[PATCH] D36253: [Sema] Add a comment on an identified bug on default arguments.

[Tim Shen via Phabricator via cfe-commits]

timshen created this revision.
Herald added a subscriber: sanjoy.

The mis-compile is triggered by internal code, but I haven't reduced it to a small piece of code. Add a FIXME here, since a decent fix doesn't seem to be trivial.

The decent fix can be changing Decl::Init to PointerUnion<Stmt *, EvaluatedStmt *, ParamVarDecl *>, and make setUninstantiatedDefaultArg take a ParamVarDecl *, which contains the Expr * as the default argument. This way, getTemplateInstantiationArgs can take that ParamVarDecl and do the right thing.


https://reviews.llvm.org/D36253

Files:
  clang/lib/Sema/SemaExpr.cpp


Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -4477,6 +4477,22 @@
         *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
 
     // Instantiate the expression.
+    //
+    // FIXME: Pass in a correct Pattern argument, otherwise
+    // getTemplateInstantiationArgs uses the lexical context of FD, e.g.
+    //
+    // template<typename T>
+    // struct A {
+    //   static int FooImpl();
+    //
+    //   template<typename Tp>
+    //   // bug: default argument A<T>::FooImpl() is evaluated with 2-level
+    //   // template argument list [[T], [Tp]], should be [[Tp]].
+    //   friend A<Tp> Foo(int a);
+    // };
+    //
+    // template<typename T>
+    // A<T> Foo(int a = A<T>::FooImpl());
     MultiLevelTemplateArgumentList MutiLevelArgList
       = getTemplateInstantiationArgs(FD, nullptr, /*RelativeToPrimary=*/true);
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D36253.109461.patch
Type: text/x-patch
Size: 979 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20170803/40eba2d0/attachment-0001.bin>