feat(codegen): inline trivial pure parser rules before ATN construction - #352
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Add the opt-in, recognition-preserving `inline-trivial-rules` transform (`--inline-trivial-rules` / `--report-trivial-rules`, canonical order 150 between unreachable-rule pruning and precedence-ladder collapse). Two candidate classes are rewritten so the caller's decision sees the actual tokens instead of a rule transition, then the callee is removed: - token-set rules: a body that is only an alternation of single terminals is flattened into the referencing element as a token set, at any number of call sites; expansion is bounded by construction at one element per site. - single-use pure sequences: a single-alternative rule referenced exactly once moves into its call site as a parenthesized block. Candidates are inlined all-or-nothing and fail closed: configured or inferred entry rules, recursive, nullable, or target-code-observed rules, and bodies or call sites carrying labels, attributes, actions, predicates, options, arguments, or pinned precedence are declined with a recorded reason. Discovery re-runs after each accepted rewrite, so alias chains collapse in one invocation while every application removes exactly one rule, keeping the pass deterministic, idempotent, and free of composed growth. optimizations.json now records each candidate's rewritten call sites (`inlinedCallSites`) with original source spans beside status, reason, and removed rules. Motivated by the Atfinity grammar-optimization study, whose largest single win came from removing keyword-rule indirection. Because this generator builds the ATN natively after optional transforms, the flattened sets reach closure and prediction directly. Shared transform plumbing is extracted for reuse: TransformCloner and the rule/block tombstone helpers move to grammar/transform/clone.rs, and observed_rule_contexts/visit_elements move to transform/analysis.rs, with the precedence-ladder and prune passes rebased onto them. Verified: workspace tests (1500) and pedantic clippy are clean; the runtime testsuite passes 357/357 with zero skips both by default and with the pass forced on via ANTLR4_RUST_GEN_EXTRA_ARGS, where it applied in 5 descriptor grammars (including three ParserErrors recovery cases) with byte-identical upstream output and declined in 74; a CLI differential test compiles baseline and optimized parsers from one fixture and proves valid/invalid-input recognition parity alongside the intended generated-API changes. Refs #130
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📝 WalkthroughWalkthroughAdds an opt-in ChangesTrivial rule inlining
Estimated code review effort: 4 (Complex) | ~60 minutes Merge Risk: 🟡 Moderate · up to The opt-in parser optimization can inline token-set rules without preserving rule-level options such as case-insensitive matching, so affected grammars may recognize different input than before. This is a bounded but concrete correctness issue, and merge should wait until all rule-level semantics are covered or explicitly accepted; minor manifest consistency and reporting follow-ups also remain. Possibly related issues
Possibly related PRs
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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Inline comments:
In `@crates/antlr-rust-codegen/src/grammar/transform/artifact.rs`:
- Around line 64-65: Update the inlined_call_sites field in
TransformCandidateManifest to remove its empty-vector serialization skip, so
inlinedCallSites is always emitted as an array, including when empty. Preserve
the existing serialization behavior for the other fields.
In `@crates/antlr-rust-codegen/src/grammar/transform/passes/inline_trivial.rs`:
- Around line 296-331: Hoist the rule-level surface validation in eligibility so
it runs before the token_set early return, ensuring both InlineBody::TokenSet
and InlineBody::SingleUse candidates reject non-empty modifiers, arguments,
returns, locals, throws, options, case_insensitive, actions, catches, or
finally_action. Reuse the shared check from single_use_purity and leave
single_use_purity responsible only for its remaining candidate-specific
validations.
- Around line 336-375: The token_set_body function must deduplicate members
after flattening terminal and nested set alternatives, so repeated tokens appear
only once in the generated ElementKind::Set and applied_report counts unique
members. Preserve existing validation and ordering behavior while ensuring
duplicates are removed before returning the non-empty member list.
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crates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__alias_chain_shapes_and_candidates.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__configured_entry_declines.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__labeled_call_site_declines.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__nullable_and_recursive_declines.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__opaque_target_code_declines.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__single_use_inline_shapes_and_candidates.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__inline_trivial__tests__token_set_inline_shapes_and_candidates.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/src/grammar/transform/passes/snapshots/antlr_rust_codegen__grammar__transform__passes__precedence_ladder__tests__cel_ladder_collapse.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/tests/antlr4_rust_gen_cli/snapshots/antlr4_rust_gen_cli__cli__antlr4_rust_gen_help.snapis excluded by!**/*.snapcrates/antlr-rust-codegen/tests/antlr4_rust_gen_cli/snapshots/antlr4_rust_gen_cli__transforms__trivial_inline_optimization_manifest.snapis excluded by!**/*.snap
📒 Files selected for processing (16)
README.mdcrates/antlr-rust-codegen/src/builder.rscrates/antlr-rust-codegen/src/cli.rscrates/antlr-rust-codegen/src/config.rscrates/antlr-rust-codegen/src/grammar/transform/analysis.rscrates/antlr-rust-codegen/src/grammar/transform/artifact.rscrates/antlr-rust-codegen/src/grammar/transform/clone.rscrates/antlr-rust-codegen/src/grammar/transform/mod.rscrates/antlr-rust-codegen/src/grammar/transform/passes/inline_trivial.rscrates/antlr-rust-codegen/src/grammar/transform/passes/precedence_ladder.rscrates/antlr-rust-codegen/src/grammar/transform/passes/prune_unreachable.rscrates/antlr-rust-codegen/src/optimization/config.rscrates/antlr-rust-codegen/src/optimization/descriptor.rscrates/antlr-rust-codegen/src/testrig_cli.rscrates/antlr-rust-codegen/tests/antlr4_rust_gen_cli/transforms.rscrates/antlr-rust-codegen/tests/fixtures/antlr4-rust-gen/trivial-inline/Inline.g4
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📊 Source Code Metrics (this PR vs
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| File | Cognitive | ABC | MI | Hotspot | Churn |
|---|---|---|---|---|---|
| crates/antlr-rust-codegen/src/grammar/transform/passes/precedence_ladder.rs | 207 (main: 242) 🟢 | 795.07 (main: 894.72) 🟢 | 0 ⚪ | 1035 (main: 484) 🔴 | 1.30 (main: 1) 🔴 |
| crates/antlr-rust-codegen/src/grammar/transform/passes/inline_trivial.rs | 100 🆕 | 344.43 🆕 | 0 🆕 | 300 🆕 | 1.09 🆕 |
| crates/antlr-rust-codegen/src/builder.rs | 12 (main: 10) 🔴 | 64.58 (main: 61.63) 🔴 | 12.02 (main: 13.52) 🔴 | 72 (main: 50) 🔴 | 1.07 (main: 1.08) 🟢 |
| crates/antlr-rust-codegen/src/testrig_cli.rs | 34 ⚪ | 185.98 ⚪ | 2.32 (main: 2.37) 🔴 | 136 (main: 102) 🔴 | 1 ⚪ |
| crates/antlr-rust-codegen/src/optimization/config.rs | 36 (main: 33) 🔴 | 101.54 (main: 88.32) 🔴 | 10.70 (main: 13.34) 🔴 | 144 (main: 99) 🔴 | 1.01 (main: 1.01) 🔴 |
| crates/antlr-rust-codegen/src/grammar/transform/analysis.rs | 72 (main: 38) 🔴 | 136.31 (main: 87.66) 🔴 | 3.06 (main: 14.71) 🔴 | 288 (main: 76) 🔴 | 1 ⚪ |
| crates/antlr-rust-codegen/src/grammar/transform/artifact.rs | 2 ⚪ | 55.61 (main: 49.69) 🔴 | 12.74 (main: 14.05) 🔴 | 12 (main: 6) 🔴 | 2.73 (main: 2.82) 🟢 |
| crates/antlr-rust-codegen/src/grammar/transform/clone.rs | 15 🆕 | 65.10 🆕 | 21.26 🆕 | 15 🆕 | 1 🆕 |
| crates/antlr-rust-codegen/src/grammar/transform/passes/prune_unreachable.rs | 8 (main: 22) 🟢 | 19.87 (main: 33.75) 🟢 | 30.64 (main: 24.43) 🟢 | 24 (main: 44) 🟢 | 2 (main: 1) 🔴 |
| crates/antlr-rust-codegen/src/cli.rs | 13 ⚪ | 66.02 ⚪ | 16.64 (main: 17.12) 🔴 | 78 (main: 65) 🔴 | 2.82 (main: 2.90) 🟢 |
| crates/antlr-rust-codegen/src/grammar/transform/mod.rs | 0 ⚪ | 11.70 (main: 0) 🔴 | 23.26 (main: 27.49) 🔴 | 0 ⚪ | 1.01 (main: 1) 🔴 |
| crates/antlr-rust-codegen/src/config.rs | 0 ⚪ | 0 ⚪ | 40.91 (main: 41.91) 🔴 | 0 ⚪ | 1 ⚪ |
| crates/antlr-rust-codegen/src/optimization/descriptor.rs | 0 ⚪ | 0 ⚪ | 40.88 (main: 43.87) 🔴 | 0 ⚪ | 1 ⚪ |
Generated by mehen v1.9.0 — the code quality watcher.
Address review findings on the trivial-rule inlining pass: - share one rule_surface_is_observable check (now also covering caseInsensitive rule options) between both candidate classes, so a token-set rule carrying rule-level options, modifiers, throws, or exception clauses is declined instead of silently dropping that surface - deduplicate flattened token-set members so duplicate authored alternatives cannot overstate the manifest member count or emit redundant set entries - always emit inlinedCallSites in optimizations.json, matching the other candidate array fields instead of disappearing when empty - extract the shared single-unit transform fixture and the baseline/optimized/report CLI generation matrix into reusable test support, removing the duplication CPD flagged Re-verified: workspace tests and pedantic clippy clean; runtime testsuite 357/357 zero-skip with the pass forced on, still applying in 5 descriptor grammars with byte-identical upstream output.
Give removed-rule manifest entries an explicit optional target instead
of rendering the candidate's entry rule: precedence-ladder rungs keep
their surviving hub as the target, while inlined rules — which dissolve
into their call sites rather than into a single rule — serialize
targetRule as null, with the rewritten locations carried by
inlinedCallSites. This removes the degenerate self-referential
{"rule": "kw", "targetRule": "kw"} entries from trivial-rule inlining
candidates.
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Both findings addressed (your review examined 1. Token-set candidates bypass the rule-level purity gate — fixed in 373fc77 (CodeRabbit flagged the same gap). 2. Self-referential Re-verified after both commits: workspace tests and pedantic clippy clean; runtime testsuite 357/357 zero-skip with the pass forced on, still applying in 5 descriptor grammars with byte-identical upstream output. |
1 participant
Refs #130 (first slice: the two initial candidate classes, fail-closed eligibility, manifest auditability, and differential/testsuite validation; the multi-grammar A/B benchmark gating from the issue remains open).
What
Adds the opt-in, recognition-preserving
inline-trivial-rulesoptimization pass, running at canonical order 150 betweenprune-unreachable-rules(100) andcollapse-precedence-ladders(200). It inlines two classes of pure parser rules into their call sites before native ATN construction, so the caller's decision sees the actual tokens instead of a rule transition, and removes the inlined rule:New CLI flags
--inline-trivial-rulesand--report-trivial-rules(mutually exclusive; report mode emits onlyoptimizations.json), matching builder methods, and a README section between the prune and precedence-ladder sections.Fail-closed eligibility (all-or-nothing per candidate)
Declined with a recorded reason: configured or inferred entry rules; recursive (incl. mutual/indirect via SCC); nullable bodies; rules observed by grammar target code (opaque target code poisons everything, reusing the ladder pass's analysis); bodies with labels, attributes, actions, predicates, options, lexer commands, or exception clauses; call sites that bind a label, carry element options, pass arguments, or pin precedence.
EOF, wildcard, and inverted sets disqualify the token-set shape.Discovery re-runs after every accepted rewrite (alias chains like
a : b ; b : X | Y ;collapse in one invocation) and each application removes exactly one rule, so the fixpoint terminates, is deterministic (authored rule order), and is idempotent (second run is a no-op — tested).Auditability
Every candidate lands in
optimizations.jsonwith status (applied/eligible/declined), reason, safety class, before/after structural metrics, the removed rule, and — new manifest field —inlinedCallSites(caller, 1-based alternative, original source span). The field is skipped when empty, so existing precedence-ladder manifests are unchanged.Shared plumbing extracted
TransformClonerand the rule/block tombstone helpers moved from the precedence-ladder pass intogrammar/transform/clone.rs;observed_rule_contexts/visit_elementsmoved intotransform/analysis.rs. The ladder and prune passes are rebased onto them (behavioral no-op; only the ladder's Debug snapshot gained the new emptycall_sitesfield).Validation
trivial_rule_inlining_is_explicit_auditable_and_recognition_preserving)cargo test --workspace --all-features--helpsnapshot re-accepted for the two new flags)cargo clippy --locked --workspace --all-targets --all-features -- -D warningsANTLR4_RUST_GEN_EXTRA_ARGS="--inline-trivial-rules"--keep: applied in 5 descriptor grammars (incl. threeParserErrorsrecovery descriptors with byte-identical upstream output) and declined in 74Reviewer notes
SetElement.sourceIDs are duplicated across cloned sets at multiple call sites; that field is not a model node (validation doesn't walk it) and the ladder cloner already duplicates it verbatim.Summary by CodeRabbit
--inline-trivial-rulesto apply reviewed optimizations.--report-trivial-rulesfor dry-run analysis without modifying generated output.