fix(path): clarify error message when path dependency has wrong package by raushan728 · Pull Request #16927 · rust-lang/cargo

raushan728 · 2026-04-22T10:39:39Z

When a path dependency specifies a package name that doesn't match what's
found at that path, Cargo now shows helpful hints about what packages exist
nearby instead of the confusing "location searched" message.

…rust-lang#15296)

rustbot · 2026-04-22T10:39:44Z

r? @epage

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epage

Thanks!

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epage · 2026-04-22T11:47:46Z

    pub fn load(&self) -> CargoResult<()> {
        let mut package = self.package.borrow_mut();
        if package.is_none() {
+            if !self.path.join("Cargo.toml").exists() {


Why was this added?

It was an earlier attempt to handle missing Cargo.toml - reverted because it was too broad and broke existing tests. Now i use typed error detection in registry.rs

From #16927 (comment)

Note for reviewers: The change in registry.rs is needed to handle case 2 and case 3 (where bar/ exists as a directory but has no Cargo.toml). Without it the IO error fires before the resolver reaches activation_error_path_hints. The suppression is guarded by three conditions: path source, typed ManifestError with NotFound, and has_nearby_manifests confirming subdirectory packages exist.

epage · 2026-04-22T11:51:33Z

+                            if s.is_empty() {
+                                s.push('.');
+                            }
+                            if !s.ends_with('/') {


Why are we doing this?

use file_name() to show the actual directory name (e.g. foo/) instead of ./ when the path equals the parent root

That isn't a complete sentence, making it harder to follow what you mean. I don't see how a file_name() (which?) even fits into this.

When path == parent_root, strip_prefix returns an empty string. In that case we fall back to path.file_name() to show the directory name (e.g. foo/) rather than an empty or confusing path

file_name() doesn't make sense here. We should probably be using pathdiff or using an absolute path

The original point I raised was actually about always appending / since that isn't something users are likely to do

raushan728 · 2026-04-23T12:43:07Z

Note for reviewers: The change in registry.rs is needed to handle
case 2 and case 3 (where bar/ exists as a directory but has no
Cargo.toml). Without it the IO error fires before the resolver
reaches activation_error_path_hints. The suppression is guarded by
three conditions: path source, typed ManifestError with NotFound,
and has_nearby_manifests confirming subdirectory packages exist.

epage · 2026-04-23T14:22:27Z

+            let res = source.query(dep, kind, f).await;
+            if let Err(e) = &res {
+                if dep.source_id().is_path()
+                    && crate::core::resolver::errors::is_manifest_not_found(e)
+                    && has_nearby_manifests(dep)
+                {
+                    return Ok(());
+                }
+            }
+            res.with_context(|| format!("unable to update {}", source.source_id()))


This has really ballooned in complexity, including the idea of "catching" specific errors.

View changes since the review

The registry.rs change was needed because without it, the IO error fires before the resolver reaches the diagnostic code for cases 2/3.

Is there a cleaner way you'd suggest to intercept this early failure so we can still provide helpful hints for those cases? Happy to rework the approach if you have a better path in mind.

From #16927 (comment)

Regarding registry.rs - every alternative approach I tried but they broke existing tests. This is the cleanest I could find while keeping everything green.

I have strong reservations about this approach and would need to understand why there is no other way, rather than being told that.

…ge (rust-lang#15296) When a path dependency points to a directory with a different package, show which package exists there and where the correct one can be found.

epage · 2026-04-27T15:26:07Z

+        let _ = writeln!(
+            &mut msg,
+            "no matching package named `{}` found at `{}`",
+            dep.package_name(),
+            rel_path(&path),
+        );
+        let _ = write!(
+            &mut msg,
+            "required by {}",
+            describe_path_in_context(resolver_ctx, &parent.package_id()),
+        );


Why does is_handled_custom_path_error till exist?

On the surface, it looks like we use it to move the location searched: message into the line before it but it isn't clear why we feel that complexity is worth it.

View changes since the review

epage · 2026-04-27T15:27:04Z

+/// Checks if an error is a "manifest not found" error (Cargo.toml missing).
+/// This is used to allow the resolver to continue and provide helpful hints
+/// for path dependencies instead of failing immediately with a load error.
+pub fn is_manifest_not_found(err: &anyhow::Error) -> bool {


If we keep this, why is it here when only used in the Source?

View changes since the review

test(path): add tests for path dependency wrong package error message (…

2f317eb

…rust-lang#15296)

rustbot added A-dependency-resolution Area: dependency resolution and the resolver S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 22, 2026

rustbot assigned epage Apr 22, 2026

epage reviewed Apr 22, 2026

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raushan728 force-pushed the fix-15296 branch from 1978dbb to bacfa17 Compare April 23, 2026 11:34

rustbot added the A-registries Area: registries label Apr 23, 2026

raushan728 requested a review from epage April 23, 2026 12:47

epage reviewed Apr 23, 2026

View reviewed changes

Comment thread src/cargo/core/resolver/errors.rs

epage reviewed Apr 23, 2026

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Comment thread src/cargo/core/resolver/errors.rs

epage reviewed Apr 23, 2026

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Comment thread src/cargo/core/resolver/errors.rs Outdated

epage reviewed Apr 23, 2026

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raushan728 force-pushed the fix-15296 branch 2 times, most recently from d4eb6f0 to d5f8d89 Compare April 24, 2026 06:09

fix(path): clarify error message when path dependency has wrong packa…

603d687

…ge (rust-lang#15296) When a path dependency points to a directory with a different package, show which package exists there and where the correct one can be found.

raushan728 force-pushed the fix-15296 branch from d5f8d89 to 603d687 Compare April 24, 2026 06:58

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raushan728 requested a review from epage April 26, 2026 14:48

epage reviewed Apr 27, 2026

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