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fix: omit stderr from metadata when generating hashes#330
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Occasionally I see `INFO: Checking for file changes...\n` in the metadata when generating hashes, which is extra useless info that causes bazel-diff to think the whole graph has changed. This silences the stderr so that it never gets added to the metadata. Fixes Tinder#329
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This was referenced Apr 27, 2026
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bazel-diff 17.0.1..18.0.5 configured BazelModService.getModuleGraphJson()
with stdout=CAPTURE, stderr=CAPTURE. In Process.kt, captureAll triggers
ProcessBuilder.redirectErrorStream(true), physically merging stderr into
stdout. The captured moduleGraphJson therefore contained bazel's INFO
lines ("INFO: Invocation ID: ...", "Loading: 0 packages loaded", etc.)
prepended to the actual JSON output.
PR Tinder#330 (shipped in v18.1.0) correctly switched stderr to SILENT but
broke format compatibility: any CI pipeline re-using a base graph from
17.0.1..18.0.5 and a head graph from 18.1.0+ hits parseModuleGraph's
try/catch on the polluted side, gets emptyMap(), and cascades into
findChangedModules reporting every head-side module as "added". The
downstream queryTargetsDependingOnModules then spawns thousands of
bazel query rdeps(...) subprocesses.
Make parseModuleGraph tolerant: attempt the whole-string parse first,
and on failure retry from the first '{' to end-of-string. On second
failure fall through to the existing emptyMap() behaviour. Clean input
continues to parse in one attempt with no extra allocation.
Tests:
- ModuleGraphParserTest: positive case for stderr-prefixed input.
- StderrPollutionRegressionTest: end-to-end regression guard covering
parse, findChangedModules, and the CalculateImpactedTargetsInteractor
dispatch path. Confirms the cross-version comparison now short-circuits
to computeSimpleImpactedTargets instead of the rdeps fan-out.
tinder-maxwellelliott
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May 13, 2026
) bazel-diff 17.0.1..18.0.5 configured BazelModService.getModuleGraphJson() with stdout=CAPTURE, stderr=CAPTURE. In Process.kt, captureAll triggers ProcessBuilder.redirectErrorStream(true), physically merging stderr into stdout. The captured moduleGraphJson therefore contained bazel's INFO lines ("INFO: Invocation ID: ...", "Loading: 0 packages loaded", etc.) prepended to the actual JSON output. PR #330 (shipped in v18.1.0) correctly switched stderr to SILENT but broke format compatibility: any CI pipeline re-using a base graph from 17.0.1..18.0.5 and a head graph from 18.1.0+ hits parseModuleGraph's try/catch on the polluted side, gets emptyMap(), and cascades into findChangedModules reporting every head-side module as "added". The downstream queryTargetsDependingOnModules then spawns thousands of bazel query rdeps(...) subprocesses. Make parseModuleGraph tolerant: attempt the whole-string parse first, and on failure retry from the first '{' to end-of-string. On second failure fall through to the existing emptyMap() behaviour. Clean input continues to parse in one attempt with no extra allocation. Tests: - ModuleGraphParserTest: positive case for stderr-prefixed input. - StderrPollutionRegressionTest: end-to-end regression guard covering parse, findChangedModules, and the CalculateImpactedTargetsInteractor dispatch path. Confirms the cross-version comparison now short-circuits to computeSimpleImpactedTargets instead of the rdeps fan-out.
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Occasionally I see
INFO: Checking for file changes...\nin the metadata when generating hashes, which is extra useless info that causes bazel-diff to think the whole graph has changed. This silences the stderr so that it never gets added to the metadata.I can't reproduce the issue exactly, but I've been running this patch internally for a little bit and it seems to be working.
Fixes #329