[clang] Fix a crash case when reporting an uninitialized field.

[hliao]

Summary

• As the initializer list's getSyntacticForm() may return NULL, need to consider the current semantic initalizer list itself as the synatic form. Wrap that together into a new getSourceRange method.

[hliao]

Revise the formatting.

[hliao]

Rebase

clang/include/clang/AST/Expr.h

bool hadArrayRangeDesignator() const {
     return InitListExprBits.HadArrayRangeDesignator != 0;
   }
   void sawArrayRangeDesignator(bool ARD = true) {
     InitListExprBits.HadArrayRangeDesignator = ARD;
   }
 
   SourceLocation getBeginLoc() const LLVM_READONLY;
   SourceLocation getEndLoc() const LLVM_READONLY;
+  SourceRange getSourceRange() const LLVM_READONLY {
+    return SourceRange(getBeginLoc(), getEndLoc());
+  }
 
   static bool classof(const Stmt *T) {
     return T->getStmtClass() == InitListExprClass;
   }
 
   // Iterators
   child_range children() {
     const_child_range CCR = const_cast<const InitListExpr *>(this)->children();

clang/lib/Sema/SemaInit.cpp

if (Init >= NumInits || !ILE->getInit(Init)) {
 
     if (Field->getType()->isReferenceType()) {
       if (!VerifyOnly) {
         // C++ [dcl.init.aggr]p9:
         //   If an incomplete or empty initializer-list leaves a
         //   member of reference type uninitialized, the program is
         //   ill-formed.
         SemaRef.Diag(Loc, diag::err_init_reference_member_uninitialized)
-          << Field->getType()
-          << ILE->getSyntacticForm()->getSourceRange();
+            << Field->getType() << ILE->getSourceRange();
         SemaRef.Diag(Field->getLocation(),
                      diag::note_uninit_reference_member);
       }
       hadError = true;
       return;
     }
 
     ExprResult MemberInit = PerformEmptyInit(Loc, MemberEntity);

clang/test/SemaCXX/uninitialized.cpp

 template<typename T> struct Outer {
   struct Inner {
     int a = 1;
     int b;
     Inner() : b(a) {}
   };
 };
 Outer<int>::Inner outerinner;
+
+namespace crash_on_report_uninitialized_field {
+struct S {
+  union {
+    struct {
+      const int &f0;
+      const float &f1; // expected-note{{uninitialized reference member is here}}
+    };
+    double d;
+  };
+};
+void bar(struct S &s);
+void foo(int i, float f) {
+  S s = { .f0 = i }; // expected-error{{reference member of type 'const float &' uninitialized}}
+  bar(s);
+}
+}