Initial code import - #1
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macOS runners use a much longer $TMPDIR than Linux, so the repo root path pushed the error message past Format's line margin before it got sanitized to $CENTRAL_ROOT in expect tests, causing the message to wrap unpredictably (splitting even "Repo" from the quoted path). Wrap the path-bearing sentence in an hbox so it's never auto-wrapped, move "commit or stash them first" into a dedicated hint.
The earlier hbox fix wasn't enough: on macOS CI, the real repo_root path (under a much longer $TMPDIR than Linux) can be wide enough that the whole atomic hbox no longer fits on the line, so Format still breaks - just before "Repo" instead of mid-sentence. No box discipline can make an oversized real path fit. Instead, teach the CLI to print a short, fixed placeholder for repo_root when a CENTRAL_TEST_REPO_ROOT env var is set, and have the test harness set it (to the same "$CENTRAL_ROOT" placeholder it already substitutes post hoc) around the central subprocess it spawns. This keeps the formatted message short and platform-independent before Format ever makes a wrapping decision, so the hbox is no longer needed.
Central_test_harness.redact rewrites every registered revision it finds
in a piece of text by folding replace_all over the progressively
rewritten accumulator, once per registered pattern (full shas and every
abbreviated prefix, longest first). A mock rev is just a 40-hex-char
digest, indistinguishable from a real one, so it can itself contain a
short run that coincidentally matches some other, unrelated commit's
abbreviated real-sha prefix registered later - corrupting an
already-correct mock rev in place once that later pattern is applied.
This is what produced a flaky CI failure: a conflict marker's trailing
revision came out as ">>>>>>> 11855121185612b25613f2e5b473e5231185512b"
instead of the correct
">>>>>>> 1185512b92d612b25613f2e5b473e5231185512b".
Add a deterministic, git-independent regression test that reproduces the
same collision directly against redact/register_rev, as a new page in
the mdexp book, "Deterministic Revisions": it narrates why the test
harness redacts revisions at all (so snapshots stay stable across runs)
and then the substitution-order edge case this test pins down. Wired
into SUMMARY.md and cross-linked from the mock rev already visible in
the Import chapter's conflict example.
This currently fails (red):
-| [%expect {| 1185512b92d612b25613f2e5b473e5231185512b |}]
+| [%expect {| 1185512f452612b25613f2e5b473e5231185512b |}]
confirming the test actually exercises the bug before the next commit
fixes it.
redact rewrote the text once per registered pattern (full shas and every
abbreviated prefix), folding each replace_all pass over the progressively
rewritten accumulator - so a later, shorter pattern could match and
corrupt a mock rev an earlier pass had already substituted in, whenever
that mock rev's hex text coincidentally contained the later pattern.
Fix: scan the original text once, left to right, trying all patterns
(longest first) at each position, instead of re-scanning growing
substituted output once per pattern. Same asymptotic cost, but
already-written output is never re-matched.
Turns the regression test added in the previous commit green:
-| [%expect {| 1185512f452612b25613f2e5b473e5231185512b |}]
+| [%expect {| 1185512b92d612b25613f2e5b473e5231185512b |}]
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Initiate the project, go through CI fixes.