Re: meson's in-tree libpq header search order vs -Dextra_include_dirs

On Sun Feb 2, 2025 at 6:29 PM CST, Thomas Munro wrote:
> When I use configure/make and --with-includes=/usr/local/include, I
> see compile lines like this:
>
> ... -I../../src/interfaces/libpq -I../../src/include  -I/usr/local/include ...
>
> That's important, because if I happen to have libpq headers installed
> on the system I don't want to be confused by them.  Yet meson's
> -Dextra_include_dirs=/usr/local/include compiles like this:
>
> ... -I../src/include -I/usr/local/include -Isrc/interfaces/libpq ...
>
> ... which gives me errors due to the v16 headers I happen to have installed:
>
> ../src/fe_utils/connect_utils.c:164:3: error: unknown type name
> 'PGcancelConn'; did you mean 'PGcancel'?
>   164 |                 PGcancelConn *cancelConn = PQcancelCreate(conn);
>
> I guess this affects Macs, BSDs and a few lesser used Linux distros
> that put optional packages outside the base system and default search
> paths.  Perhaps you can see this on everything-goes-into-base-system
> distros if you redundantly say -Dextra_include_dirs=/usr/include; I
> didn't check if that is true, it wouldn't be if meson is opinionated
> enough to remove it.

What is the benefit of -Dextra_include_dirs when you could use -Dc_flags
or CFLAGS to specify extra include directories? If you tried either of
those as an alternative, would they fix the issue? The existence of the
option goes all the way back to the initial commit of the meson port, so
I presume it exists to mirror --with-includes, but why does that exist?

--
Tristan Partin
Databricks (https://databricks.com)