Add some tests for trimmed paths in diagnostics

tests/ui/trimmed-paths/auxiliary/doc_hidden_helper.rs

@@ -0,0 +1,18 @@
+//@ edition: 2024
+
+pub struct ActuallyPub {}
+#[doc(hidden)]
+pub struct DocHidden {}
+
+pub mod pub_mod {
+    pub struct ActuallyPubInPubMod {}
+    #[doc(hidden)]
+    pub struct DocHiddenInPubMod {}
+}
+
+#[doc(hidden)]
+pub mod hidden_mod {
+    pub struct ActuallyPubInHiddenMod {}
+    #[doc(hidden)]
+    pub struct DocHiddenInHiddenMod {}
+}

tests/ui/trimmed-paths/core-unicode.rs

@@ -0,0 +1,19 @@
+//@ edition: 2024
+
+// Test that the `#[doc(hidden)]` module `core::unicode` module does not
+// disqualify another item named `unicode` from path trimming in diagnostics.
+
+use core::marker::PhantomData;
+
+mod inner {
+    #[expect(non_camel_case_types)]
+    pub(crate) enum unicode {}
+}
+
+fn main() {
+    let PhantomData::<(inner::unicode, u32)> = PhantomData::<(u32, inner::unicode)>;
+    //~^ ERROR mismatched types [E0308]
+    //~| NOTE expected `PhantomData<(u32, unicode)>`, found `PhantomData<(unicode, u32)>`
+    //~| NOTE this expression has type `PhantomData<(u32, inner::unicode)>`
+    //~| NOTE expected struct `PhantomData<(u32, inner::unicode)>`
+}

tests/ui/trimmed-paths/core-unicode.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/core-unicode.rs:14:9
+   |
+LL |     let PhantomData::<(inner::unicode, u32)> = PhantomData::<(u32, inner::unicode)>;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^   ------------------------------------ this expression has type `PhantomData<(u32, inner::unicode)>`
+   |         |
+   |         expected `PhantomData<(u32, unicode)>`, found `PhantomData<(unicode, u32)>`
+   |
+   = note: expected struct `PhantomData<(u32, inner::unicode)>`
+              found struct `PhantomData<(inner::unicode, u32)>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.

tests/ui/trimmed-paths/doc-hidden.rs

@@ -0,0 +1,68 @@
+//@ edition: 2024
+//@ aux-crate: helper=doc_hidden_helper.rs
+
+// Test that `#[doc(hidden)]` items in other crates do not disqualify another
+// item with the same name from path trimming in diagnostics.
+
+// Declare several modules and types whose short names match those in the aux crate.
+//
+// Of these, only `ActuallyPub` and `ActuallyPubInPubMod` should be disqualified
+// from path trimming, because the other names only collide with `#[doc(hidden)]`
+// names.
+mod local {
+    pub(crate) struct ActuallyPub {}
+    pub(crate) struct DocHidden {}
+
+    pub(crate) mod pub_mod {
+        pub(crate) struct ActuallyPubInPubMod {}
+        pub(crate) struct DocHiddenInPubMod {}
+    }
+
+    pub(crate) mod hidden_mod {
+        pub(crate) struct ActuallyPubInHiddenMod {}
+        pub(crate) struct DocHiddenInHiddenMod {}
+    }
+}
+
+fn main() {
+    uses_local();
+    uses_helper();
+}
+
+fn uses_local() {
+    use local::{ActuallyPub, DocHidden};
+    use local::pub_mod::{ActuallyPubInPubMod, DocHiddenInPubMod};
+    use local::hidden_mod::{ActuallyPubInHiddenMod, DocHiddenInHiddenMod};
+
+    let _: (
+        //~^ NOTE expected due to this
+        ActuallyPub,
+        DocHidden,
+        ActuallyPubInPubMod,
+        DocHiddenInPubMod,
+        ActuallyPubInHiddenMod,
+        DocHiddenInHiddenMod,
+    ) = 3u32;
+    //~^ ERROR mismatched types [E0308]
+    //~| NOTE expected `(ActuallyPub, ..., ..., ..., ..., ...)`, found `u32`
+    //~| NOTE expected tuple `(local::ActuallyPub, local::DocHidden, local::pub_mod::ActuallyPubInPubMod, local::pub_mod::DocHiddenInPubMod, local::hidden_mod::ActuallyPubInHiddenMod, local::hidden_mod::DocHiddenInHiddenMod)`
+}
+
+fn uses_helper() {
+    use helper::{ActuallyPub, DocHidden};
+    use helper::pub_mod::{ActuallyPubInPubMod, DocHiddenInPubMod};
+    use helper::hidden_mod::{ActuallyPubInHiddenMod, DocHiddenInHiddenMod};
+
+    let _: (
+        //~^ NOTE expected due to this
+        ActuallyPub,
+        DocHidden,
+        ActuallyPubInPubMod,
+        DocHiddenInPubMod,
+        ActuallyPubInHiddenMod,
+        DocHiddenInHiddenMod,
+    ) = 3u32;
+    //~^ ERROR mismatched types [E0308]
+    //~| NOTE expected `(ActuallyPub, ..., ..., ..., ..., ...)`, found `u32`
+    //~| NOTE expected tuple `(doc_hidden_helper::ActuallyPub, doc_hidden_helper::DocHidden, doc_hidden_helper::pub_mod::ActuallyPubInPubMod, doc_hidden_helper::pub_mod::DocHiddenInPubMod, doc_hidden_helper::hidden_mod::ActuallyPubInHiddenMod, doc_hidden_helper::hidden_mod::DocHiddenInHiddenMod)`
+}

tests/ui/trimmed-paths/doc-hidden.stderr

@@ -0,0 +1,39 @@
+error[E0308]: mismatched types
+  --> $DIR/doc-hidden.rs:45:9
+   |
+LL |       let _: (
+   |  ____________-
+LL | |
+LL | |         ActuallyPub,
+LL | |         DocHidden,
+...  |
+LL | |         DocHiddenInHiddenMod,
+LL | |     ) = 3u32;
+   | |     -   ^^^^ expected `(ActuallyPub, ..., ..., ..., ..., ...)`, found `u32`
+   | |_____|
+   |       expected due to this
+   |
+   = note: expected tuple `(local::ActuallyPub, local::DocHidden, local::pub_mod::ActuallyPubInPubMod, local::pub_mod::DocHiddenInPubMod, local::hidden_mod::ActuallyPubInHiddenMod, local::hidden_mod::DocHiddenInHiddenMod)`
+               found type `u32`
+
+error[E0308]: mismatched types
+  --> $DIR/doc-hidden.rs:64:9
+   |
+LL |       let _: (
+   |  ____________-
+LL | |
+LL | |         ActuallyPub,
+LL | |         DocHidden,
+...  |
+LL | |         DocHiddenInHiddenMod,
+LL | |     ) = 3u32;
+   | |     -   ^^^^ expected `(ActuallyPub, ..., ..., ..., ..., ...)`, found `u32`
+   | |_____|
+   |       expected due to this
+   |
+   = note: expected tuple `(doc_hidden_helper::ActuallyPub, doc_hidden_helper::DocHidden, doc_hidden_helper::pub_mod::ActuallyPubInPubMod, doc_hidden_helper::pub_mod::DocHiddenInPubMod, doc_hidden_helper::hidden_mod::ActuallyPubInHiddenMod, doc_hidden_helper::hidden_mod::DocHiddenInHiddenMod)`
+               found type `u32`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.