https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100125
Bug ID: 100125
Summary: -Wunused-macros generated while should be ignored; if
undef is seen?
Product: gcc
Version: 10.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: preprocessor
Assignee: unassigned at gcc dot gnu.org
Reporter: gcc at behdad dot org
Target Milestone: ---
We're facing this in HarfBuzz. I narrowed down the bug to this:
Works:
```c++
#pragma GCC diagnostic ignored "-Wunused-macros"
#define A B
```
$ g++ a.cc -c -Wunused-macros
(fine; no warning)
But if I add an `undef` to that file:
```c++
#pragma GCC diagnostic ignored "-Wunused-macros"
#define A B
#undef A
```
$ g++ a.cc -c -Wunused-macros
a.cc:3: warning: macros "A" is not used [-Wunused-macros]
3 | #define A B
Am I missing something?
