patch: fix pch_context() for unified diffs with no leading context
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Authored by kevans on Aug 8 2025, 11:26 PM.

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des
pfg

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rGf97b6a8f84b3: patch: fix pch_context() for unified diffs with no leading context

Summary

When the first line of a file is a removal, we may not have any leading
context. Only adjusting p_context if context > 0 means that we
incorrectly believe that we have 100 lines of context when the reality
is that we have none.

This fixes a bug with fuzz-checking, which ends up fuzzing away the line
we're trying to replace if it's the first line in the file. We use
pch_context() to determine a reasonable max-fuzz.

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rG FreeBSD src repository

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Event Timeline

kevans created this revision.Aug 8 2025, 11:26 PM

Herald added a subscriber: imp. · View Herald TranscriptAug 8 2025, 11:26 PM

kevans requested review of this revision.Aug 8 2025, 11:26 PM

Harbormaster completed remote builds in B66127: Diff 160100.Aug 8 2025, 11:26 PM

pfg accepted this revision.Aug 8 2025, 11:34 PM

This revision is now accepted and ready to land.Aug 8 2025, 11:34 PM

Closed by commit rGf97b6a8f84b3: patch: fix pch_context() for unified diffs with no leading context (authored by kevans). · Explain WhyAug 29 2025, 7:25 PM

This revision was automatically updated to reflect the committed changes.

kevans added a commit: rGf97b6a8f84b3: patch: fix pch_context() for unified diffs with no leading context.

kevans added a reverting change: rGfb37e38fbe99: Revert "patch: fix pch_context() for unified diffs with no leading context".Aug 30 2025, 10:03 PM

FWIW, just about the best test one can make for a significant patch change is to have an exp-run over the ports tree.

In D51837#1194076, @pfg wrote:

FWIW, just about the best test one can make for a significant patch change is to have an exp-run over the ports tree.

Yeah, I noted in the thread the report came from that I'd exp-run it when I get back to this. My fear was having to fix a bunch of potentially dodgey patches because nobody really checks these things as long as patch(1) succeeds (based on past experience), but I bet the problem isn't actually as bad as I might think.