Partial revert of r290511.

The rules around typechecking deduced template arguments during partial
ordering are not clear, and while the prior behavior does not seem to be
correct (it doesn't follow the general model of partial ordering where each
template parameter is replaced by a non-dependent but unique value), the new
behavior is also not clearly right and breaks some existing idioms.

The new behavior is retained for dealing with non-type template parameters
with 'auto' types, as without it even the most basic uses of that feature
don't work. We can revisit this once CWG has come to an agreement on how
partial ordering with 'auto' non-type template parameters is supposed to
work.

llvm-svn: 292183

1 files changed, 16 insertions, 12 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 1c19f67cb0f..2920ede3b5e 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -5123,18 +5123,22 @@ ExprResult Sema::CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
   if (CTAK == CTAK_Deduced &&
       !Context.hasSameType(ParamType.getNonLValueExprType(Context),
                            Arg->getType())) {
-    // C++ [temp.deduct.type]p17: (DR1770)
-    //   If P has a form that contains <i>, and if the type of i differs from
-    //   the type of the corresponding template parameter of the template named
-    //   by the enclosing simple-template-id, deduction fails.
-    //
-    // Note that CTAK will be CTAK_DeducedFromArrayBound if the form was [i]
-    // rather than <i>.
-    //
-    // FIXME: We interpret the 'i' here as referring to the expression
-    // denoting the non-type template parameter rather than the parameter
-    // itself, and so strip off references before comparing types. It's
-    // not clear how this is supposed to work for references.
+    // FIXME: If either type is dependent, we skip the check. This isn't
+    // correct, since during deduction we're supposed to have replaced each
+    // template parameter with some unique (non-dependent) placeholder.
+    // FIXME: If the argument type contains 'auto', we carry on and fail the
+    // type check in order to force specific types to be more specialized than
+    // 'auto'. It's not clear how partial ordering with 'auto' is supposed to
+    // work.
+    if ((ParamType->isDependentType() || Arg->isTypeDependent()) &&
+        !Arg->getType()->getContainedAutoType()) {
+      Converted = TemplateArgument(Arg);
+      return Arg;
+    }
+    // FIXME: This attempts to implement C++ [temp.deduct.type]p17. Per DR1770,
+    // we should actually be checking the type of the template argument in P,
+    // not the type of the template argument deduced from A, against the
+    // template parameter type.
     Diag(StartLoc, diag::err_deduced_non_type_template_arg_type_mismatch)
       << Arg->getType()
       << ParamType.getUnqualifiedType();