new lint: unnecessary_path_exists by davidh167 · Pull Request #17331 · rust-lang/rust-clippy

davidh167 · 2026-07-01T07:23:55Z

Adds unnecessary_path_exists (nursery) which detects calls to Path::exists
used as an if condition immediately before a filesystem operation on the same
path, creating a TOCTOU race condition. The subsequent operation's return value
already indicates whether the path exists, making the exists() check redundant.

Detected patterns:

Direct: if path.exists() { path.metadata() }
With else branch: if path.exists() { ... } else { ... }
Compound condition: if path.exists() && other { ... }
Stored bool: let b = path.exists(); if b { ... }

Detected fs operations: metadata, symlink_metadata, canonicalize,
read_link, read_dir, is_file, is_dir, is_symlink.

changelog: new lint: [unnecessary_path_exists]

rustbot · 2026-07-01T07:24:01Z

Thanks for the pull request, and welcome! The Rust Project is excited to review your changes, and you should hear from @samueltardieu (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

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Why was this reviewer chosen?

The reviewer was selected based on:

Owners of files modified in this PR: 8 candidates
8 candidates expanded to 8 candidates
Random selection from Jarcho, dswij, llogiq, samueltardieu

samueltardieu

Please fix the PR title.

View changes since this review

samueltardieu · 2026-07-01T17:36:21Z

+            let ty = cx.typeck_results().expr_ty(recv).peel_refs();
+            if matches!(ty.opt_diag_name(cx), Some(sym::Path | sym::PathBuf)) {


You should rather check whether the method that is actually called is Path::exists, it would work with any type dereferencing to Path (including PathBuf).

samueltardieu · 2026-07-01T17:37:54Z

+        }
+
+        let stmts = block.stmts;
+        for (idx, stmt) in stmts.iter().enumerate() {


You could also zip block.stmts.iter() with block.smts.iter().skip(1).

samueltardieu · 2026-07-01T17:38:39Z

+) -> Option<Span> {
+    match expr.kind {
+        ExprKind::MethodCall(method_seg, recv, _, _) => {
+            if FS_METHODS.contains(&method_seg.ident.name.as_str()) {


Compare symbols, not strings.

samueltardieu · 2026-07-01T17:39:04Z

+        ExprKind::MethodCall(method_seg, recv, _, _) => {
+            if FS_METHODS.contains(&method_seg.ident.name.as_str()) {
+                let recv_ty = cx.typeck_results().expr_ty(recv).peel_refs();
+                if matches!(recv_ty.opt_diag_name(cx), Some(sym::Path | sym::PathBuf))


Same comment as above: check if this is a method belonging to Path.

samueltardieu · 2026-07-01T17:40:11Z

@@ -0,0 +1,169 @@
+#![warn(clippy::unnecessary_path_exists)]
+#![allow(unused)]


Suggested change

#![allow(unused)]

rustbot · 2026-07-01T17:40:51Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

davidh167 · 2026-07-02T00:18:19Z

Thanks for your valuable feedback! I've made the requested changes in the latest commit

davidh167 · 2026-07-02T00:20:40Z

@rustbot review

samueltardieu

Could you add tests involving macros, as well as tests involving a user-defined type implementing Deref<Target = Path>?

View changes since this review

samueltardieu · 2026-07-02T05:03:04Z

+    ///   if b { ... }`), only detects when the `if` immediately follows the `let`.
+    #[clippy::version = "1.98.0"]
+    pub UNNECESSARY_PATH_EXISTS,
+    nursery,


You need to choose a category, nursery is where lints go to die nowadays.

samueltardieu · 2026-07-02T05:04:53Z

+            return;
+        }
+
+        for (stmt, next_stmt) in block.stmts.iter().zip(block.stmts.iter().skip(1)) {


Rather than checking each and every block, it probably would be more efficient to first check for a call to the .exists() method and then analyze the surrounding block. This lint should probably be moved into the methods directory.

add unnecessary_path_exists lint to detect TOCTOU after Path::exists

da522a0

rustbot assigned samueltardieu Jul 1, 2026

rustbot added needs-fcp PRs that add, remove, or rename lints and need an FCP S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Jul 1, 2026

fix dogfood: use sym::exists and opt_diag_name

e090028

samueltardieu requested changes Jul 1, 2026

View reviewed changes

rustbot removed the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties label Jul 1, 2026

rustbot added the S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) label Jul 1, 2026

davidh167 changed the title ~~new lint: \unnecessary_path_exists``~~ new lint: unnecessary_path_exists Jul 1, 2026

address review: use type_dependent_def_id, symbol comparison, zip pairs

91865da

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties and removed S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) labels Jul 2, 2026

samueltardieu requested changes Jul 2, 2026

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rustbot added S-waiting-on-author Status: This is awaiting some action from the author. (Use `@rustbot ready` to update this status) and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties labels Jul 2, 2026

		let ty = cx.typeck_results().expr_ty(recv).peel_refs();
		if matches!(ty.opt_diag_name(cx), Some(sym::Path \| sym::PathBuf)) {

		@@ -0,0 +1,169 @@
		#![warn(clippy::unnecessary_path_exists)]
		#![allow(unused)]

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