[Clang] Fix crash when emitting diagnostic for out of order designate…

…d initializers in C++

In C++ we are not allowed to use designated initializers to initialize fields
out of order. In some cases when diagnosing this we are crashing because we are
not indexing correctly and therefore going out of bounds.

This fixes: #63605

Differential Revision: https://reviews.llvm.org/D154675

clang/docs/ReleaseNotes.rst

@@ -695,6 +695,9 @@ Bug Fixes to C++ Support
 - Fix handling of using-declarations in the init statements of for
   loop declarations.
   (`#63627 <https://github.com/llvm/llvm-project/issues/63627>`_)
+- Fix crash when emitting diagnostic for out of order designated initializers
+  in C++.
+  (`#63605 <https://github.com/llvm/llvm-project/issues/63605>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaInit.cpp

@@ -2847,7 +2847,7 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
         SemaRef.Diag(DIE->getBeginLoc(), diag::ext_designated_init_reordered)
             << KnownField << PrevField << DIE->getSourceRange();
 
-        unsigned OldIndex = NumBases + PrevField->getFieldIndex();
+        unsigned OldIndex = StructuredIndex - 1;
         if (StructuredList && OldIndex <= StructuredList->getNumInits()) {
           if (Expr *PrevInit = StructuredList->getInit(OldIndex)) {
             SemaRef.Diag(PrevInit->getBeginLoc(),
@@ -2951,8 +2951,12 @@ InitListChecker::CheckDesignatedInitializer(const InitializedEntity &Entity,
     // If this the first designator, our caller will continue checking
     // the rest of this struct/class/union subobject.
     if (IsFirstDesignator) {
+      if (Field != RD->field_end() && Field->isUnnamedBitfield())
+        ++Field;
+
       if (NextField)
         *NextField = Field;
+
       StructuredIndex = FieldIndex;
       return false;
     }

clang/test/SemaCXX/cxx2a-initializer-aggregates.cpp

@@ -63,7 +63,7 @@ C c = {
   .x = 1, // override-note {{previous}}
   .x = 1, // override-error {{overrides prior initialization}} override-note {{previous}}
   .y = 1, // override-note {{previous}}
-  .y = 1, // override-error {{overrides prior initialization}}
+  .y = 1, // override-error {{overrides prior initialization}} // reorder-note {{previous initialization for field 'y' is here}}
   .x = 1, // reorder-error {{declaration order}} override-error {{overrides prior initialization}} override-note {{previous}}
   .x = 1, // override-error {{overrides prior initialization}}
 };
@@ -177,3 +177,43 @@ namespace no_unwrap {
     h({.a = 1});
   }
 }
+
+namespace GH63605 {
+struct A  {
+  unsigned x;
+  unsigned y;
+  unsigned z;
+};
+
+struct B {
+  unsigned a;
+  unsigned b;
+};
+
+struct : public A, public B {
+  unsigned : 2;
+  unsigned a : 6;
+  unsigned : 1;
+  unsigned b : 6;
+  unsigned : 2;
+  unsigned c : 6;
+  unsigned d : 1;
+  unsigned e : 2;
+} data = {
+  {.z=0,
+         // pedantic-note@-1 {{first non-designated initializer is here}}
+         // reorder-note@-2 {{previous initialization for field 'z' is here}}
+   .y=1, // reorder-error {{field 'z' will be initialized after field 'y'}}
+         // reorder-note@-1 {{previous initialization for field 'y' is here}}
+   .x=2}, // reorder-error {{field 'y' will be initialized after field 'x'}}
+  {.b=3,  // reorder-note {{previous initialization for field 'b' is here}}
+   .a=4}, // reorder-error {{field 'b' will be initialized after field 'a'}}
+    .e = 1, // reorder-note {{previous initialization for field 'e' is here}}
+            // pedantic-error@-1 {{mixture of designated and non-designated initializers in the same initializer list is a C99 extension}}
+    .d = 1, // reorder-error {{field 'e' will be initialized after field 'd'}}
+            // reorder-note@-1 {{previous initialization for field 'd' is here}}
+    .c = 1, // reorder-error {{field 'd' will be initialized after field 'c'}} // reorder-note {{previous initialization for field 'c' is here}}
+    .b = 1, // reorder-error {{field 'c' will be initialized after field 'b'}} // reorder-note {{previous initialization for field 'b' is here}}
+    .a = 1, // reorder-error {{field 'b' will be initialized after field 'a'}}
+};
+}