Track whether a function type has a trailing return type as type sugar. Use this

to pretty-print such function types better, and to fix a case where we were not
instantiating templates in lexical order. In passing, move the Variadic bit from
Type's bitfields to FunctionProtoType to get the Type bitfields down to 32 bits.
Also ensure that we always substitute the return type of a function when
substituting explicitly-specified arguments, since that can cause us to bail
out with a SFINAE error before we hit a hard error in parameter substitution.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150241 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 29 insertions, 17 deletions

diff --git a/lib/Sema/SemaTemplateDeduction.cpp b/lib/Sema/SemaTemplateDeduction.cpp
index 9d711001b3..1d84ce31b2 100644
--- a/lib/Sema/SemaTemplateDeduction.cpp
+++ b/lib/Sema/SemaTemplateDeduction.cpp
@@ -2291,33 +2291,45 @@ Sema::SubstituteExplicitTemplateArguments(
     }
   }
 
+  const FunctionProtoType *Proto
+    = Function->getType()->getAs<FunctionProtoType>();
+  assert(Proto && "Function template does not have a prototype?");
+
   // Instantiate the types of each of the function parameters given the
-  // explicitly-specified template arguments.
-  if (SubstParmTypes(Function->getLocation(),
+  // explicitly-specified template arguments. If the function has a trailing
+  // return type, substitute it after the arguments to ensure we substitute
+  // in lexical order.
+  if (Proto->hasTrailingReturn() &&
+      SubstParmTypes(Function->getLocation(),
                      Function->param_begin(), Function->getNumParams(),
                      MultiLevelTemplateArgumentList(*ExplicitArgumentList),
                      ParamTypes))
     return TDK_SubstitutionFailure;
 
-  // If the caller wants a full function type back, instantiate the return
-  // type and form that function type.
-  if (FunctionType) {
-    // FIXME: exception-specifications?
-    const FunctionProtoType *Proto
-      = Function->getType()->getAs<FunctionProtoType>();
-    assert(Proto && "Function template does not have a prototype?");
-
-    QualType ResultType
-      = SubstType(Proto->getResultType(),
-                  MultiLevelTemplateArgumentList(*ExplicitArgumentList),
-                  Function->getTypeSpecStartLoc(),
-                  Function->getDeclName());
-    if (ResultType.isNull() || Trap.hasErrorOccurred())
-      return TDK_SubstitutionFailure;
+  // Instantiate the return type.
+  // FIXME: exception-specifications?
+  QualType ResultType
+    = SubstType(Proto->getResultType(),
+                MultiLevelTemplateArgumentList(*ExplicitArgumentList),
+                Function->getTypeSpecStartLoc(),
+                Function->getDeclName());
+  if (ResultType.isNull() || Trap.hasErrorOccurred())
+    return TDK_SubstitutionFailure;
 
+  // Instantiate the types of each of the function parameters given the
+  // explicitly-specified template arguments if we didn't do so earlier.
+  if (!Proto->hasTrailingReturn() &&
+      SubstParmTypes(Function->getLocation(),
+                     Function->param_begin(), Function->getNumParams(),
+                     MultiLevelTemplateArgumentList(*ExplicitArgumentList),
+                     ParamTypes))
+    return TDK_SubstitutionFailure;
+
+  if (FunctionType) {
     *FunctionType = BuildFunctionType(ResultType,
                                       ParamTypes.data(), ParamTypes.size(),
                                       Proto->isVariadic(),
+                                      Proto->hasTrailingReturn(),
                                       Proto->getTypeQuals(),
                                       Proto->getRefQualifier(),
                                       Function->getLocation(),