pretty: trim paths of unique symbols

If a symbol name can only be imported from one place for a type, and
as long as it was not glob-imported anywhere in the current crate, we
can trim its printed path and print only the name.

This has wide implications on error messages with types, for example,
shortening `std::vec::Vec` to just `Vec`, as long as there is no other
`Vec` importable anywhere.

This adds a new '-Z trim-diagnostic-paths=false' option to control this
feature.

On the good path, with no diagnosis printed, we should try to avoid
issuing this query, so we need to prevent trimmed_def_paths query on
several cases.

This change also relies on a previous commit that differentiates
between `Debug` and `Display` on various rustc types, where the latter
is trimmed and presented to the user and the former is not.

4 files changed, 16 insertions, 16 deletions

diff --git a/src/test/ui/resolve/issue-5035-2.stderr b/src/test/ui/resolve/issue-5035-2.stderr
index 4ed93ad3279..5078ffbec73 100644
--- a/src/test/ui/resolve/issue-5035-2.stderr
+++ b/src/test/ui/resolve/issue-5035-2.stderr
@@ -4,7 +4,7 @@ error[E0277]: the size for values of type `(dyn I + 'static)` cannot be known at
 LL | fn foo(_x: K) {}
    |        ^^ doesn't have a size known at compile-time
    |
-   = help: the trait `std::marker::Sized` is not implemented for `(dyn I + 'static)`
+   = help: the trait `Sized` is not implemented for `(dyn I + 'static)`
    = help: unsized locals are gated as an unstable feature
 help: function arguments must have a statically known size, borrowed types always have a known size
    |
diff --git a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
index a324d04d394..9b59e415011 100644
--- a/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
+++ b/src/test/ui/resolve/issue-70736-async-fn-no-body-def-collector.stderr
@@ -57,7 +57,7 @@ LL |     async fn associated();
    |                          expected `()`, found opaque type
    |
    = note: expected fn pointer `fn()`
-              found fn pointer `fn() -> impl std::future::Future`
+              found fn pointer `fn() -> impl Future`
 
 error: aborting due to 6 previous errors
 
diff --git a/src/test/ui/resolve/name-clash-nullary.stderr b/src/test/ui/resolve/name-clash-nullary.stderr
index 2de0b6a4969..76c4b5914c1 100644
--- a/src/test/ui/resolve/name-clash-nullary.stderr
+++ b/src/test/ui/resolve/name-clash-nullary.stderr
@@ -4,10 +4,10 @@ error[E0308]: mismatched types
 LL |   let None: isize = 42;
    |       ^^^^  ----- expected due to this
    |       |
-   |       expected `isize`, found enum `std::option::Option`
+   |       expected `isize`, found enum `Option`
    |
    = note: expected type `isize`
-              found enum `std::option::Option<_>`
+              found enum `Option<_>`
 
 error: aborting due to previous error
 
diff --git a/src/test/ui/resolve/privacy-enum-ctor.stderr b/src/test/ui/resolve/privacy-enum-ctor.stderr
index f1ed7aaa867..32eff151196 100644
--- a/src/test/ui/resolve/privacy-enum-ctor.stderr
+++ b/src/test/ui/resolve/privacy-enum-ctor.stderr
@@ -260,15 +260,15 @@ error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:27:20
    |
 LL |             Fn(u8),
-   |             ------ fn(u8) -> m::n::Z {m::n::Z::Fn} defined here
+   |             ------ fn(u8) -> Z {Z::Fn} defined here
 ...
 LL |         let _: Z = Z::Fn;
-   |                -   ^^^^^ expected enum `m::n::Z`, found fn item
+   |                -   ^^^^^ expected enum `Z`, found fn item
    |                |
    |                expected due to this
    |
-   = note: expected enum `m::n::Z`
-           found fn item `fn(u8) -> m::n::Z {m::n::Z::Fn}`
+   = note: expected enum `Z`
+           found fn item `fn(u8) -> Z {Z::Fn}`
 help: use parentheses to instantiate this tuple variant
    |
 LL |         let _: Z = Z::Fn(_);
@@ -294,15 +294,15 @@ error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:43:16
    |
 LL |         Fn(u8),
-   |         ------ fn(u8) -> m::E {m::E::Fn} defined here
+   |         ------ fn(u8) -> E {E::Fn} defined here
 ...
 LL |     let _: E = m::E::Fn;
-   |            -   ^^^^^^^^ expected enum `m::E`, found fn item
+   |            -   ^^^^^^^^ expected enum `E`, found fn item
    |            |
    |            expected due to this
    |
-   = note: expected enum `m::E`
-           found fn item `fn(u8) -> m::E {m::E::Fn}`
+   = note: expected enum `E`
+           found fn item `fn(u8) -> E {E::Fn}`
 help: use parentheses to instantiate this tuple variant
    |
 LL |     let _: E = m::E::Fn(_);
@@ -328,15 +328,15 @@ error[E0308]: mismatched types
   --> $DIR/privacy-enum-ctor.rs:51:16
    |
 LL |         Fn(u8),
-   |         ------ fn(u8) -> m::E {m::E::Fn} defined here
+   |         ------ fn(u8) -> E {E::Fn} defined here
 ...
 LL |     let _: E = E::Fn;
-   |            -   ^^^^^ expected enum `m::E`, found fn item
+   |            -   ^^^^^ expected enum `E`, found fn item
    |            |
    |            expected due to this
    |
-   = note: expected enum `m::E`
-           found fn item `fn(u8) -> m::E {m::E::Fn}`
+   = note: expected enum `E`
+           found fn item `fn(u8) -> E {E::Fn}`
 help: use parentheses to instantiate this tuple variant
    |
 LL |     let _: E = E::Fn(_);