Filter non-BuildTarget paths from extra_paths

[tristan957]

In Postgres, we saw an issue[0] where translation targets (custom targets) parent directories were being added to PATH on Windows. Generally, this would not be a problem. However, Windows limits the length of environment variables. Given the amount of translation targets in Postgres, this led to PATH being longer than what Windows allows and tests would fail to run.

By filtering non-BuildTarget dependencies, we can mitigate the problem. Windows searches for DLLs and executables on PATH, so because we can assume that non-BuildTarget dependencies are not going to be DLLs or executables, we can safely filter them out of the extra_paths list.

Link: https://www.postgresql.org/message-id/CAD5tBcJXAX8bz5q9ngE4znvVLiXaPO89D0yTFhJgEPrPyT-Erw@mail.gmail.com [0]

[tristan957]

I believe based on discussion in Matrix that Luca is also suggesting that we also include ExternalProgram and filter StaticLibrary. I think that makes sense.

[dcbaker]

Does this break the external_project module and any CustomTarget that points to an executable of some kind, say like something wrapping cargo build?

[tristan957]

Does this break the external_project module and any CustomTarget that points to an executable of some kind, say like something wrapping cargo build?

I was thinking about this, and I guess it would. I'm not sure the best way to work around that.

[tristan957]

In Postgres, the things that are causing us trouble are the .mo CustomTargets output by i18n.gettext().

[lb90]

I was thinking something like that:

diff --git a/mesonbuild/backend/backends.py b/mesonbuild/backend/backends.py
index 21cc8bb0a..81acf9cbb 100644
--- a/mesonbuild/backend/backends.py
+++ b/mesonbuild/backend/backends.py
@@ -1216,7 +1216,21 @@ class Backend:
                 extra_bdeps: T.List[build.BuildTargetTypes] = []
                 if isinstance(exe, build.CustomTarget):
                     extra_bdeps = list(exe.get_transitive_build_target_deps())
-                extra_bdeps.extend(t.depends)
+
+                # Don't include the entire t.depends to avoid hitting limmits
+                # on the environment block size (about 32k characters). See
+                # https://github.com/mesonbuild/meson/issues/16010
+                for d in t.depends:
+                    if isinstance(d, (build.BuildTarget, build.Executable)):
+                        extra_bdeps.add(d)
+                        for l in d.get_all_link_deps():
+                            if isinstance(l, build.SharedLibrary):
+                                extra_bdeps.add(l)
+                    elif isinstance(d, build.LocalProgram):
+                        pass # TODO
+                    elif isinstance(d, programs.ExternalProgram):
+                        extra_bdeps.add(d)
+
                 extra_bdeps.extend(a for a in t.cmd_args if isinstance(a, build.BuildTarget))
                 extra_paths = self.determine_windows_extra_paths(exe, extra_bdeps)
             else:

Maybe we can call links_dynamically() (introduced in #12059)

[lb90]

Does this break the external_project module and any CustomTarget that points to an executable of some kind, say like something wrapping cargo build?

I'd just go for a middle ground: If a depend is something that Meson knows it's a DLL or program, add it to PATH automatically; for anything else it's up to the user.

In general you never can tell. For example, a depend may be a Python module generated via a Custom target. In that case you don't want to add to PATH, but to PYTHONPATH. Only the user knows

Note: we're already filtering on UNIX: https://github.com/mesonbuild/meson/blob/master/mesonbuild/backend/backends.py#L1254