Re: [PATCH v8 1/5] Provide counted_by attribute to flexible array member field (PR108896)

[Joseph Myers <josmyers@redhat.com>]

On Wed, 10 Apr 2024, Qing Zhao wrote:

> A stupid question first, the same scope means the same file? (Or same function)

struct X { int a; };
struct X { int a; };

is an example of the same scope (file scope, in this case).  The 
structures must have the same contents (in an appropriate sense) and are 
then considered the same type.

struct X { int a; };
void f() { struct X { int a; }; }

is not the same scope - but C23 makes the types compatible (not the same).  
It's OK to have incompatible types with the same tag in different scopes 
as well

struct X { int a; };
void f() { struct X { long b; }; }

but if you use them in a way requiring compatibility, then the contents 
must be compatible

struct X { int a; } v;
void f() { struct X { int a; } *p = &v; }

> Is there a testing case for this feature in current GCC source tree I can take a look? (and
> Then I can use it to construct the new testing case for the counted-by attribute).

See gcc.dg/c23-tag-*.c for many tests of different cases involving the tag 
compatibility rules (and gcc.dg/gnu23-tag-* where GNU extensions are 
involved).

-- 
Joseph S. Myers
josmyers@redhat.com