fix: read compose the way compose does in the contract gate

[goldyfruit]

🤖 Auto-generated by Claude Opus 5 (1M context) via Claude Code — NOT human-reviewed. Verify before acting.

The contract gate reads the compose files with a regex over the raw text, and that disagrees with compose in four ways. An empty or comment-only docker-compose*.yml parses to None, so the scan raises AttributeError and the gate dies with a traceback instead of a contract message. The variable pattern accepts only upper-case names, so a lower-case one is silently not an input. It matches the name inside $$NAME, which is compose's escape for a literal dollar and never interpolates. And because it runs over raw text it reads YAML keys and comments, neither of which compose substitutes into.

A fifth gap is on the other side of the same question: a service that writes environment: - NAME, with no value, takes that variable from the host environment. It is a value the consumer has to supply, and no $NAME appears anywhere for the scan to find, so the contract simply omitted it.

None of these fire on the compose files as they stand, which is the point: every one of them produces a contract that looks right and is wrong, and the drift this gate exists to catch is exactly the kind nothing else notices. The scan now walks the parsed document's values rather than the raw text, accepts the names compose accepts, discards escaped dollars, and records pass-through environment entries as required inputs. An empty document reads as no services.

scripts/test_contract.py holds one fixture per case, run from the contract job. Six of the seven fail against the previous scan — five wrong answers and the AttributeError. The derived contract for the compose files in this repository is byte-identical before and after, so contract.yml is unchanged and the gate still passes.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Improved environment variable detection in contract validation, including lowercase and underscore-prefixed names.
  • Correctly handles escaped dollar signs, defaults, required variables, and pass-through environment entries.
  • Ignores dollar signs in YAML keys and comments.
  • Supports empty or comment-only compose files without errors.

• Tests

  • Added automated coverage for contract parsing and environment variable scenarios.

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📒 Files selected for processing (2)

• scripts/contract.py
• scripts/test_contract.py

📝 Walkthrough

Walkthrough

The contract parser now scans parsed Compose values, supports additional variable forms, identifies pass-through environment variables, handles empty files, and runs focused tests in the pull-request workflow.

Changes

Compose contract derivation

Layer / File(s)	Summary
Variable scanning and normalization scripts/contract.py	Variable matching now handles escaped dollars, lower-case names, underscore-leading names, and lower-case tag variable names. Scanning uses string values from the parsed YAML document.
Contract derivation inputs scripts/contract.py	Empty Compose documents produce no services. Valueless environment entries become required inputs for both list and mapping forms.
Contract validation in CI scripts/test_contract.py, .github/workflows/pull-request.yml	The new unittest suite covers interpolation, defaults, escaped dollars, YAML keys, pass-through variables, and empty files. The pull-request workflow runs the suite after contract validation.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Bug fix

Merge Risk: 🟡 Moderate · up to ff653

Compose configurations using alternative variable expressions can be rejected by the contract gate despite allowing the variable to be unset. Fix this before merge.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: updating the contract gate to read Compose files according to Compose interpolation behavior.
Docstring Coverage	✅ Passed	Docstring coverage is 91.67% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 12 functions across 2 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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Actionable comments posted: 1

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Inline comments:
In `@scripts/contract.py`:
- Line 53: The VAR regex used by derive() must recognize Compose alternative
operators + and :+ as optional references, so ${VAR+replacement} and
${VAR:+replacement} do not mark VAR as required. Update the operator matching
while preserving existing variable forms, and add regression tests covering both
alternatives.

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⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Advanced

Run ID: 7758912e-111d-4e70-9909-6fd5eb7423e9

📥 Commits

Reviewing files that changed from the base of the PR and between 64976c5 and ff6531a.

📒 Files selected for processing (3)

• .github/workflows/pull-request.yml
• scripts/contract.py
• scripts/test_contract.py

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[goldyfruit]

Fixed, and the regex is gone rather than extended.

Both operator families are handled now. ${VAR+value} and ${VAR:+value} resolve to an empty string when VAR is unset, so the compose stands on its own and the variable is no longer reported as required; ? and :? still are, because they state no default and fail.

The nested case needed more than another alternation. ${PRIMARY:-${FALLBACK}} cannot be read by any pattern that ends the expression at the first }, because that lands inside the default and FALLBACK is never seen. So compose_variables() matches braces by depth and then scans the text after the operator in turn, since a default or replacement is a value like any other: ${A:-${B:-${C}}} yields A and B optional and C required.

I checked the semantics against compose 5.5.0 rather than inferring them, and it agrees on every case, including warning that FALLBACK is not set — which is the evidence it belongs in the contract.

The single-quoted case is a different matter and I have not changed it, because compose does not behave that way. Quote style is a YAML construct; compose interpolates the resulting value either way. The same compose run:

environment:
  SINGLE: '$HOME'
  DOUBLE: "$HOME"

SINGLE: /home/gtrellu
DOUBLE: /home/gtrellu

Skipping single-quoted scalars would drop a variable compose really does substitute, and the contract would then under-report its required inputs — the failure this gate exists to prevent. I have added test_a_single_quoted_value_is_still_interpolated to hold that behaviour in place; it passes both before and after this change, which is the point.

Regression tests cover the alternative operators and the nested default, and both fail against the previous regex. The gate itself still derives the same contract with no drift.

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