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

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).

cheers

andrew

--
Andrew Dunstan
EDB: https://www.enterprisedb.com