Incremental Check

Problem Statement

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

Solution

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

Implementation Flow

First check:
  Full check → Cache dependency graph + check result 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 debouncing (Instant::now() + recv_timeout in command.rs)
• check_incremental internally still calls check_files_with_diagnostics (full path), not truly leveraging incremental checking

Future Work

• A2/P1: Replace busy-wait debouncing with HotReloader
• P2/P3: Integrate watch mode with CheckSession for true incremental checking
• T9: Incremental check correctness tests