
+    ParsedType TrailingReturnType = Chunk.Fun.getTrailingReturnType();
+    TemplateName GuidedTemplate = D.getName().TemplateName.get().get();
+    TypeSourceInfo *TSI = nullptr;
+    QualType RetTy = GetTypeFromParser(TrailingReturnType, &TSI);
+    assert(TSI && "deduction guide has valid type but invalid return type?");
+    bool AcceptableReturnType = false;
+    bool MightInstantiateToSpecialization = false;
+    if (auto RetTST =
+            TSI->getTypeLoc().getAs<TemplateSpecializationTypeLoc>()) {
+      TemplateName SpecifiedName = RetTST.getTypePtr()->getTemplateName();
+      bool TemplateMatches =
+          Context.hasSameTemplateName(SpecifiedName, GuidedTemplate);
+      if (SpecifiedName.getKind() == TemplateName::Template && TemplateMatches)
+        AcceptableReturnType = true;
+      else {
+        // This could still instantiate to the right type, unless we know it
+        // names the wrong class template.
+        auto *TD = SpecifiedName.getAsTemplateDecl();
+        MightInstantiateToSpecialization = !(TD && isa<ClassTemplateDecl>(TD) &&
+                                             !TemplateMatches);
+      }
+    } else if (!RetTy.hasQualifiers() && RetTy->isDependentType()) {
+      MightInstantiateToSpecialization = true;
+    }
+
+    if (!AcceptableReturnType) {
+      Diag(TSI->getTypeLoc().getLocStart(),
+           diag::err_deduction_guide_bad_trailing_return_type)
+        << GuidedTemplate << TSI->getType() << MightInstantiateToSpecialization
+        << TSI->getTypeLoc().getSourceRange();
+    }
+
+    // Keep going to check that we don't have any inner declarator pieces (we
+    // could still have a function returning a pointer to a function).
     FoundFunction = true;
   }
 
-  // FIXME: Check that the return type can instantiate to a specialization of
-  // the template specified as the deduction-guide's name.
-
   if (D.isFunctionDefinition())
     Diag(D.getIdentifierLoc(), diag::err_deduction_guide_defines_function);
 }

Modified: cfe/trunk/test/CXX/temp/temp.deduct.guide/p3.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CXX/temp/temp.deduct.guide/p3.cpp?rev=294773&r1=294772&r2=294773&view=diff
==============================================================================
--- cfe/trunk/test/CXX/temp/temp.deduct.guide/p3.cpp (original)
+++ cfe/trunk/test/CXX/temp/temp.deduct.guide/p3.cpp Fri Feb 10 13:49:50 2017
@@ -32,11 +32,9 @@ template<template<typename> typename TT>
   TT(int) -> TT<int>; // expected-error 2{{cannot specify deduction guide for template template parameter 'TT'}} expected-error {{requires an identifier}}
 };
 
-// FIXME: Even if the DR is applied as we hope, we should still warn if the
-// trailing-return-type can obviously never produce a specialization of the
-// named template.
-A(int) -> int;
-template<typename T> A(T) -> T*;
+A(int) -> int; // expected-error {{deduced type 'int' of deduction guide is not a specialization of template 'A'}}
+template<typename T> A(T) -> B<T>; // expected-error {{deduced type 'B<T>' (aka 'A<type-parameter-0-0>') of deduction guide is not written as a specialization of template 'A'}}
+template<typename T> A(T*) -> const A<T>; // expected-error {{deduced type 'const A<T>' of deduction guide is not a specialization of template 'A'}}
 
 // A deduction-guide shall be declared in the same scope as the corresponding
 // class template.