[clang] Check `expr` inside `InitListChecker::UpdateStructuredListElement()`

- Prevent nullptr-deference at try to emit warning for invalid `expr`
- Simplify `InitListChecker::UpdateStructuredListElement()` usages. We do not need to check `expr` and increment `StructuredIndex` (for invalid `expr`) before the call anymore.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D85193

clang/lib/Sema/SemaInit.cpp

@@ -1585,10 +1585,7 @@ void InitListChecker::CheckScalarType(const InitializedEntity &Entity,
       IList->setInit(Index, ResultExpr);
     }
   }
-  if (hadError)
-    ++StructuredIndex;
-  else
-    UpdateStructuredListElement(StructuredList, StructuredIndex, ResultExpr);
+  UpdateStructuredListElement(StructuredList, StructuredIndex, ResultExpr);
   ++Index;
 }
 
@@ -1643,10 +1640,7 @@ void InitListChecker::CheckReferenceType(const InitializedEntity &Entity,
   if (!VerifyOnly && expr)
     IList->setInit(Index, expr);
 
-  if (hadError)
-    ++StructuredIndex;
-  else
-    UpdateStructuredListElement(StructuredList, StructuredIndex, expr);
+  UpdateStructuredListElement(StructuredList, StructuredIndex, expr);
   ++Index;
 }
 
@@ -1697,11 +1691,7 @@ void InitListChecker::CheckVectorType(const InitializedEntity &Entity,
           IList->setInit(Index, ResultExpr);
         }
       }
-      if (hadError)
-        ++StructuredIndex;
-      else
-        UpdateStructuredListElement(StructuredList, StructuredIndex,
-                                    ResultExpr);
+      UpdateStructuredListElement(StructuredList, StructuredIndex, ResultExpr);
       ++Index;
       return;
     }
@@ -3100,8 +3090,12 @@ void InitListChecker::UpdateStructuredListElement(InitListExpr *StructuredList,
 
   if (Expr *PrevInit = StructuredList->updateInit(SemaRef.Context,
                                                   StructuredIndex, expr)) {
-    // This initializer overwrites a previous initializer. Warn.
-    diagnoseInitOverride(PrevInit, expr->getSourceRange());
+    // This initializer overwrites a previous initializer.
+    // No need to diagnose when `expr` is nullptr because a more relevant
+    // diagnostic has already been issued and this diagnostic is potentially
+    // noise.
+    if (expr)
+      diagnoseInitOverride(PrevInit, expr->getSourceRange());
   }
 
   ++StructuredIndex;

clang/test/Sema/init-invalid-struct-array.c

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only
+
+struct S {
+  Unknown u; // expected-error {{unknown type name 'Unknown'}}
+  int i;
+};
+// Should not crash
+struct S s[] = {[0].i = 0, [1].i = 1, {}};