Any way to force buildtype for compiler.preprocess?

[tagoh]

Hi,

I have a few content in meson.build which preprocess something. It basically works but it doesn't when giving -g3 in CFLAGS and preprocessing with gcc because gcc embeds few definitions inline:

$ diff -u <(gcc -E /usr/include/stdio.h) <(gcc -E -g3 /usr/include/stdio.h) | head
--- /dev/fd/63  2025-01-29 10:37:54.697944607 +0900
+++ /dev/fd/62  2025-01-29 10:37:54.697944607 +0900
@@ -1,66 +1,1474 @@
 # 0 "/usr/include/stdio.h"
+# 1 "/tmp/"
 # 0 "<built-in>"
+#define __STDC__ 1
+# 0 "<built-in>"
+#define __STDC_VERSION__ 202311L
+# 0 "<built-in>"
$ diff -u <(clang -E /usr/include/stdio.h) <(clang -E -g3 /usr/include/stdio.h) | head
$ 

and it causes the redefinition error.

I could worked this around like compiler.preprocess(..., compile_args: '-g0') but I'm not sure if it is really portable way.
What is the best way to build such case without any problems?

[thesamesam]

Some context here is:

• https://gitlab.freedesktop.org/fontconfig/fontconfig/-/issues/335
• https://gitlab.freedesktop.org/fontconfig/fontconfig/-/issues/436
• https://gitlab.haskell.org/ghc/ghc/-/merge_requests/12569 (non-meson)

GCC documents that macro definitions are included inline with -g3:

Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3.

It appears that this is actually a Clang bug in that it doesn't map -g3 to its -fdebug-macro option, per llvm/llvm-project#14524, so we should be seeing this behaviour with both GCC and Clang, and it's a bug that we don't with Clang.

But as for compiler.preprocess, I suppose we want to always add -g0 or -fno-debug-macro (?) if supported by the compiler.

[dcbaker]

Given that Clang is saying this is a bug, then we should go for one of those two options.

[thesamesam]

OK, mine.