perf: memoize import resolution

README.md

@@ -36,10 +36,10 @@ produced:
 
 | Fixture | Benchmarked files | Codescythe | Knip |
 | --- | ---: | ---: | ---: |
-| `microsoft/vscode` | 9,537 | 738.0ms | 5.76s |
-| `grafana/grafana` | 8,701 | 771.0ms | 9.29s |
-| `elastic/kibana` | 86,056 | 11.64s | 45.35s |
-| `renovatebot/renovate` | 2,488 | 118.5ms | 846.1ms |
+| `microsoft/vscode` | 9,398 | 1.11s | 4.22s |
+| `grafana/grafana` | 8,358 | 833.2ms | 9.51s |
+| `elastic/kibana` | 85,928 | 12.96s | 53.33s |
+| `renovatebot/renovate` | 2,456 | 154.5ms | 900.5ms |
 
 Counts reflect each fixture's generated benchmark config after excludes. Run
 `pnpm benchmark` to measure the same fixtures locally.

benchmarks/README.md

@@ -63,7 +63,7 @@ unset.
 
 ## Current Numbers
 
-Local run on May 20, 2026 with the checked-in fixture configs:
+Local run on May 22, 2026 with the checked-in fixture configs:
 
 ```sh
 bazel build -c opt //crates/codescythe_cli:codescythe
@@ -73,14 +73,14 @@ node --experimental-transform-types benchmarks/run.ts --samples 3 --warmups 1 --
 ```text
 fixture    tool        mean       rme        samples  ops/sec
 ---------  ----------  ---------  ---------  -------  -------
-vscode     codescythe  1468.2ms   +/-4.42%   4        0.68
-vscode     knip        4669.8ms   +/-27.79%  3        0.21
-grafana    codescythe  1031.1ms   +/-3.69%   5        0.97
-grafana    knip        10302.1ms  +/-28.43%  3        0.10
-kibana     codescythe  15932.2ms  +/-10.85%  3        0.06
-kibana     knip        61479.6ms  +/-14.43%  3        0.02
-renovate   codescythe  176.3ms    +/-2.92%   17       5.67
-renovate   knip        954.5ms    +/-18.01%  5        1.05
+vscode     codescythe  1111.9ms   +/-1.36%   5        0.90
+vscode     knip        4223.1ms   +/-4.89%   3        0.24
+grafana    codescythe  833.2ms    +/-4.11%   5        1.20
+grafana    knip        9513.4ms   +/-56.75%  3        0.11
+kibana     codescythe  12963.8ms  +/-25.85%  3        0.08
+kibana     knip        53327.5ms  +/-33.69%  3        0.02
+renovate   codescythe  154.5ms    +/-4.79%   18       6.47
+renovate   knip        900.5ms    +/-6.09%   5        1.11
 ```
 
 ## Vendored Conformance

crates/codescythe/analyze/resolver.rs

@@ -1,8 +1,11 @@
 use super::*;
 
+use std::cell::RefCell;
+
 pub(super) struct ModuleResolver {
     resolver: ResolverGeneric<IgnoredResolverMetadataFileSystem>,
     index_by_path: HashMap<PathBuf, usize>,
+    resolution_cache: RefCell<HashMap<(String, String), ImportResolution>>,
 }
 
 struct IgnoredResolverMetadataFileSystem {
@@ -94,6 +97,7 @@ impl FileSystem for IgnoredResolverMetadataFileSystem {
     }
 }
 
+#[derive(Clone, Copy)]
 pub(super) enum ImportResolution {
     Project(usize),
     External,
@@ -149,10 +153,24 @@ impl ModuleResolver {
         Ok(Self {
             resolver,
             index_by_path,
+            resolution_cache: RefCell::new(HashMap::new()),
         })
     }
 
     pub(super) fn resolve(&self, from: &FileData, specifier: &str) -> Result<ImportResolution> {
+        let cache_key = (from.relative.clone(), specifier.to_string());
+        if let Some(resolution) = self.resolution_cache.borrow().get(&cache_key) {
+            return Ok(*resolution);
+        }
+
+        let resolution = self.resolve_uncached(from, specifier)?;
+        self.resolution_cache
+            .borrow_mut()
+            .insert(cache_key, resolution);
+        Ok(resolution)
+    }
+
+    fn resolve_uncached(&self, from: &FileData, specifier: &str) -> Result<ImportResolution> {
         match self.resolver.resolve_file(&from.path, specifier) {
             Ok(resolution) => {
                 let path = normalize_path(resolution.path());