perf: tell this package's frames apart without resolving paths

[jd]

_discover_versions_dir resolved every frame's filename to decide
whether it belonged to this package: a realpath walk, and so several
filesystem calls, per frame, per migration. In the Mergify engine that
was still about half of building a warm revision map for its ~350
migrations.

A frame of this package carries the filename the package was imported
by, so its directory is Path(__file__).parent; compare directories
against that (and its resolved form) and resolve nothing. 20,000
discovery calls from a migration file: 125 µs → 7.8 µs per call
(median of 7 runs), with the symlink cases of the previous commit still
covered by their tests.

🤖 Generated with Claude Code

Co-Authored-By: Claude Opus 5.5 (1M context) noreply@anthropic.com

[jd]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	fix: find the versions directory through symlinks	#55
2	perf: tell this package's frames apart without resolving paths	#56	👈

[mergify]

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Copilot review overview

🟡 Changes recommended

Relative symlink imports may fail package-frame detection until the absolute directory variant is included.

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Review effort: Lite
Findings: 1

Open (1)

• Handle relative symlink imports when matching package directories · New

What changed in this PR

Optimizes migration frame detection by avoiding per-frame path resolution while preserving symlink support.

Changes:

• Caches package directory variants.
• Compares caller directories without resolving paths.
• Retains symlink-aware migration discovery.

File	Summary	Finding
alembic_git_revisions/​_chain.py	Optimizes package-frame detection during stack walking.	Moderate issue: include the absolute imported-path directory to support relative symlink imports.

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[jd]

Revision history

#	Type	Changes	Reason	Date
1	initial	27facbe		2026-09-24 14:27 UTC
2	content	27facbe → c72d376	address review: make the imported package directory absolute, like the frames' directories it is compared with	2026-09-24 14:27 UTC

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-09-24 14:54 UTC · Rule: default · triggered by merge protections
• ✅ Checks skipped · PR is already up-to-date
• ✅ Merged — 2026-09-24 14:55 UTC · at 86b074212578160e3caa02bbbd0dfc825ebdc906 · squash

This pull request spent 19 seconds in the queue, including 1 second running CI.

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  • perf: tell this package's frames apart without resolving paths #56
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