When suggesting to import an item, also suggest changing the path if appropriate

compiler/rustc_resolve/src/diagnostics.rs

@@ -117,7 +117,7 @@ impl<'a> Resolver<'a> {
     }
 
     fn report_with_use_injections(&mut self, krate: &Crate) {
-        for UseError { mut err, candidates, def_id, instead, suggestion } in
+        for UseError { mut err, candidates, def_id, instead, suggestion, path } in
             self.use_injections.drain(..)
         {
             let (span, found_use) = if let Some(def_id) = def_id.as_local() {
@@ -135,6 +135,7 @@ impl<'a> Resolver<'a> {
                     if instead { Instead::Yes } else { Instead::No },
                     found_use,
                     IsPattern::No,
+                    path,
                 );
             } else if let Some((span, msg, sugg, appl)) = suggestion {
                 err.span_suggestion(span, msg, sugg, appl);
@@ -702,6 +703,7 @@ impl<'a> Resolver<'a> {
                         Instead::No,
                         FoundUse::Yes,
                         IsPattern::Yes,
+                        vec![],
                     );
                 }
                 err
@@ -1482,6 +1484,7 @@ impl<'a> Resolver<'a> {
             Instead::No,
             FoundUse::Yes,
             IsPattern::No,
+            vec![],
         );
 
         if macro_kind == MacroKind::Derive && (ident.name == sym::Send || ident.name == sym::Sync) {
@@ -2448,6 +2451,7 @@ fn show_candidates(
     instead: Instead,
     found_use: FoundUse,
     is_pattern: IsPattern,
+    path: Vec<Segment>,
 ) {
     if candidates.is_empty() {
         return;
@@ -2515,6 +2519,14 @@ fn show_candidates(
                 accessible_path_strings.into_iter().map(|a| a.0),
                 Applicability::MaybeIncorrect,
             );
+            if let [first, .., last] = &path[..] {
+                err.span_suggestion_verbose(
+                    first.ident.span.until(last.ident.span),
+                    &format!("if you import `{}`, refer to it directly", last.ident),
+                    String::new(),
+                    Applicability::Unspecified,
+                );
+            }
         } else {
             msg.push(':');
 

compiler/rustc_resolve/src/late.rs

@@ -2682,6 +2682,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                     def_id,
                     instead,
                     suggestion,
+                    path: path.into(),
                 });
             }
 
@@ -2745,6 +2746,7 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                     def_id,
                     instead: false,
                     suggestion: None,
+                    path: path.into(),
                 });
             } else {
                 err.cancel();

compiler/rustc_resolve/src/lib.rs

@@ -696,6 +696,9 @@ struct UseError<'a> {
     instead: bool,
     /// Extra free-form suggestion.
     suggestion: Option<(Span, &'static str, String, Applicability)>,
+    /// Path `Segment`s at the place of use that failed. Used for accurate suggestion after telling
+    /// the user to import the item directly.
+    path: Vec<Segment>,
 }
 
 #[derive(Clone, Copy, PartialEq, Debug)]

src/test/ui/macros/macro-outer-attributes.stderr

@@ -8,6 +8,11 @@ help: consider importing this function
    |
 LL | use b::bar;
    |
+help: if you import `bar`, refer to it directly
+   |
+LL -     a::bar();
+LL +     bar();
+   | 
 
 error: aborting due to previous error
 

src/test/ui/namespace/namespace-mix.stderr

@@ -18,6 +18,11 @@ LL | use m2::S;
    |
 LL | use xm2::S;
    |
+help: if you import `S`, refer to it directly
+   |
+LL -     check(m1::S);
+LL +     check(S);
+   | 
 
 error[E0423]: expected value, found type alias `xm1::S`
   --> $DIR/namespace-mix.rs:40:11
@@ -41,6 +46,11 @@ LL | use m2::S;
    |
 LL | use xm2::S;
    |
+help: if you import `S`, refer to it directly
+   |
+LL -     check(xm1::S);
+LL +     check(S);
+   | 
 
 error[E0423]: expected value, found struct variant `m7::V`
   --> $DIR/namespace-mix.rs:100:11
@@ -67,6 +77,11 @@ LL | use m8::V;
    |
 LL | use xm8::V;
    |
+help: if you import `V`, refer to it directly
+   |
+LL -     check(m7::V);
+LL +     check(V);
+   | 
 
 error[E0423]: expected value, found struct variant `xm7::V`
   --> $DIR/namespace-mix.rs:106:11
@@ -95,6 +110,11 @@ LL | use m8::V;
    |
 LL | use xm8::V;
    |
+help: if you import `V`, refer to it directly
+   |
+LL -     check(xm7::V);
+LL +     check(V);
+   | 
 
 error[E0277]: the trait bound `c::Item: Impossible` is not satisfied
   --> $DIR/namespace-mix.rs:33:11

src/test/ui/parser/circular_modules_main.stderr

@@ -14,6 +14,11 @@ help: consider importing this function
    |
 LL | use hi_str;
    |
+help: if you import `hi_str`, refer to it directly
+   |
+LL -     println!("{}", circular_modules_main::hi_str());
+LL +     println!("{}", hi_str());
+   | 
 
 error: aborting due to 2 previous errors
 

src/test/ui/resolve/enums-are-namespaced-xc.stderr

@@ -8,6 +8,11 @@ help: consider importing this unit variant
    |
 LL | use namespaced_enums::Foo::A;
    |
+help: if you import `A`, refer to it directly
+   |
+LL -     let _ = namespaced_enums::A;
+LL +     let _ = A;
+   | 
 
 error[E0425]: cannot find function, tuple struct or tuple variant `B` in crate `namespaced_enums`
   --> $DIR/enums-are-namespaced-xc.rs:7:31
@@ -19,6 +24,11 @@ help: consider importing this tuple variant
    |
 LL | use namespaced_enums::Foo::B;
    |
+help: if you import `B`, refer to it directly
+   |
+LL -     let _ = namespaced_enums::B(10);
+LL +     let _ = B(10);
+   | 
 
 error[E0422]: cannot find struct, variant or union type `C` in crate `namespaced_enums`
   --> $DIR/enums-are-namespaced-xc.rs:9:31
@@ -30,6 +40,11 @@ help: consider importing this variant
    |
 LL | use namespaced_enums::Foo::C;
    |
+help: if you import `C`, refer to it directly
+   |
+LL -     let _ = namespaced_enums::C { a: 10 };
+LL +     let _ = C { a: 10 };
+   | 
 
 error: aborting due to 3 previous errors
 

src/test/ui/resolve/issue-50599.stderr

@@ -10,6 +10,11 @@ LL | use std::f32::consts::LOG10_2;
    |
 LL | use std::f64::consts::LOG10_2;
    |
+help: if you import `LOG10_2`, refer to it directly
+   |
+LL -     const M: usize = (f64::from(N) * std::f64::LOG10_2) as usize;
+LL +     const M: usize = (f64::from(N) * LOG10_2) as usize;
+   | 
 
 error: aborting due to previous error
 

src/test/ui/resolve/missing-in-namespace.stderr

@@ -8,6 +8,11 @@ help: consider importing this struct
    |
 LL | use std::collections::HashMap;
    |
+help: if you import `HashMap`, refer to it directly
+   |
+LL -     let _map = std::hahmap::HashMap::new();
+LL +     let _map = HashMap::new();
+   | 
 
 error: aborting due to previous error
 

src/test/ui/resolve/privacy-enum-ctor.stderr

@@ -105,6 +105,11 @@ LL | use std::f32::consts::E;
    |
 LL | use std::f64::consts::E;
    |
+help: if you import `E`, refer to it directly
+   |
+LL -     let _: E = m::E;
+LL +     let _: E = E;
+   | 
 
 error[E0423]: expected value, found struct variant `m::E::Struct`
   --> $DIR/privacy-enum-ctor.rs:45:16

src/test/ui/resolve/resolve-primitive-fallback.stderr

@@ -14,6 +14,11 @@ help: consider importing this builtin type
    |
 LL | use std::primitive::u8;
    |
+help: if you import `u8`, refer to it directly
+   |
+LL -     let _: ::u8;
+LL +     let _: u8;
+   | 
 
 error[E0061]: this function takes 0 arguments but 1 argument was supplied
   --> $DIR/resolve-primitive-fallback.rs:3:5

src/test/ui/trait-bounds/shadowed-path-in-trait-bound-suggestion.fixed

@@ -0,0 +1,16 @@
+// run-rustfix
+#![allow(non_snake_case)]
+mod A {
+    pub trait Trait {}
+    impl Trait for i32 {}
+}
+
+mod B {
+    use A::Trait;
+
+pub struct A<H: Trait>(pub H); //~ ERROR cannot find trait
+}
+
+fn main() {
+    let _ = B::A(42);
+}

src/test/ui/trait-bounds/shadowed-path-in-trait-bound-suggestion.rs

@@ -0,0 +1,14 @@
+// run-rustfix
+#![allow(non_snake_case)]
+mod A {
+    pub trait Trait {}
+    impl Trait for i32 {}
+}
+
+mod B {
+    pub struct A<H: A::Trait>(pub H); //~ ERROR cannot find trait
+}
+
+fn main() {
+    let _ = B::A(42);
+}

src/test/ui/trait-bounds/shadowed-path-in-trait-bound-suggestion.stderr

@@ -0,0 +1,19 @@
+error[E0405]: cannot find trait `Trait` in `A`
+  --> $DIR/shadowed-path-in-trait-bound-suggestion.rs:9:24
+   |
+LL |     pub struct A<H: A::Trait>(pub H);
+   |                        ^^^^^ not found in `A`
+   |
+help: consider importing this trait
+   |
+LL |     use A::Trait;
+   |
+help: if you import `Trait`, refer to it directly
+   |
+LL -     pub struct A<H: A::Trait>(pub H);
+LL +     pub struct A<H: Trait>(pub H);
+   | 
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0405`.