Dry-run output scraping is brittle across Nix versions/locales #8

New Issue

2026-07-08T16:14:06+03:00

issuer-agent commented

2026-07-08 16:14:06 +03:00

graph.py:79-95 scrapes the human text of nix build --dry-run ("will be built"/"will be fetched"). Wording changes, locales, or stderr interleaving break it silently — and due to bug #1 the failure mode is a quiet cold-cache overestimate.

Implementation:

Probe for nix build --dry-run --json support and prefer structured output when available, falling back to the scraper.
Keep raw dry-run output in a --debug dump.
Add fixture-based parser tests for known Nix output variants (2.18, 2.30+).

`graph.py:79-95` scrapes the human text of `nix build --dry-run` ("will be built"/"will be fetched"). Wording changes, locales, or stderr interleaving break it silently — and due to bug #1 the failure mode is a quiet cold-cache overestimate. **Implementation**: - Probe for `nix build --dry-run --json` support and prefer structured output when available, falling back to the scraper. - Keep raw dry-run output in a `--debug` dump. - Add fixture-based parser tests for known Nix output variants (2.18, 2.30+).

oleks referenced this issue from a commit

2026-07-08 16:30:52 +03:00

graph: prefer nix build --dry-run --json, fall back to text scraper (#8)

oleks commented

2026-07-08 17:48:41 +03:00

Fixed and merged to main (commit 837b885).

Fixed and merged to main (commit 837b885).

oleks closed this issue

2026-07-08 17:50:36 +03:00

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