Hi!
Even in C23/C2Y any initialization of flexible array member is still
invalid, so we should emit a pedwarn on it. But we no longer do for
initialization with {}. The reason is that for C17 and earlier,
we already emitted a pedwarn on the {} initializer and so emitting
another pedwarn on the flexible array member initialization would
be diagnosing the same thing multiple times.
In C23 we no longer pedwarn on {}, it is standard.
The following patch arranges a pedwarning for that for C23+, so that
at least one pedwarning is emitted.
So that we don't "regress" from C17 to C23 on nested flexible array
member initialization with no -pedantic/-pedantic-errors/-Wpedantic,
the patch emits even the
initialization of flexible array member in a nested context
diagnostic as pedwarn in the {} case, after all, it doesn't cause
much trouble, we just ignore it like before, it wouldn't initialize
anything.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2025-03-19 Jakub Jelinek <ja...@redhat.com>
PR c/119350
* c-typeck.cc (pop_init_level): Don't ignore empty brackets for
flag_isoc23, still set constructor_type to NULL in that case but
emit a pedwarn_init in that case.
* gcc.dg/pr119350-1.c: New test.
* gcc.dg/pr119350-2.c: New test.
* gcc.dg/pr119350-3.c: New test.
--- gcc/c/c-typeck.cc.jj 2025-03-12 21:56:44.217767602 +0100
+++ gcc/c/c-typeck.cc 2025-03-19 00:22:34.094330536 +0100
@@ -10274,24 +10274,29 @@ pop_init_level (location_t loc, int impl
&& !TYPE_MAX_VALUE (TYPE_DOMAIN (constructor_type)))
{
/* Silently discard empty initializations. The parser will
- already have pedwarned for empty brackets. */
+ already have pedwarned for empty brackets for C17 and earlier. */
if (integer_zerop (constructor_unfilled_index))
constructor_type = NULL_TREE;
- else
+ if (constructor_type || flag_isoc23)
{
- gcc_assert (!TYPE_SIZE (constructor_type));
+ gcc_assert (!constructor_type || !TYPE_SIZE (constructor_type));
- if (constructor_depth > 2)
+ if (constructor_depth <= 2)
+ pedwarn_init (loc, OPT_Wpedantic,
+ "initialization of a flexible array member");
+ else if (constructor_type)
error_init (loc, "initialization of flexible array member "
"in a nested context");
else
pedwarn_init (loc, OPT_Wpedantic,
- "initialization of a flexible array member");
+ "initialization of flexible array member "
+ "in a nested context");
/* We have already issued an error message for the existence
of a flexible array member not at the end of the structure.
Discard the initializer so that we do not die later. */
- if (DECL_CHAIN (constructor_fields) != NULL_TREE
+ if (constructor_type
+ && DECL_CHAIN (constructor_fields) != NULL_TREE
&& (!p->type || TREE_CODE (p->type) != UNION_TYPE))
constructor_type = NULL_TREE;
}
--- gcc/testsuite/gcc.dg/pr119350-1.c.jj 2025-03-18 21:22:54.450558554
+0100
+++ gcc/testsuite/gcc.dg/pr119350-1.c 2025-03-18 21:22:54.450558554 +0100
@@ -0,0 +1,14 @@
+/* PR c/119350 */
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -pedantic-errors" } */
+
+struct S { int a; int b[]; };
+struct T { struct S c; }; /* { dg-error "invalid use of
structure with flexible array member" } */
+struct S d = { 1, {} }; /* { dg-error
"initialization of a flexible array member" } */
+struct S e = { 1, { 2 } }; /* { dg-error "initialization
of a flexible array member" } */
+struct S f = { .a = 1, .b = {} }; /* { dg-error "initialization
of a flexible array member" } */
+struct S g = { .a = 1, .b = { 2 } }; /* { dg-error "initialization
of a flexible array member" } */
+struct T h = { { 1, {} } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
+struct T i = { { 1, { 2 } } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
+struct T j = { .c = { .a = 1, .b = {} } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
+struct T k = { .c = { .a = 1, .b = { 2 } } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
--- gcc/testsuite/gcc.dg/pr119350-2.c.jj 2025-03-18 21:22:54.450558554
+0100
+++ gcc/testsuite/gcc.dg/pr119350-2.c 2025-03-19 00:24:33.735762508 +0100
@@ -0,0 +1,14 @@
+/* PR c/119350 */
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -Wpedantic" } */
+
+struct S { int a; int b[]; };
+struct T { struct S c; }; /* { dg-warning "invalid use of
structure with flexible array member" } */
+struct S d = { 1, {} }; /* { dg-warning
"initialization of a flexible array member" } */
+struct S e = { 1, { 2 } }; /* { dg-warning "initialization
of a flexible array member" } */
+struct S f = { .a = 1, .b = {} }; /* { dg-warning "initialization
of a flexible array member" } */
+struct S g = { .a = 1, .b = { 2 } }; /* { dg-warning "initialization
of a flexible array member" } */
+struct T h = { { 1, {} } }; /* { dg-warning "initialization
of flexible array member in a nested context" } */
+struct T i = { { 1, { 2 } } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
+struct T j = { .c = { .a = 1, .b = {} } }; /* { dg-warning "initialization
of flexible array member in a nested context" } */
+struct T k = { .c = { .a = 1, .b = { 2 } } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
--- gcc/testsuite/gcc.dg/pr119350-3.c.jj 2025-03-18 21:22:54.451558540
+0100
+++ gcc/testsuite/gcc.dg/pr119350-3.c 2025-03-19 00:25:10.859275972 +0100
@@ -0,0 +1,14 @@
+/* PR c/119350 */
+/* { dg-do compile } */
+/* { dg-options "-std=c23 -Wc11-c23-compat" } */
+
+struct S { int a; int b[]; };
+struct T { struct S c; };
+struct S d = { 1, {} }; /* { dg-warning "ISO C
forbids empty initializer braces before C23" } */
+struct S e = { 1, { 2 } };
+struct S f = { .a = 1, .b = {} }; /* { dg-warning "ISO C forbids
empty initializer braces before C23" } */
+struct S g = { .a = 1, .b = { 2 } };
+struct T h = { { 1, {} } }; /* { dg-warning "ISO C forbids
empty initializer braces before C23" } */
+struct T i = { { 1, { 2 } } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
+struct T j = { .c = { .a = 1, .b = {} } }; /* { dg-warning "ISO C forbids
empty initializer braces before C23" } */
+struct T k = { .c = { .a = 1, .b = { 2 } } }; /* { dg-error "initialization
of flexible array member in a nested context" } */
Jakub
