[modules] Improve diagnostic for a template-id that's invalid because a default

argument is not visible.

llvm-svn: 239934

1 files changed, 35 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 9a154111226..f4740a5cd85 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -3644,6 +3644,35 @@ static Optional<unsigned> getExpandedPackSize(NamedDecl *Param) {
   return None;
 }
 
+/// Diagnose a missing template argument.
+template<typename TemplateParmDecl>
+static bool diagnoseMissingArgument(Sema &S, SourceLocation Loc,
+                                    TemplateDecl *TD,
+                                    const TemplateParmDecl *D,
+                                    TemplateArgumentListInfo &Args) {
+  // Dig out the most recent declaration of the template parameter; there may be
+  // declarations of the template that are more recent than TD.
+  D = cast<TemplateParmDecl>(cast<TemplateDecl>(TD->getMostRecentDecl())
+                                 ->getTemplateParameters()
+                                 ->getParam(D->getIndex()));
+
+  // If there's a default argument that's not visible, diagnose that we're
+  // missing a module import.
+  llvm::SmallVector<Module*, 8> Modules;
+  if (D->hasDefaultArgument() && !S.hasVisibleDefaultArgument(D, &Modules)) {
+    S.diagnoseMissingImport(Loc, cast<NamedDecl>(TD),
+                            D->getDefaultArgumentLoc(), Modules,
+                            Sema::MissingImportKind::DefaultArgument,
+                            /*Recover*/ true);
+    return true;
+  }
+
+  // FIXME: If there's a more recent default argument that *is* visible,
+  // diagnose that it was declared too late.
+
+  return diagnoseArityMismatch(S, TD, Loc, Args);
+}
+
 /// \brief Check that the given template argument list is well-formed
 /// for specializing the given template.
 bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
@@ -3800,7 +3829,8 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
     // the default argument.
     if (TemplateTypeParmDecl *TTP = dyn_cast<TemplateTypeParmDecl>(*Param)) {
       if (!hasVisibleDefaultArgument(TTP))
-        return diagnoseArityMismatch(*this, Template, TemplateLoc, NewArgs);
+        return diagnoseMissingArgument(*this, TemplateLoc, Template, TTP,
+                                       NewArgs);
 
       TypeSourceInfo *ArgType = SubstDefaultTemplateArgument(*this,
                                                              Template,
@@ -3816,7 +3846,8 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
     } else if (NonTypeTemplateParmDecl *NTTP
                  = dyn_cast<NonTypeTemplateParmDecl>(*Param)) {
       if (!hasVisibleDefaultArgument(NTTP))
-        return diagnoseArityMismatch(*this, Template, TemplateLoc, NewArgs);
+        return diagnoseMissingArgument(*this, TemplateLoc, Template, NTTP,
+                                       NewArgs);
 
       ExprResult E = SubstDefaultTemplateArgument(*this, Template,
                                                               TemplateLoc,
@@ -3833,7 +3864,8 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
         = cast<TemplateTemplateParmDecl>(*Param);
 
       if (!hasVisibleDefaultArgument(TempParm))
-        return diagnoseArityMismatch(*this, Template, TemplateLoc, NewArgs);
+        return diagnoseMissingArgument(*this, TemplateLoc, Template, TempParm,
+                                       NewArgs);
 
       NestedNameSpecifierLoc QualifierLoc;
       TemplateName Name = SubstDefaultTemplateArgument(*this, Template,