Add custom predicate extensions via [[predicate]]#238
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nikomatsakis
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Jun 9, 2026
Plugin authors can now define custom predicate functions that extend the predicate language. When a crates expression uses an unknown function name (e.g., `battery-pack(cli>=0.3)`), Symposium looks it up in the custom predicate registry and spawns the declared command with the raw argument appended. Key additions: - Predicate::Custom variant with balanced-paren parsing - [[predicate]] section in plugin TOML manifests - CustomPredicateEvaluator with per-sync caching - Witness support (stdout JSON with selectedCrates) - Runnable::spawn helper on symposium-install - Full sync integration (predicates resolved before evaluation) - Integration tests and reference documentation Co-authored-by: Claude <claude@anthropic.com>
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Move the CustomPredicateEvaluator's entries and cache directly into PredicateContext, making evaluate()/witness() take &mut self. This eliminates the separate _with_evaluator function variants and fixes a bug where group-level custom predicates were silently evaluated as false (because load_skills_for_group called evaluate() without the external evaluator). Co-authored-by: Claude <claude@anthropic.com>
- Extract `validate_custom_predicate_name` as a single public helper in predicate.rs, enforcing `[a-zA-Z][a-zA-Z0-9_]*` + no builtin collision. Used by both the expression parser and plugin manifest validation. - Fix CrateList::parse to use split_top_level (paren-aware comma split) so custom predicates like `bp(a, b)` in SKILL.md frontmatter are not incorrectly split on the inner comma. - Add collision tests for build_custom_predicate_registry (two-way and three-way). Co-authored-by: Claude <claude@anthropic.com>
The `crates` field should only accept crate-name atoms (e.g. `serde`, `serde>=1.0`, `*`). Full predicate expressions including custom predicates belong in the `predicates` field. This matches the design decision from the Zulip discussion: the fields serve distinct roles and should not accept each other's syntax. - AtomParser now errors on `(` instead of parsing function calls - Remove dead `consume_balanced_parens` from AtomParser - Fix test fixture to use `predicates` instead of `crates` - Update CrateList tests to assert rejection Co-authored-by: Claude <claude@anthropic.com>
Assert that the `crates` field rejects all function-call forms (all(), crate(), not(), shell()) and that the `predicates` field rejects bare crate-atom syntax (serde, tokio>=1.0, *). Co-authored-by: Claude <claude@anthropic.com>
The custom predicate tests used Runnable::Exec with hardcoded /bin/true and /bin/false paths which may not exist on all CI environments. Replace with Runnable::Script using tempfile shell scripts that explicitly `exit 0` or `exit 1`. Co-authored-by: Claude <claude@anthropic.com>
nikomatsakis
commented
Jun 9, 2026
…ource
Address PR review feedback:
- Add comment to fixture explaining the script is test-generated
- Add test that verifies the predicate argument ("cli") is passed correctly
- Add test showing wrong argument causes predicate failure
- Add witness integration test: custom predicate returns selectedCrates
JSON, which drives `source = "crate"` skill resolution from a path dep
Co-authored-by: Claude <claude@anthropic.com>
nikomatsakis
commented
Jun 9, 2026
Previously, invalid JSON on stdout was silently ignored (predicate still passed with no witness). Now non-empty invalid stdout causes the predicate to evaluate as false, since the command likely has a bug. Empty stdout remains valid (pass with no witness crates). Co-authored-by: Claude <claude@anthropic.com>
Any invalid entry in selectedCrates (e.g. bad semver) now fails the whole predicate rather than silently skipping it. Consistent with the principle that non-empty invalid stdout means the command has a bug. Co-authored-by: Claude <claude@anthropic.com>
nikomatsakis
commented
Jun 9, 2026
- `foo()` and `foo( )` do not append any argument to the command - Leading/trailing whitespace is stripped from the argument - Add unit tests verifying parsing and runtime behavior Co-authored-by: Claude <claude@anthropic.com>
…ource - Add cross-plugin predicate tests: one plugin defines [[predicate]], another plugin uses it in predicates = [...]. Demonstrates that custom predicates are always registered regardless of which plugin defines them and can be used by any other plugin. - Tests both pass and fail paths for cross-plugin usage. Co-authored-by: Claude <claude@anthropic.com>
Replace the raw HashMap<String, ResolvedCustomPredicate> with a dedicated CustomPredicateRegistry struct that exposes only the operations we need (get, iter, contains_key, len, is_empty). Co-authored-by: Claude <claude@anthropic.com>
Co-authored-by: Claude <claude@anthropic.com>
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What does this PR do?
Plugin authors can now define custom predicate functions that extend the predicate language. When a crates expression uses an unknown function name (e.g.,
battery-pack(cli>=0.3)), Symposium looks it up in the custom predicate registry and spawns the declared command with the raw argument appended.Key additions:
Disclosure questions
AI disclosure.
Questions for reviewers.