PR46255: Fix field diagnostics for C records with anonymous members.

The ParseStructUnionBody function was separately keeping track of the
field decls for historical reasons, however the "ActOn" functions add
the field to the RecordDecl anyway.

The "ParseStructDeclaration" function, which handles parsing fields
didn't have a way of handling what happens on an anonymous field, and
changing it would alter a large amount of objc code, so I chose instead
to implement this by just filling the FieldDecls vector with the actual
FieldDecls that were successfully added to the recorddecl .

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -5713,8 +5713,9 @@ def ext_flexible_array_union_gnu : Extension<
 def err_flexible_array_not_at_end : Error<
   "flexible array member %0 with type %1 is not at the end of"
   " %select{struct|interface|union|class|enum}2">;
-def err_objc_variable_sized_type_not_at_end : Error<
-  "field %0 with variable sized type %1 is not at the end of class">;
+def err_objc_variable_sized_type_not_at_end
+    : Error<"%select{field %1|unnamed field}0 with variable sized type %2 is "
+            "not at the end of class">;
 def note_next_field_declaration : Note<
   "next field declaration is here">;
 def note_next_ivar_declaration : Note<

clang/include/clang/Parse/Parser.h

@@ -2333,7 +2333,7 @@ private:
                           AccessSpecifier AS, DeclSpecContext DSC);
   void ParseEnumBody(SourceLocation StartLoc, Decl *TagDecl);
   void ParseStructUnionBody(SourceLocation StartLoc, DeclSpec::TST TagType,
-                            Decl *TagDecl);
+                            RecordDecl *TagDecl);
 
   void ParseStructDeclaration(
       ParsingDeclSpec &DS,

clang/lib/Parse/ParseDecl.cpp

@@ -4249,7 +4249,7 @@ void Parser::ParseStructDeclaration(
 /// [OBC]   '@' 'defs' '(' class-name ')'
 ///
 void Parser::ParseStructUnionBody(SourceLocation RecordLoc,
-                                  DeclSpec::TST TagType, Decl *TagDecl) {
+                                  DeclSpec::TST TagType, RecordDecl *TagDecl) {
   PrettyDeclStackTraceEntry CrashInfo(Actions.Context, TagDecl, RecordLoc,
                                       "parsing struct/union body");
   assert(!getLangOpts().CPlusPlus && "C++ declarations not supported");
@@ -4261,8 +4261,6 @@ void Parser::ParseStructUnionBody(SourceLocation RecordLoc,
   ParseScope StructScope(this, Scope::ClassScope|Scope::DeclScope);
   Actions.ActOnTagStartDefinition(getCurScope(), TagDecl);
 
-  SmallVector<Decl *, 32> FieldDecls;
-
   // While we still have something to read, read the declarations in the struct.
   while (!tryParseMisplacedModuleImport() && Tok.isNot(tok::r_brace) &&
          Tok.isNot(tok::eof)) {
@@ -4314,7 +4312,6 @@ void Parser::ParseStructUnionBody(SourceLocation RecordLoc,
             Actions.ActOnField(getCurScope(), TagDecl,
                                FD.D.getDeclSpec().getSourceRange().getBegin(),
                                FD.D, FD.BitfieldSize);
-        FieldDecls.push_back(Field);
         FD.complete(Field);
       };
 
@@ -4338,7 +4335,6 @@ void Parser::ParseStructUnionBody(SourceLocation RecordLoc,
       SmallVector<Decl *, 16> Fields;
       Actions.ActOnDefs(getCurScope(), TagDecl, Tok.getLocation(),
                         Tok.getIdentifierInfo(), Fields);
-      FieldDecls.insert(FieldDecls.end(), Fields.begin(), Fields.end());
       ConsumeToken();
       ExpectAndConsume(tok::r_paren);
     }
@@ -4364,6 +4360,9 @@ void Parser::ParseStructUnionBody(SourceLocation RecordLoc,
   // If attributes exist after struct contents, parse them.
   MaybeParseGNUAttributes(attrs);
 
+  SmallVector<Decl *, 32> FieldDecls(TagDecl->field_begin(),
+                                     TagDecl->field_end());
+
   Actions.ActOnFields(getCurScope(), RecordLoc, TagDecl, FieldDecls,
                       T.getOpenLocation(), T.getCloseLocation(), attrs);
   StructScope.Exit();

clang/lib/Parse/ParseDeclCXX.cpp

@@ -1964,7 +1964,7 @@ void Parser::ParseClassSpecifier(tok::TokenKind TagTokKind,
       Decl *D =
           SkipBody.CheckSameAsPrevious ? SkipBody.New : TagOrTempResult.get();
       // Parse the definition body.
-      ParseStructUnionBody(StartLoc, TagType, D);
+      ParseStructUnionBody(StartLoc, TagType, cast<RecordDecl>(D));
       if (SkipBody.CheckSameAsPrevious &&
           !Actions.ActOnDuplicateDefinition(DS, TagOrTempResult.get(),
                                             SkipBody)) {

clang/test/Sema/struct-decl.c

@@ -69,3 +69,44 @@ void test_hiding() {
 
 struct PreserveAttributes {};
 typedef struct __attribute__((noreturn)) PreserveAttributes PreserveAttributes_t; // expected-warning {{'noreturn' attribute only applies to functions and methods}}
+
+// PR46255
+struct FlexibleArrayMem {
+  int a;
+  int b[];
+};
+
+struct FollowedByNamed {
+  struct FlexibleArrayMem a; // expected-warning {{field 'a' with variable sized type 'struct FlexibleArrayMem' not at the end of a struct or class is a GNU extension}}
+  int i;
+};
+
+struct FollowedByUnNamed {
+  struct FlexibleArrayMem a; // expected-warning {{field 'a' with variable sized type 'struct FlexibleArrayMem' not at the end of a struct or class is a GNU extension}}
+  struct {
+    int i;
+  };
+};
+
+struct InAnonymous {
+  struct { // expected-warning-re {{field '' with variable sized type 'struct InAnonymous::(anonymous at {{.+}})' not at the end of a struct or class is a GNU extension}}
+
+    struct FlexibleArrayMem a;
+  };
+  int i;
+};
+struct InAnonymousFollowedByAnon {
+  struct { // expected-warning-re {{field '' with variable sized type 'struct InAnonymousFollowedByAnon::(anonymous at {{.+}})' not at the end of a struct or class is a GNU extension}}
+
+    struct FlexibleArrayMem a;
+  };
+  struct {
+    int i;
+  };
+};
+
+// This is the behavior in C++ as well, so making sure we reproduce it here.
+struct InAnonymousFollowedByEmpty {
+  struct FlexibleArrayMem a; // expected-warning {{field 'a' with variable sized type 'struct FlexibleArrayMem' not at the end of a struct or class is a GNU extension}}
+  struct {};
+};