[PATCH] avoid ICE when attempting to init a flexible array member (PR c++/79363)

[Martin Sebor <msebor at gmail dot com>]

The attached patch avoids another ICE (in addition to the already
fixed bug 72775) in flexible array member NSDMI.  To avoid code
duplication and for consistency I factored the diagnostic code
out of perform_member_init and into a new helper.

Martin

PR c++/79363 - ICE with NSDMI and array

gcc/cp/ChangeLog:

	PR c++/79363
	* init.c (maybe_reject_flexarray_init): New function.
	(perform_member_init): Call it.

gcc/testsuite/ChangeLog:

	PR c++/79363
	* g++.dg/ext/flexary12.C: Adjust.
	* g++.dg/ext/flexary20.C: Same.
	* g++.dg/ext/flexary21.C: Same.
	* g++.dg/ext/flexary22.C: New test.

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 42f1c61..c83d2eb 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -597,6 +597,33 @@ get_nsdmi (tree member, bool in_ctor)
   return init;
 }
 
+/* Diagnose the flexible array MEMBER if its INITializer is non-null
+   and return true if so.  Otherwise return false.  */
+
+static bool
+maybe_reject_flexarray_init (tree member, tree init)
+{
+  tree type = TREE_TYPE (member);
+
+  if (!init
+      || TREE_CODE (type) != ARRAY_TYPE
+      || TYPE_DOMAIN (type))
+    return false;
+
+  /* Point at the flexible array member declaration if it's initialized
+     in-class, and at the ctor if it's initialized in a ctor member
+     initializer list.  */
+  location_t loc;
+  if (DECL_INITIAL (member) == init
+      || DECL_DEFAULTED_FN (current_function_decl))
+    loc = DECL_SOURCE_LOCATION (member);
+  else
+    loc = DECL_SOURCE_LOCATION (current_function_decl);
+
+  error_at (loc, "initializer for flexible array member %q#D", member);
+  return true;
+}
+
 /* Initialize MEMBER, a FIELD_DECL, with INIT, a TREE_LIST of
    arguments.  If TREE_LIST is void_type_node, an empty initializer
    list was given; if NULL_TREE no initializer was given.  */
@@ -722,10 +749,18 @@ perform_member_init (tree member, tree init)
 	{
 	  if (init)
 	    {
-	      if (TREE_CHAIN (init))
+	      /* Check to make sure the member initializer is valid and
+		 something like a CONSTRUCTOR in: T a[] = { 1, 2 } and
+		 if it isn't, return early to avoid triggering another
+		 error below.  */
+	      if (maybe_reject_flexarray_init (member, init))
+		return;
+
+	      if (TREE_CODE (init) != TREE_LIST || TREE_CHAIN (init))
 		init = error_mark_node;
 	      else
 		init = TREE_VALUE (init);
+
 	      if (BRACE_ENCLOSED_INITIALIZER_P (init))
 		init = digest_init (type, init, tf_warning_or_error);
 	    }
@@ -800,16 +835,9 @@ perform_member_init (tree member, tree init)
 	   in that case.  */
 	init = build_x_compound_expr_from_list (init, ELK_MEM_INIT,
 						tf_warning_or_error);
-      if (TREE_CODE (type) == ARRAY_TYPE
-	  && TYPE_DOMAIN (type) == NULL_TREE
-	  && init != NULL_TREE)
-	{
-	  error_at (DECL_SOURCE_LOCATION (current_function_decl),
-		    "member initializer for flexible array member");
-	  inform (DECL_SOURCE_LOCATION (member), "%q#D initialized", member);
-	}
 
-      if (init)
+      /* Reject a member initializer for a flexible array member.  */
+      if (init && !maybe_reject_flexarray_init (member, init))
 	finish_expr_stmt (cp_build_modify_expr (input_location, decl,
 						INIT_EXPR, init,
 						tf_warning_or_error));
diff --git a/gcc/testsuite/g++.dg/ext/flexary12.C b/gcc/testsuite/g++.dg/ext/flexary12.C
index db80bf4..763ffa3 100644
--- a/gcc/testsuite/g++.dg/ext/flexary12.C
+++ b/gcc/testsuite/g++.dg/ext/flexary12.C
@@ -44,8 +44,9 @@ struct D {
   D ();
 };
 
-D::D ():    // { dg-error "member initializer for flexible array member" }
-  a ("c")   // { dg-error "incompatible types in assignment of .const char \\\[2\\\]. to .int \\\[\\\]." }
+D::D ():    // { dg-error "initializer for flexible array member" }
+  a ("c")   // the initializer also has an invalid type but emitting
+            // just the error above is sufficient
 { }
 
 
diff --git a/gcc/testsuite/g++.dg/ext/flexary20.C b/gcc/testsuite/g++.dg/ext/flexary20.C
index 2c8ab29..10a06b4 100644
--- a/gcc/testsuite/g++.dg/ext/flexary20.C
+++ b/gcc/testsuite/g++.dg/ext/flexary20.C
@@ -4,22 +4,22 @@
 
 struct S {
   int i;
-  char a[] = "foo";
-  S () {} // { dg-error "member initializer for flexible array member" }
+  char a[] = "foo";   // { dg-error "initializer for flexible array member" }
+  S () {}
 };
 
-struct T { // { dg-error "member initializer for flexible array member" }
+struct T {
   int i;
-  char a[] = "foo";
+  char a[] = "foo";   // { dg-error "initializer for flexible array member" }
 };
 
 struct U {
   int i;
-  char a[] = "foo";
+  char a[] = "foo";   // { dg-error "initializer for flexible array member" }
   U ();
 };
 
-U::U() {} // { dg-error "member initializer for flexible array member" }
+U::U() {}
 
 int
 main ()
@@ -29,17 +29,17 @@ main ()
 
 struct V {
   int i;
-  struct W { // { dg-error "member initializer for flexible array member" }
+  struct W {
     int j;
-    char a[] = "foo";
+    char a[] = "foo";   // { dg-error "initializer for flexible array member" }
   } w;
   V () {}
 };
 
 template <class T>
-struct X { // { dg-error "member initializer for flexible array member" }
+struct X {
   int i;
-  T a[] = "foo";
+  T a[] = "foo";   // { dg-error "initializer for flexible array member" }
 };
 
 void
diff --git a/gcc/testsuite/g++.dg/ext/flexary21.C b/gcc/testsuite/g++.dg/ext/flexary21.C
index 5675bf6..24d330a 100644
--- a/gcc/testsuite/g++.dg/ext/flexary21.C
+++ b/gcc/testsuite/g++.dg/ext/flexary21.C
@@ -5,11 +5,16 @@
 struct S {
   int i;
   char a[];
-  S () : a("bob") {} // { dg-error "member initializer for flexible array member" }
+  S () : a("bob") {} // { dg-error "initializer for flexible array member" }
 };
 
 struct T {
   int i;
-  char a[] = "bob";
-  T () : a("bob") {} // { dg-error "member initializer for flexible array member" }
+  char b[] = "bob";      // { dg-error "initializer for flexible array member" }
+  T () {
+    // the presence of this ctor definition elicits the error above
+    // without it the flexible array initializer would be ignored
+    // and so (unfortunately) not diagnosed
+  }
+  T (int) : b("bob") {}  // { dg-error "initializer for flexible array member" }
 };
diff --git a/gcc/testsuite/g++.dg/ext/flexary22.C b/gcc/testsuite/g++.dg/ext/flexary22.C
new file mode 100644
index 0000000..041f024
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/flexary22.C
@@ -0,0 +1,29 @@
+// PR c++/79363 - ICE with NSDMI and array
+// { dg-do compile { target c++11 } }
+// { dg-options -Wno-pedantic }
+
+struct A
+{
+  int i;
+  int a[] = { };   // { dg-error "initializer for flexible array member" }
+} a;
+
+struct B
+{
+  int i;
+  char a[] { "abc" };   // { dg-error "initializer for flexible array member" }
+} b;
+
+struct C
+{
+  int i;
+  char a[];
+  C (): a ("def") { }   // { dg-error "initializer for flexible array member" }
+} c;
+
+struct D
+{
+  struct X { };
+  int i;
+  X x[] = { };   // { dg-error "initializer for flexible array member" }
+} d;