fix(npm): improve declaration resolution for filename with different extensions (#19966)

postcss was importing `./index.js` from `./index.d.mts` where there also
existed a `./index.d.ts`.

Closes #19575

1 files changed, 44 insertions, 14 deletions

diff --git a/ext/node/resolution.rs b/ext/node/resolution.rs
index ce02f31f2..bb25124bf 100644
--- a/ext/node/resolution.rs
+++ b/ext/node/resolution.rs
@@ -527,37 +527,67 @@ impl NodeResolver {
     fn probe_extensions(
       fs: &dyn deno_fs::FileSystem,
       path: &Path,
+      lowercase_path: &str,
       referrer_kind: NodeModuleKind,
     ) -> Option<PathBuf> {
-      let specific_dts_path = match referrer_kind {
-        NodeModuleKind::Cjs => with_known_extension(path, "d.cts"),
-        NodeModuleKind::Esm => with_known_extension(path, "d.mts"),
-      };
-      if fs.exists(&specific_dts_path) {
-        return Some(specific_dts_path);
+      let mut searched_for_d_mts = false;
+      let mut searched_for_d_cts = false;
+      if lowercase_path.ends_with(".mjs") {
+        let d_mts_path = with_known_extension(path, "d.mts");
+        if fs.exists(&d_mts_path) {
+          return Some(d_mts_path);
+        }
+        searched_for_d_mts = true;
+      } else if lowercase_path.ends_with(".cjs") {
+        let d_cts_path = with_known_extension(path, "d.cts");
+        if fs.exists(&d_cts_path) {
+          return Some(d_cts_path);
+        }
+        searched_for_d_cts = true;
       }
+
       let dts_path = with_known_extension(path, "d.ts");
       if fs.exists(&dts_path) {
-        Some(dts_path)
-      } else {
-        None
+        return Some(dts_path);
+      }
+
+      let specific_dts_path = match referrer_kind {
+        NodeModuleKind::Cjs if !searched_for_d_cts => {
+          Some(with_known_extension(path, "d.cts"))
+        }
+        NodeModuleKind::Esm if !searched_for_d_mts => {
+          Some(with_known_extension(path, "d.mts"))
+        }
+        _ => None, // already searched above
+      };
+      if let Some(specific_dts_path) = specific_dts_path {
+        if fs.exists(&specific_dts_path) {
+          return Some(specific_dts_path);
+        }
       }
+      None
     }
 
     let lowercase_path = path.to_string_lossy().to_lowercase();
     if lowercase_path.ends_with(".d.ts")
       || lowercase_path.ends_with(".d.cts")
-      || lowercase_path.ends_with(".d.ts")
+      || lowercase_path.ends_with(".d.mts")
     {
       return Some(path);
     }
-    if let Some(path) = probe_extensions(&*self.fs, &path, referrer_kind) {
+    if let Some(path) =
+      probe_extensions(&*self.fs, &path, &lowercase_path, referrer_kind)
+    {
       return Some(path);
     }
     if self.fs.is_dir(&path) {
-      if let Some(path) =
-        probe_extensions(&*self.fs, &path.join("index"), referrer_kind)
-      {
+      let index_path = path.join("index.js");
+      if let Some(path) = probe_extensions(
+        &*self.fs,
+        &index_path,
+        &index_path.to_string_lossy().to_lowercase(),
+        referrer_kind,
+      ) {
         return Some(path);
       }
     }