Optimized out unused states and production rules

[ehwan]

Optimizes the state machine for single-token-reduce-state:
delete and redirect all of the state that has only single reduce action, and that reduce rule has single token A -> a.

This could reduce runtime by 30%

[Copilot]

Pull Request Overview

This PR optimizes the state machine by identifying and eliminating single-token reduce states and unused production rules. The optimization removes states that only perform a single reduction of a single-token rule (A -> a), redirecting transitions to bypass these states.

• Added is_used field to production rules to track usage after optimization
• Implemented state machine optimization algorithm that bypasses single-token reduce states
• Updated parser state structures to support ShiftTarget with push/no-push semantics
• Modified reduce action signatures to return boolean indicating whether data was pushed

Reviewed Changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
rusty_lr_parser/src/pattern.rs	Adds is_used: true initialization to all newly created rules
rusty_lr_parser/src/nonterminal_info.rs	Adds is_used field to Rule struct for optimization tracking
rusty_lr_parser/src/grammar.rs	Implements main optimization algorithm and unused rule detection
rusty_lr_parser/src/emit.rs	Updates code generation to handle optimized states and unused rules
rusty_lr_core/src/parser/state.rs	Adds ShiftTarget struct and updates state interfaces
rusty_lr_core/src/parser/nondeterministic/context.rs	Updates shift operations to use ShiftTarget
rusty_lr_core/src/parser/deterministic/context.rs	Updates shift operations to use ShiftTarget
rusty_lr_core/src/parser/data_stack.rs	Changes reduce action return type to Result<bool, _>
rusty_lr_core/src/builder/state.rs	Updates state conversion to use ShiftTarget

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[Copilot]

[nitpick] The type annotation on line 1562-1564 is unnecessarily verbose and could be simplified using type inference, making the code more readable.

Suggested change

	let mut states: Vec<
	rusty_lr_core::parser::state::IntermediateState<usize, usize, usize, usize>,
	> = states.into_iter().map(Into::into).collect();
	let mut states = states.into_iter().map(Into::into).collect();

[Copilot]

The error message uses string interpolation syntax {rule_index} but should use {rule_index} within the unreachable! macro. This will not interpolate the variable correctly.

Suggested change

	reduce_action_case_streams.extend(quote! {
	#rule_index => unreachable!("{rule_index}: this production rule was optimized out"),
	#rule_index => unreachable!("{}: this production rule was optimized out", #rule_index),

[Copilot]

Same issue as above - the error message uses string interpolation syntax incorrectly within the unreachable! macro.

Suggested change

	reduce_action_case_streams.extend(quote! {
	#rule_index => unreachable!("{rule_index}: this production rule was optimized out"),
	#rule_index => unreachable!("{}: this production rule was optimized out", #rule_index),

[Copilot]

Same issue as above - the error message uses string interpolation syntax incorrectly within the unreachable! macro.

Suggested change

	reduce_action_case_streams.extend(quote! {
	#rule_index => unreachable!("{rule_index}: this production rule was optimized out"),
	#rule_index => unreachable!("{}: this production rule was optimized out", #rule_index),