fix: don't panic when resolving / with roots (#310)

Author: sapphi-red

fixtures/misc/dir-with-index/index.js

@@ -355,7 +355,7 @@ impl<Fs: FileSystem> ResolverGeneric<Fs> {
                 return Ok(path);
             }
         }
-        if let Some(path) = self.load_roots(specifier, ctx) {
+        if let Some(path) = self.load_roots(cached_path, specifier, ctx) {
             return Ok(path);
         }
         // 2. If X begins with '/'
@@ -1086,15 +1086,28 @@ impl<Fs: FileSystem> ResolverGeneric<Fs> {
     /// defaults to context configuration option.
     ///
     /// On non-Windows systems these requests are resolved as an absolute path first.
-    fn load_roots(&self, specifier: &str, ctx: &mut Ctx) -> Option<CachedPath> {
+    fn load_roots(
+        &self,
+        cached_path: &CachedPath,
+        specifier: &str,
+        ctx: &mut Ctx,
+    ) -> Option<CachedPath> {
         if self.options.roots.is_empty() {
             return None;
         }
         if let Some(specifier) = specifier.strip_prefix(SLASH_START) {
-            for root in &self.options.roots {
-                let cached_path = self.cache.value(root);
-                if let Ok(path) = self.require_relative(&cached_path, specifier, ctx) {
-                    return Some(path);
+            if specifier.is_empty() {
+                if self.options.roots.iter().any(|root| root.as_path() == cached_path.path()) {
+                    if let Ok(path) = self.require_relative(cached_path, "./", ctx) {
+                        return Some(path);
+                    }
+                }
+            } else {
+                for root in &self.options.roots {
+                    let cached_path = self.cache.value(root);
+                    if let Ok(path) = self.require_relative(&cached_path, specifier, ctx) {
+                        return Some(path);
+                    }
                 }
             }
         }

src/lib.rs

@@ -90,3 +90,34 @@ fn roots_fall_through() {
         Ok(absolute_path)
     );
 }
+
+#[test]
+fn should_resolve_slash() {
+    let f = super::fixture();
+    let dir_with_index = super::fixture_root().join("./misc/dir-with-index");
+
+    #[rustfmt::skip]
+    let pass = [
+        ("should resolve if importer is root", vec![dir_with_index.clone()], &dir_with_index, dir_with_index.join("index.js")),
+    ];
+
+    for (comment, roots, directory, expected) in pass {
+        let resolver =
+            Resolver::new(ResolveOptions { roots: roots.clone(), ..ResolveOptions::default() });
+        let resolved_path = resolver.resolve(directory, "/").map(|r| r.full_path());
+        assert_eq!(resolved_path, Ok(expected), "{comment} {roots:?}");
+    }
+
+    #[rustfmt::skip]
+    let fail = [
+        ("should not resolve if not found", vec![f.clone()], &f),
+        ("should not resolve if importer is not root", vec![dir_with_index], &f)
+    ];
+
+    for (comment, roots, directory) in fail {
+        let resolver =
+            Resolver::new(ResolveOptions { roots: roots.clone(), ..ResolveOptions::default() });
+        let resolution = resolver.resolve(directory, "/");
+        assert_eq!(resolution, Err(ResolveError::NotFound("/".into())), "{comment} {roots:?}");
+    }
+}