[PATCH] D22587: [ASTContext] Fix part of DR224 for nontype template arguments

[Matthias Gehre via cfe-commits]

mgehre created this revision.
mgehre added reviewers: klimek, aaron.ballman, rsmith.
mgehre added a subscriber: cfe-commits.

Look through expressions to determine if a nontype template argument has been given the value of the template parameter.

https://reviews.llvm.org/D22587

Files:
  lib/AST/ASTContext.cpp
  test/CXX/drs/dr2xx.cpp

Index: test/CXX/drs/dr2xx.cpp
===================================================================
--- test/CXX/drs/dr2xx.cpp
+++ test/CXX/drs/dr2xx.cpp
@@ -275,9 +275,9 @@
       static const int my_I = I;
       static const int my_I2 = I+0;
       static const int my_I3 = my_I;
-      B<my_T1, T2, my_I>::type b3; // FIXME: expected-error {{missing 'typename'}}
+      B<my_T1, T2, my_I>::type b3;
       B<my_T1, T2, my_I2>::type b4; // expected-error {{missing 'typename'}}
-      B<my_T1, T2, my_I3>::type b5; // FIXME: expected-error {{missing 'typename'}}
+      B<my_T1, T2, my_I3>::type b5;
     };
   }
 
Index: lib/AST/ASTContext.cpp
===================================================================
--- lib/AST/ASTContext.cpp
+++ lib/AST/ASTContext.cpp
@@ -4448,8 +4448,26 @@
     case TemplateArgument::Null:
       return Arg;
 
-    case TemplateArgument::Expression:
+    case TemplateArgument::Expression: {
+      // Look through variable declarations that have been initialized to a non-type template
+      // parameter, see 14.6.2.1 [temp.dep.type]:
+      // [...], the argument must have been given the value of
+      // the template parameter and not an expression involving the template parameter.
+      auto *E = Arg.getAsExpr()->IgnoreImpCasts();
+      while(auto *DeclRef = dyn_cast_or_null<DeclRefExpr>(E)) {
+        auto *D = DeclRef->getDecl();
+        if (isa<NonTypeTemplateParmDecl>(D))
+          return TemplateArgument(DeclRef);
+
+        auto *VD = dyn_cast<VarDecl>(D);
+        if (!VD)
+          break;
+        E = VD->getInit();
+        if (E)
+          E = E->IgnoreImpCasts();
+      }
       return Arg;
+    }
 
     case TemplateArgument::Declaration: {
       ValueDecl *D = cast<ValueDecl>(Arg.getAsDecl()->getCanonicalDecl());


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