perf: reuse owned parent realpath buffer in realpath_uncached (#278)

Author: stormslowly

src/cache.rs

@@ -9,7 +9,7 @@ use std::{
   sync::Arc,
 };
 
-use camino::{Utf8Path, Utf8PathBuf};
+use camino::{Utf8Component, Utf8Path, Utf8PathBuf};
 use dashmap::{DashMap, DashSet};
 use futures::future::BoxFuture;
 use rustc_hash::FxHasher;
@@ -18,7 +18,6 @@ use tokio::sync::OnceCell as OnceLock;
 use crate::{
   context::ResolveContext as Ctx,
   package_json::{off_to_location, PackageJson},
-  path::PathUtil,
   resolver_path::{hash_path, ResolverPath},
   FileMetadata, FileSystem, JSONError, ResolveError, ResolveOptions, TsConfig,
 };
@@ -272,10 +271,18 @@ impl CachedPathImpl {
               .map(|path| Some(Utf8PathBuf::from_path_buf(path).expect("path should be UTF-8")));
           }
           if let Some(parent) = self.parent() {
-            let parent_path = parent.realpath(fs).await?;
-            return Ok(Some(
-              parent_path.normalize_with(self.path.strip_prefix(parent.path()).unwrap()),
-            ));
+            let mut real_path = parent.realpath(fs).await?;
+            // Unnormalized paths (e.g. from alias values or absolute specifiers) can
+            // end in `..`, where `file_name()` returns `None` and would silently drop
+            // the component; POSIX semantics pop it after the parent is resolved.
+            match self.path.components().next_back() {
+              Some(Utf8Component::Normal(segment)) => real_path.push(segment),
+              Some(Utf8Component::ParentDir) => {
+                real_path.pop();
+              }
+              _ => {}
+            }
+            return Ok(Some(real_path));
           }
           Ok(None)
         })

src/tests/symlink.rs

@@ -157,3 +157,27 @@ async fn test() -> io::Result<()> {
 
   Ok(())
 }
+
+// With `symlinks` enabled, realpath must apply `..` components after resolving
+// the parent, not drop them. Unnormalized paths reach the resolver from user
+// input: absolute specifiers (kept verbatim on non-Windows), exact-match alias
+// values, and the `directory` argument of `resolve`.
+#[tokio::test]
+async fn dotdot_in_unnormalized_input() {
+  let root = super::fixture_root().join("enhanced_resolve");
+  let expected = Ok(root.join("lib/index.js"));
+  let resolver = Resolver::default();
+
+  let specifier = root.join("test/../lib/index.js");
+  let resolution = resolver
+    .resolve(root.join("test"), specifier.to_str().unwrap())
+    .await
+    .map(|r| r.full_path());
+  assert_eq!(resolution, expected, "absolute specifier containing `..`");
+
+  let resolution = resolver
+    .resolve(root.join("test/.."), "./lib/index.js")
+    .await
+    .map(|r| r.full_path());
+  assert_eq!(resolution, expected, "directory ending in `..`");
+}