Add property tests for cycles, separators, interpolation (#322)

[leynos]

Summary

Closes #322

Adds the three groups of generative coverage the issue requests (proptest was already a dev-dependency, so no Cargo.toml change was needed):

1. Cycle detection (src/ir/cycle_analyse_tests.rs):

   • forward-edge-only graphs never report a cycle, regardless of node count or edge layout;
   • any graph with a back-edge (closed over a guaranteed chain) always reports one;
   • missing-dependency records are exactly the edges whose targets are absent from the target map (subset property plus completeness);
   • results are stable across arbitrary HashMap insertion orderings (prop_shuffle).

2. Ninja separator ordering (tests/ninja_property_tests.rs): for arbitrary non-empty inputs/implicit_deps/order_only_deps, the build line is exactly build out: act <inputs> | <implicit> || <order-only>; with empty implicit_deps the | separator is absent while || remains.

3. Command interpolation (src/ir/cmd_interpolate.rs): $in, $out, and both __NETSUKE_*_PLACEHOLDER__ tokens inside backticks survive verbatim for arbitrary path lists; placeholders outside backticks are always replaced with the joined lists.

Existing canonicalisation/detector property tests already covered determinism; these additions fill the gaps the issue identified.

Validation

• make check-fmt / make lint / make test — pass (38 suites; new ninja_property_tests binary included)

🤖 Generated with Claude Code

Summary by Sourcery

Add property-based tests to strengthen guarantees around cycle analysis, Ninja separator ordering, and command interpolation behavior.

Enhancements:

• Clarify and enforce invariants of the cycle analysis logic via property-based specifications for acyclic, cyclic, and missing-dependency scenarios.
• Document and lock in the expected Ninja build-line separator contract across varying dependency layouts using generative tests.
• Specify interpolation behavior for command templates with placeholders inside and outside backticks using property-based tests.

Tests:

• Introduce proptest-based coverage for cycle detection, missing-dependency reporting, and stability across HashMap insertion orders in the IR cycle analysis tests.
• Add property-based Ninja generator tests to assert correct ordering and conditional presence of | and || separators in build lines.
• Add property-based command interpolation tests to ensure placeholders inside backticks are preserved and placeholders outside are always substituted with joined path lists.

Chores:

• Add a regression corpus file for cycle analysis property tests.

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[sourcery-ai]

Reviewer's Guide

Adds property-based tests for cycle analysis, Ninja build-line separator ordering, and command interpolation, including helper generators and regression seeds, to strengthen invariants around cycles, missing dependencies, determinism across HashMap insertion order, Ninja output formatting, and placeholder handling within and outside backticks.

Flow diagram for command interpolation behavior with backticks and placeholders

flowchart LR
    Tmpl["template with tokens ($in, $out, __NETSUKE_INS_PLACEHOLDER__, __NETSUKE_OUTS_PLACEHOLDER__)"]
    Ins["ins: list of input paths"]
    Outs["outs: list of output paths"]

    Tmpl --> IC["interpolate_command(template, ins, outs)"]
    Ins --> IC
    Outs --> IC

    IC --> BQ{"token inside backticks?"}

    BQ -- "yes" --> Preserve["leave token text unchanged in output"]
    Preserve --> Cmd1["command equals original template"]

    BQ -- "no" --> PH{"is token a __NETSUKE_*_PLACEHOLDER__?"}

    PH -- "yes" --> Replace["replace placeholder with joined ins/outs (space separated)"]
    Replace --> Cmd2["command contains expanded paths and no PLACEHOLDER text"]

    PH -- "no" --> Other["process other tokens (e.g. $in, $out) according to existing rules"]

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File-Level Changes

Change	Details	Files
Introduce proptest-based coverage for cycle analysis invariants in the IR graph.	Add helper function to build DAGs from forward-only edge specifications using sequential node names and EdgeBuilder. Add property test asserting that graphs with only forward edges never produce cycle reports, regardless of node count or edge layout. Add property test asserting that graphs with a guaranteed back-edge over a connected chain always report a cycle. Add property test that missing-dependency records match exactly the edges whose targets are absent from the build target map, including subset and completeness properties. Add property test that analyse results (cycle and missing-dependencies) are stable across different HashMap insertion orders by shuffling node insertion.	src/ir/cycle_analyse_tests.rs proptest-regressions/ir/cycle_analyse_tests.txt
Add property-based tests to lock in Ninja build-line separator ordering for explicit, implicit, and order-only dependencies.	Introduce helper functions to construct small BuildGraph instances from string dependency lists and extract the generated Ninja build line. Define a string generator for short, shell-safe path names to use as inputs and dependencies. Add property test that for non-empty inputs/implicit/order-only lists, generated build lines always follow the `build out: act
Add command interpolation property tests ensuring correct handling of placeholders inside and outside backticks.	Add path_list strategy for generating short, shell-safe Utf8PathBuf lists and a token strategy for selecting placeholder tokens. Add property test asserting that $in, $out and placeholder tokens inside backticks are never substituted and survive verbatim after interpolation. Add property test asserting that placeholder tokens outside backticks are always replaced with joined input and output lists and that no placeholder substrings remain in the resulting command.	src/ir/cmd_interpolate.rs

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#322	Ensure proptest is available as a dev-dependency in the project (so property-based tests can be added).	✅
#322	Add proptest-based property tests for cycle detection covering: (a) forward-edge-only graphs never report cycles, (b) any graph with a back-edge reports a cycle, (c) missing-dependency records correspond exactly to edges whose targets are absent from the target map, and (d) results are stable across arbitrary HashMap insertion orderings.	✅
#322	Add proptest-based property tests for (a) Ninja separator ordering (inputs then `	implicit_depsthen

Possibly linked issues

• Add proptest property-based tests for cycle detection, Ninja separator ordering, and command interpolation #322: They match exactly: PR adds the cycle, separator, and interpolation proptest suites the issue specifies.

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