Incremental Checking

Problem Description

In watch mode, any file change triggers a full re-check of all files (full re-check), and the debounce uses busy-wait (checking every 50ms), causing the CPU to spin idle.

Solution

Use CheckSession to manage incremental checking state, leveraging ModuleDependencyGraph::affected_modules to only re-check affected files.

Implementation Flow

First check:
  Full check → Cache dependency graph + check results for each module

File change:
  1. affected_modules(changed_files) → Find affected modules
  2. Only re-parse and check affected modules
  3. Update cache and dependency graph

CheckSession

pub struct CheckSession {
    dep_graph: ModuleDependencyGraph,
    cache: ModuleCache,
    all_files: Vec<PathBuf>,
}

impl CheckSession {
    pub fn check_all(&mut self, files: &[PathBuf]) -> Result<CheckResult>;
    pub fn check_incremental(&mut self, changed_files: &[PathBuf]) -> Result<CheckResult>;
}

Known Limitations

• watch mode still uses busy-wait debounce (Instant::now() + recv_timeout in command.rs)
• check_incremental internally still calls check_files_with_diagnostics (full-check path), not truly utilizing incremental checking

Future Work

• A2/P1: Replace busy-wait debounce with HotReloader
• P2/P3: Integrate watch mode with CheckSession to achieve true incremental checking
• T9: Correctness tests for incremental checking