[SemaOverload] Fixed crash on code completion

Summary:
The relevant failing assertion message is:
../tools/clang/lib/Sema/SemaInit.cpp:8411: PerformCopyInitialization(): Assertion `InitE && "No initialization expression?"' failed.

See the added test case for a repro.

Reviewers: bkramer, sammccall, ioeric, hokein

Reviewed By: sammccall

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D44300

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@327134 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Sema/SemaOverload.cpp

@@ -6245,12 +6245,17 @@ convertArgsForAvailabilityChecks(Sema &S, FunctionDecl *Function, Expr *ThisArg,
   if (!Function->isVariadic() && Args.size() < Function->getNumParams()) {
     for (unsigned i = Args.size(), e = Function->getNumParams(); i != e; ++i) {
       ParmVarDecl *P = Function->getParamDecl(i);
-      ExprResult R = S.PerformCopyInitialization(
-          InitializedEntity::InitializeParameter(S.Context,
-                                                 Function->getParamDecl(i)),
-          SourceLocation(),
-          P->hasUninstantiatedDefaultArg() ? P->getUninstantiatedDefaultArg()
-                                           : P->getDefaultArg());
+      Expr *DefArg = P->hasUninstantiatedDefaultArg()
+                         ? P->getUninstantiatedDefaultArg()
+                         : P->getDefaultArg();
+      // This can only happen in code completion, i.e. when PartialOverloading
+      // is true.
+      if (!DefArg)
+        return false;
+      ExprResult R =
+          S.PerformCopyInitialization(InitializedEntity::InitializeParameter(
+                                          S.Context, Function->getParamDecl(i)),
+                                      SourceLocation(), DefArg);
       if (R.isInvalid())
         return false;
       ConvertedArgs.push_back(R.get());

test/CodeCompletion/enable-if-attr-crash.cpp

@@ -0,0 +1,8 @@
+int foo(bool x) __attribute__((enable_if(x, "")));
+
+int test() {
+  bool fffffff;
+  // RUN: %clang_cc1 -std=c++11 -code-completion-at=%s:7:8 %s | FileCheck %s
+  // CHECK: COMPLETION: fffffff : [#bool#]fffffff
+  foo(ff
+}