Re: meson: avoid PATH bloat from NLS .mo targets in tmp_install test setup

On Wed Jul 15, 2026 at 8:49 PM UTC, Tristan Partin wrote:
> On Wed Jul 15, 2026 at 8:44 PM UTC, Andrew Dunstan wrote:
>> On Wed, Jul 15, 2026 at 12:30 PM Tristan Partin <tristan(at)partin(dot)io> wrote:
>>
>>> On Tue Jul 14, 2026 at 9:24 PM UTC, Andrew Dunstan wrote:
>>> > Hi
>>> >
>>> > While setting up a Windows/MSVC buildfarm animal with NLS enabled, the
>>> > meson 'tmp_install' and 'initdb_cache' setup tests failed immediately
>>> > with exit status 1 and no stdout/stderr at all.
>>> >
>>> > With a little help from Claude, I (eventually) found this diagnosis and
>>> > solution:
>>> >
>>> > The root cause turned out to be in meson itself, not in our meson.build.
>>> > On Windows, determine_windows_extra_paths() in
>>> > mesonbuild/backend/backends.py builds a test's PATH by walking every
>>> > target passed via that test's 'depends:' kwarg (extra_bdeps) and adding
>>> > each one's build directory unconditionally, with no check for whether
>>> > the target actually produces a DLL. That's fine when 'depends:' lists a
>>> > handful of real link dependencies, but the 'tmp_install' test depends on
>>> > installed_targets, which includes nls_mo_targets - one custom_target per
>>> > locale/domain of compiled .mo catalogs. With NLS enabled that's several
>>> > hundred targets, none of them DLLs, none of them ever looked up via
>>> > PATH, and each one still gets its own entry.
>>> >
>>> > In our case this inflated PATH to ~39000 characters across 584 entries
>>> > (448 of them po/*/LC_MESSAGES directories), comfortably past practical
>>> > Windows environment-variable/command-line length limits, which is why
>>> > the test failed silently - the failure happens before the child process
>>> > gets a chance to produce any output.
>>> >
>>> > I think this is arguably a meson bug (determine_windows_extra_paths()
>>> > should filter extra_bdeps the same way it already filters a test
>>> > executable's own link dependencies), but regardless of whether that
>>> > gets fixed upstream, we can sidestep it on our end cheaply: depend on a
>>> > trivial stamp custom_target instead of installed_targets directly. Its
>>> > own 'depends:' still forces installed_targets to build first, so build
>>> > ordering is unaffected, but since a custom_target is not a
>>> > build.BuildTarget, meson doesn't recurse into its dependencies when
>>> > computing the test PATH - it contributes at most one harmless directory
>>> > instead of hundreds.
>>> >
>>> > I initially tried wrapping installed_targets in an alias_target()
>>> > instead, which would avoid the recursion the same way, but test()'s
>>> > 'depends:' kwarg is typechecked to only accept
>>> > BuildTarget | CustomTarget | CustomTargetIndex and rejects AliasTarget
>>> > outright:
>>> >
>>> > meson.build:NNNN:0: ERROR: test keyword argument 'depends' was of
>>> > type array[AliasTarget] but should have been type
>>> > array[BuildTarget | CustomTarget | CustomTargetIndex]
>>> >
>>> > The attached patch uses a custom_target instead, which satisfies that
>>> > type check.
>>> >
>>> > Tested on Windows/MSVC (meson 1.11.1), building with -Dnls=enabled:
>>> >
>>> > before: tmp_install test PATH = 39193 chars, 584 entries, 448
>>> > LC_MESSAGES - tmp_install and initdb_cache setup tests FAIL
>>> > (exit status 1, no output)
>>> > after: tmp_install test PATH = 2189 chars, 43 entries, 0
>>> > LC_MESSAGES - all three setup tests (tmp_install,
>>> > install_test_files, initdb_cache) OK
>>> >
>>> > I did not attempt to fix the same class of problem for any other test
>>> > in the tree - this patch only touches the one setup test that was
>>> > actually failing for us. If there's interest, the same technique could
>>> > presumably be applied wherever else a test's 'depends:' pulls in a
>>> > large target list.
>>>
>>> Hey Andrew,
>>>
>>> I took some time to raise this issue with the Meson team in their
>>> Matrix/IRC channel. I'll see if the discussion goes anywhere.
>>>
>>> As for the fix and the results, they look good to me. I couldn't
>>> identify any other problems where this could be an issue, so this seems
>>> like a one-off. Did you notice any other problems? I only noticed
>>> installed_targets depended on in tmp_install and install-quiet.
>>>
>>
>>
>> I should have mentioned that I raised an issue at <
>> https://github.com/mesonbuild/meson/issues/16010>
>
> Thanks! Currently discussing potential solutions.

I posted a PR[0] to fix this. Just waiting on review. Thanks for your
initial investigation.

[0]: https://github.com/mesonbuild/meson/pull/16039

--
Tristan Partin
PostgreSQL Contributors Team
AWS (https://aws.amazon.com)