[Sema] Suppress additional warnings for C's zero initializer

Summary:
D28148 relaxed some checks for assigning { 0 } to a structure for all C
standards, but it failed to handle structures with non-integer
subobjects. Relax -Wmissing-braces checks for such structures, and add
some additional tests.

This fixes PR39931.

Patch By: al3xtjames

Reviewed By: Lekensteyn

Differential Revision: https://reviews.llvm.org/D61838

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@366163 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/Expr.cpp

@@ -2303,11 +2303,11 @@ bool InitListExpr::isTransparent() const {
 bool InitListExpr::isIdiomaticZeroInitializer(const LangOptions &LangOpts) const {
   assert(isSyntacticForm() && "only test syntactic form as zero initializer");
 
-  if (LangOpts.CPlusPlus || getNumInits() != 1) {
+  if (LangOpts.CPlusPlus || getNumInits() != 1 || !getInit(0)) {
     return false;
   }
 
-  const IntegerLiteral *Lit = dyn_cast<IntegerLiteral>(getInit(0));
+  const IntegerLiteral *Lit = dyn_cast<IntegerLiteral>(getInit(0)->IgnoreImplicit());
   return Lit && Lit->getValue() == 0;
 }
 

test/Sema/zero-initializer.c

@@ -7,6 +7,8 @@ struct A { int a; };
 struct B { struct A a; };
 struct C { struct B b; };
 struct D { struct C c; int n; };
+struct E { short e; };
+struct F { struct E e; int n; };
 
 int main(void)
 {
@@ -23,6 +25,9 @@ int main(void)
   struct C p = { 0 }; // no-warning
   struct C q = { 9 }; // warning suppressed for struct with single element
   struct D r = { 9 }; // expected-warning {{suggest braces around initialization of subobject}} expected-warning {{missing field 'n' initializer}}
+  struct F s = { 0 }; // no-warning
+  struct F t = { 9 }; // expected-warning {{suggest braces around initialization of subobject}} expected-warning {{missing field 'n' initializer}}
+
   f = (struct foo ) { 0 }; // no-warning
   g = (struct foo ) { 9 }; // expected-warning {{missing field 'y' initializer}}
   h = (struct foo ) { 9, 9 }; // no-warning
@@ -36,6 +41,8 @@ int main(void)
   p = (struct C) { 0 }; // no-warning
   q = (struct C) { 9 }; // warning suppressed for struct with single element
   r = (struct D) { 9 }; // expected-warning {{suggest braces around initialization of subobject}} expected-warning {{missing field 'n' initializer}}
+  s = (struct F) { 0 }; // no-warning
+  t = (struct F) { 9 }; // expected-warning {{suggest braces around initialization of subobject}} expected-warning {{missing field 'n' initializer}}
 
   return 0;
 }