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

On Sun Oct 4, 2026 at 12:52 PM UTC, Andrew Dunstan wrote:
>
> On 2026-09-21 Mo 5:50 PM, Tristan Partin wrote:
>> On Wed Jul 29, 2026 at 11:28 AM CDT, Tristan Partin wrote:
>>> 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
>> I ended up using a different solution, but this is now fixed[1] in
>> Meson, and will be released in 1.13.0.
>>
>> [1]: https://github.com/mesonbuild/meson/pull/16039
>
>
> Hi Tristan
>
>
> Thanks for following up. Meanwhile I intend to apply the fix to
> meson.build I originally proposed, which is fairly harmless and small,
> so we don't have to wait for everyone to catch up to the latest meson
> (which isn't out yet anyway).

Yep, makes complete sense to me. One thing that you could do is guard on
meson version within the build script:

if meson.version().version_compare('<=1.13')
tmp_install_depends = ...
else
tmp_install_depeends = installed_targets
endif

It might also be valuable to add a comment explaining the indirection
can be removed some time after we depend on 1.13 fully.

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