Fixed the bug that a union type containing a struct with a flexible array member was accepted as a struct member or array element type.

src/cc65/declare.c

@@ -517,7 +517,8 @@ static void CheckArrayElementType (const Type* T)
                     return;
                 }
             } else {
-                if (IsTypeStruct (T)) {
+                /* Elements cannot contain flexible array members themselves */
+                if (IsClassStruct (T)) {
                     SymEntry* TagEntry = GetESUTagSym (T);
                     if (TagEntry && SymHasFlexibleArrayMember (TagEntry)) {
                         Error ("Invalid use of struct with flexible array member");
@@ -1202,11 +1203,9 @@ static SymEntry* ParseStructSpec (const char* Name, unsigned* DSFlags)
                     if (TagEntry && SymHasFlexibleArrayMember (TagEntry)) {
                         Field->Flags |= SC_HAVEFAM;
                         Flags        |= SC_HAVEFAM;
-                        if (IsTypeStruct (Decl.Type)) {
                         Error ("Invalid use of struct with flexible array member");
                     }
                 }
-                }
 
                 if (!FlexibleMember) {
                     StructSize += SizeOf (Decl.Type);

test/err/bug2016-fam-member.c

@@ -5,7 +5,12 @@ typedef struct x {
     int b[];    /* Ok: Flexible array member can be last */
 } x;
 
+typedef union u {
+    int a;
+    x   x;      /* Ok: Union member can contain flexible array member */
+} u;
+
 struct y {
-    x   x;      /* Not ok: Contains flexible array member */
+    u   u;      /* Not ok: Contains union that contains flexible array member */
     int a;
 };

test/err/bug2017-fam-element.c

@@ -1,9 +1,13 @@
 /* Bug #2017 - cc65 erroneously allows arrays of structs with flexible array members */
 
-struct z {
+typedef struct x {
     int a;
-    int c;
+    int b[];    /* Ok: Flexible array member can be last */
-    int b[];
+} x;
-};
 
-struct z y[3];          /* Should be an error */
+typedef union u {
+    int a;
+    x   x;      /* Ok: Union member can contain flexible array member */
+} u;
+
+union u y[3];  /* Should be an error */

test/val/fam.c

@@ -0,0 +1,31 @@
+/* Bug #2016 and #2017 - flexible array members */
+
+typedef struct {
+    int a;
+    int b[];        /* Ok: Flexible array member can be last */
+} X;
+
+typedef union {
+    X   x;          /* Ok: Contains flexible array member */
+    int a;
+} U;
+
+typedef struct {
+    struct {
+        int a;
+    };
+    int b[];    /* Ok: Flexible array member can be last */
+} Y;
+
+X x;
+U u;
+Y y;
+
+_Static_assert(sizeof x == sizeof (int), "sizeof x != sizeof (int)");
+_Static_assert(sizeof u == sizeof (int), "sizeof u != sizeof (int)");
+_Static_assert(sizeof y == sizeof (int), "sizeof y != sizeof (int)");
+
+int main(void)
+{
+    return 0;
+}