Rust: replace std::fs::canonicalize with dunce::canonicalize

Rust-analyzer turned out to be quite picky about paths, where
`//?/`-prefixed paths can lead to flaky failures. See

rust-lang/rust-analyzer#18894

for details.

This makes paths always be canonicalized with `dunce`. Previously,
`dunce` was used as a fallback, but that stopped working somewhere
after version 0.0.248 of rust-analyzer.

rust/extractor/src/main.rs

@@ -183,7 +183,10 @@ fn main() -> anyhow::Result<()> {
         .iter()
         .map(|file| {
             let file = std::path::absolute(file).unwrap_or(file.to_path_buf());
-            std::fs::canonicalize(&file).unwrap_or(file)
+            // On Windows, rust analyzer expects non-`//?/` prefixed paths (see [1]), which is what
+            // `std::fs::canonicalize` returns. So we use `dunce::canonicalize` instead.
+            // [1]: https://github.com/rust-lang/rust-analyzer/issues/18894#issuecomment-2580014730
+            dunce::canonicalize(&file).unwrap_or(file)
         })
         .collect();
     let manifests = rust_analyzer::find_project_manifests(&files)?;

rust/extractor/src/rust_analyzer.rs

@@ -17,7 +17,6 @@ use ra_ap_vfs::Vfs;
 use ra_ap_vfs::VfsPath;
 use ra_ap_vfs::{AbsPathBuf, FileId};
 use std::borrow::Cow;
-use std::iter;
 use std::path::{Path, PathBuf};
 use triomphe::Arc;
 
@@ -189,28 +188,10 @@ fn from_utf8_lossy(v: &[u8]) -> (Cow<'_, str>, Option<SyntaxError>) {
     (Cow::Owned(res), Some(error))
 }
 
-fn canonicalize_if_on_windows(path: &Path) -> Option<PathBuf> {
-    if cfg!(windows) {
-        dunce::canonicalize(path).ok()
-    } else {
-        None
-    }
-}
-
 pub(crate) fn path_to_file_id(path: &Path, vfs: &Vfs) -> Option<FileId> {
-    // There seems to be some flaky inconsistencies around paths on Windows, where sometimes paths
-    // are registered in `vfs` without the `//?/` long path prefix. Then it happens that paths with
-    // that prefix are not found. To work around that, on Windows after failing to find `path` as
-    // is, we then try to canonicalize it using dunce. Dunce will be able to losslessly convert a
-    // `//?/` path into its equivalent one in `vfs` without the prefix, if there is one.
-    iter::once(path.to_path_buf())
-        .chain(canonicalize_if_on_windows(path))
-        .filter_map(|p| {
-            Utf8PathBuf::from_path_buf(p)
-                .ok()
-                .and_then(|x| AbsPathBuf::try_from(x).ok())
-                .map(VfsPath::from)
-                .and_then(|x| vfs.file_id(&x))
-        })
-        .next()
+    Utf8PathBuf::from_path_buf(path.to_path_buf())
+        .ok()
+        .and_then(|x| AbsPathBuf::try_from(x).ok())
+        .map(VfsPath::from)
+        .and_then(|x| vfs.file_id(&x))
 }