Tweak output of import suggestions

When both `std::` and `core::` items are available, only suggest the
`std::` ones. We ensure that in `no_std` crates we suggest `core::`
items.

Ensure that the list of items suggested to be imported are always in the
order of local crate items, `std`/`core` items and finally foreign crate
items.

Tweak wording of import suggestion: if there are multiple items but they
are all of the same kind, we use the kind name and not the generic "items".

Fix #83564.

Author: estebank

compiler/rustc_resolve/src/diagnostics.rs

@@ -2783,33 +2783,56 @@ fn show_candidates(
     // by iterating through a hash map, so make sure they are ordered:
     for path_strings in [&mut accessible_path_strings, &mut inaccessible_path_strings] {
         path_strings.sort_by(|a, b| a.0.cmp(&b.0));
+        path_strings.dedup_by(|a, b| a.0 == b.0);
         let core_path_strings =
             path_strings.extract_if(|p| p.0.starts_with("core::")).collect::<Vec<_>>();
-        path_strings.extend(core_path_strings);
-        path_strings.dedup_by(|a, b| a.0 == b.0);
+        let std_path_strings =
+            path_strings.extract_if(|p| p.0.starts_with("std::")).collect::<Vec<_>>();
+        let foreign_crate_path_strings =
+            path_strings.extract_if(|p| !p.0.starts_with("crate::")).collect::<Vec<_>>();
+
+        // We list the `crate` local paths first.
+        // Then we list the `std`/`core` paths.
+        if std_path_strings.len() == core_path_strings.len() {
+            // Do not list `core::` paths if we are already listing the `std::` ones.
+            path_strings.extend(std_path_strings);
+        } else {
+            path_strings.extend(std_path_strings);
+            path_strings.extend(core_path_strings);
+        }
+        // List all paths from foreign crates last.
+        path_strings.extend(foreign_crate_path_strings);
     }
-    accessible_path_strings.sort();
 
     if !accessible_path_strings.is_empty() {
-        let (determiner, kind, name, through) =
-            if let [(name, descr, _, _, via_import)] = &accessible_path_strings[..] {
-                (
-                    "this",
-                    *descr,
-                    format!(" `{name}`"),
-                    if *via_import { " through its public re-export" } else { "" },
-                )
-            } else {
-                ("one of these", "items", String::new(), "")
-            };
+        let (determiner, kind, s, name, through) = if let [(name, descr, _, _, via_import)] =
+            &accessible_path_strings[..]
+        {
+            (
+                "this",
+                *descr,
+                "",
+                format!(" `{name}`"),
+                if *via_import { " through its public re-export" } else { "" },
+            )
+        } else {
+            let descr_set: FxHashSet<&str> =
+                accessible_path_strings.iter().map(|(_, descr, _, _, _)| *descr).collect();
+            let items =
+                if descr_set.len() == 1 { descr_set.into_iter().next().unwrap() } else { "item" };
+            let s = if items.ends_with('s') { "es" } else { "s" };
+
+            ("one of these", items, s, String::new(), "")
+        };
 
         let instead = if let Instead::Yes = instead { " instead" } else { "" };
         let mut msg = if let DiagMode::Pattern = mode {
             format!(
-                "if you meant to match on {kind}{instead}{name}, use the full path in the pattern",
+                "if you meant to match on {kind}{s}{instead}{name}, use the full path in the \
+                 pattern",
             )
         } else {
-            format!("consider importing {determiner} {kind}{through}{instead}")
+            format!("consider importing {determiner} {kind}{s}{through}{instead}")
         };
 
         for note in accessible_path_strings.iter().flat_map(|cand| cand.3.as_ref()) {

tests/ui/const-generics/issues/issue-82956.stderr

@@ -4,7 +4,7 @@ error[E0433]: failed to resolve: use of undeclared type `IntoIter`
 LL |         let mut iter = IntoIter::new(self);
    |                        ^^^^^^^^ use of undeclared type `IntoIter`
    |
-help: consider importing one of these items
+help: consider importing one of these structs
    |
 LL + use std::array::IntoIter;
    |

tests/ui/consts/const_refs_to_static-ice-121413.rs

@@ -5,12 +5,16 @@
 // ignore-tidy-linelength
 #![feature(const_refs_to_static)]
 const REF_INTERIOR_MUT: &usize = {
+    //~^ HELP consider importing this struct
     static FOO: Sync = AtomicUsize::new(0);
     //~^ ERROR failed to resolve: use of undeclared type `AtomicUsize`
     //~| WARN trait objects without an explicit `dyn` are deprecated
     //~| ERROR the size for values of type `(dyn Sync + 'static)` cannot be known at compilation time
     //~| ERROR the size for values of type `(dyn Sync + 'static)` cannot be known at compilation time
     //~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+    //~| HELP if this is an object-safe trait, use `dyn`
+    //~| HELP the trait `Sized` is not implemented for `(dyn Sync + 'static)`
+    //~| HELP the trait `Sized` is not implemented for `(dyn Sync + 'static)`
     unsafe { &*(&FOO as *const _ as *const usize) }
 };
 pub fn main() {}

tests/ui/consts/const_refs_to_static-ice-121413.stderr

@@ -1,5 +1,5 @@
 error[E0433]: failed to resolve: use of undeclared type `AtomicUsize`
-  --> $DIR/const_refs_to_static-ice-121413.rs:8:24
+  --> $DIR/const_refs_to_static-ice-121413.rs:9:24
    |
 LL |     static FOO: Sync = AtomicUsize::new(0);
    |                        ^^^^^^^^^^^ use of undeclared type `AtomicUsize`
@@ -10,7 +10,7 @@ LL + use std::sync::atomic::AtomicUsize;
    |
 
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/const_refs_to_static-ice-121413.rs:8:17
+  --> $DIR/const_refs_to_static-ice-121413.rs:9:17
    |
 LL |     static FOO: Sync = AtomicUsize::new(0);
    |                 ^^^^
@@ -24,15 +24,15 @@ LL |     static FOO: dyn Sync = AtomicUsize::new(0);
    |                 +++
 
 error[E0277]: the size for values of type `(dyn Sync + 'static)` cannot be known at compilation time
-  --> $DIR/const_refs_to_static-ice-121413.rs:8:17
+  --> $DIR/const_refs_to_static-ice-121413.rs:9:17
    |
 LL |     static FOO: Sync = AtomicUsize::new(0);
    |                 ^^^^ doesn't have a size known at compile-time
    |
    = help: the trait `Sized` is not implemented for `(dyn Sync + 'static)`
 
 error[E0277]: the size for values of type `(dyn Sync + 'static)` cannot be known at compilation time
-  --> $DIR/const_refs_to_static-ice-121413.rs:8:24
+  --> $DIR/const_refs_to_static-ice-121413.rs:9:24
    |
 LL |     static FOO: Sync = AtomicUsize::new(0);
    |                        ^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time

tests/ui/did_you_mean/issue-56028-there-is-an-enum-variant.stderr

@@ -22,7 +22,7 @@ error[E0425]: cannot find value `Set` in this scope
 LL | fn setup() -> Set { Set }
    |                     ^^^ not found in this scope
    |
-help: consider importing one of these items
+help: consider importing one of these unit variants
    |
 LL + use AffixHeart::Set;
    |

tests/ui/hygiene/extern-prelude-from-opaque-fail-2018.stderr

@@ -24,8 +24,7 @@ LL |         fn f() { my_core::mem::drop(0); }
 LL | a!();
    | ---- in this macro invocation
    |
-   = help: consider importing one of these items:
-           core::mem
+   = help: consider importing this module:
            std::mem
    = note: this error originates in the macro `a` (in Nightly builds, run with -Z macro-backtrace for more info)
 
@@ -35,9 +34,7 @@ error[E0433]: failed to resolve: use of undeclared crate or module `my_core`
 LL |     fn f() { my_core::mem::drop(0); }
    |              ^^^^^^^ use of undeclared crate or module `my_core`
    |
-help: consider importing one of these items
-   |
-LL +     use core::mem;
+help: consider importing this module
    |
 LL +     use std::mem;
    |

tests/ui/imports/cycle-import-in-std-1.stderr

@@ -4,8 +4,7 @@ error[E0432]: unresolved import `ops`
 LL | use ops::{self as std};
    |           ^^^^^^^^^^^ no external crate `ops`
    |
-   = help: consider importing one of these items instead:
-           core::ops
+   = help: consider importing this module instead:
            std::ops
 
 error: aborting due to 1 previous error

tests/ui/imports/cycle-import-in-std-2.stderr

@@ -4,8 +4,7 @@ error[E0432]: unresolved import `ops`
 LL | use ops::{self as std};
    |           ^^^^^^^^^^^ no external crate `ops`
    |
-   = help: consider importing one of these items instead:
-           core::ops
+   = help: consider importing this module instead:
            std::ops
 
 error: aborting due to 1 previous error

tests/ui/imports/import-alias-issue-121168.edition2018.stderr

@@ -4,7 +4,7 @@ error[E0412]: cannot find type `Foo` in this scope
 LL |     let _: Foo<i32> = todo!();
    |            ^^^ not found in this scope
    |
-help: consider importing one of these items
+help: consider importing one of these structs
    |
 LL + use crate::nice_crate_name::Foo;
    |

tests/ui/imports/import-alias-issue-121168.edition2021.stderr

@@ -4,7 +4,7 @@ error[E0412]: cannot find type `Foo` in this scope
 LL |     let _: Foo<i32> = todo!();
    |            ^^^ not found in this scope
    |
-help: consider importing one of these items
+help: consider importing one of these structs
    |
 LL + use crate::nice_crate_name::Foo;
    |