Suggest path separator when a dot is used on a trait

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -985,27 +985,45 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         let ns = source.namespace();
         let is_expected = &|res| source.is_expected(res);
 
-        let path_sep = |err: &mut Diagnostic, expr: &Expr| match expr.kind {
-            ExprKind::Field(_, ident) => {
+        let path_sep = |err: &mut Diagnostic, expr: &Expr, kind: DefKind| {
+            const MESSAGE: &str = "use the path separator to refer to an item";
+
+            let (lhs_span, rhs_span) = match &expr.kind {
+                ExprKind::Field(base, ident) => (base.span, ident.span),
+                ExprKind::MethodCall(_, receiver, _, span) => (receiver.span, *span),
+                _ => return false,
+            };
+
+            if lhs_span.eq_ctxt(rhs_span) {
                 err.span_suggestion(
-                    expr.span,
-                    "use the path separator to refer to an item",
-                    format!("{}::{}", path_str, ident),
+                    lhs_span.between(rhs_span),
+                    MESSAGE,
+                    "::",
                     Applicability::MaybeIncorrect,
                 );
                 true
-            }
-            ExprKind::MethodCall(ref segment, ..) => {
-                let span = expr.span.with_hi(segment.ident.span.hi());
-                err.span_suggestion(
-                    span,
-                    "use the path separator to refer to an item",
-                    format!("{}::{}", path_str, segment.ident),
+            } else if kind == DefKind::Struct
+            && let Some(lhs_source_span) = lhs_span.find_ancestor_inside(expr.span)
+            && let Ok(snippet) = self.r.session.source_map().span_to_snippet(lhs_source_span)
+            {
+                // The LHS is a type that originates from a macro call.
+                // We have to add angle brackets around it.
+
+                err.span_suggestion_verbose(
+                    lhs_source_span.until(rhs_span),
+                    MESSAGE,
+                    format!("<{snippet}>::"),
                     Applicability::MaybeIncorrect,
                 );
                 true
+            } else {
+                // Either we were unable to obtain the source span / the snippet or
+                // the LHS originates from a macro call and it is not a type and thus
+                // there is no way to replace `.` with `::` and still somehow suggest
+                // valid Rust code.
+
+                false
             }
-            _ => false,
         };
 
         let find_span = |source: &PathSource<'_>, err: &mut Diagnostic| {
@@ -1027,7 +1045,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
             match source {
                 PathSource::Expr(Some(
                     parent @ Expr { kind: ExprKind::Field(..) | ExprKind::MethodCall(..), .. },
-                )) if path_sep(err, &parent) => {}
+                )) if path_sep(err, &parent, DefKind::Struct) => {}
                 PathSource::Expr(
                     None
                     | Some(Expr {
@@ -1143,8 +1161,11 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                     }
                 }
             }
-            (Res::Def(DefKind::Mod, _), PathSource::Expr(Some(parent))) => {
-                if !path_sep(err, &parent) {
+            (
+                Res::Def(kind @ (DefKind::Mod | DefKind::Trait), _),
+                PathSource::Expr(Some(parent)),
+            ) => {
+                if !path_sep(err, &parent, kind) {
                     return false;
                 }
             }

src/test/ui/resolve/issue-100365.rs

@@ -0,0 +1,50 @@
+fn main() {
+    let addr = Into::<std::net::IpAddr>.into([127, 0, 0, 1]);
+    //~^ ERROR expected value, found trait `Into`
+    //~| HELP use the path separator
+
+    let _ = Into.into(());
+    //~^ ERROR expected value, found trait `Into`
+    //~| HELP use the path separator
+
+    let _ = Into::<()>.into;
+    //~^ ERROR expected value, found trait `Into`
+    //~| HELP use the path separator
+}
+
+macro_rules! Trait {
+    () => {
+        ::std::iter::Iterator
+        //~^ ERROR expected value, found trait `std::iter::Iterator`
+        //~| ERROR expected value, found trait `std::iter::Iterator`
+    };
+}
+
+macro_rules! create {
+    () => {
+        Into::<String>.into("")
+        //~^ ERROR expected value, found trait `Into`
+        //~| HELP use the path separator
+    };
+}
+
+fn interaction_with_macros() {
+    //
+    // Note that if the receiver is a macro call, we do not want to suggest to replace
+    // `.` with `::` as that would be a syntax error.
+    // Since the receiver is a trait and not a type, we cannot suggest to surround
+    // it with angle brackets. It would be interpreted as a trait object type void of
+    // `dyn` which is most likely not what the user intended to write.
+    // `<_ as Trait!()>::` is also not an option as it's equally syntactically invalid.
+    //
+
+    Trait!().map(std::convert::identity); // no `help` here!
+
+    Trait!().map; // no `help` here!
+
+    //
+    // Ensure that the suggestion is shown for expressions inside of macro definitions.
+    //
+
+    let _ = create!();
+}

src/test/ui/resolve/issue-100365.stderr

@@ -0,0 +1,54 @@
+error[E0423]: expected value, found trait `Into`
+  --> $DIR/issue-100365.rs:2:16
+   |
+LL |     let addr = Into::<std::net::IpAddr>.into([127, 0, 0, 1]);
+   |                ^^^^^^^^^^^^^^^^^^^^^^^^- help: use the path separator to refer to an item: `::`
+
+error[E0423]: expected value, found trait `Into`
+  --> $DIR/issue-100365.rs:6:13
+   |
+LL |     let _ = Into.into(());
+   |             ^^^^- help: use the path separator to refer to an item: `::`
+
+error[E0423]: expected value, found trait `Into`
+  --> $DIR/issue-100365.rs:10:13
+   |
+LL |     let _ = Into::<()>.into;
+   |             ^^^^^^^^^^- help: use the path separator to refer to an item: `::`
+
+error[E0423]: expected value, found trait `std::iter::Iterator`
+  --> $DIR/issue-100365.rs:17:9
+   |
+LL |         ::std::iter::Iterator
+   |         ^^^^^^^^^^^^^^^^^^^^^ not a value
+...
+LL |     Trait!().map(std::convert::identity); // no `help` here!
+   |     -------- in this macro invocation
+   |
+   = note: this error originates in the macro `Trait` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found trait `std::iter::Iterator`
+  --> $DIR/issue-100365.rs:17:9
+   |
+LL |         ::std::iter::Iterator
+   |         ^^^^^^^^^^^^^^^^^^^^^ not a value
+...
+LL |     Trait!().map; // no `help` here!
+   |     -------- in this macro invocation
+   |
+   = note: this error originates in the macro `Trait` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found trait `Into`
+  --> $DIR/issue-100365.rs:25:9
+   |
+LL |         Into::<String>.into("")
+   |         ^^^^^^^^^^^^^^- help: use the path separator to refer to an item: `::`
+...
+LL |     let _ = create!();
+   |             --------- in this macro invocation
+   |
+   = note: this error originates in the macro `create` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0423`.

src/test/ui/resolve/issue-22692.rs

@@ -1,3 +1,60 @@
 fn main() {
-    let _ = String.new(); //~ ERROR expected value, found struct `String`
+    let _ = String.new();
+    //~^ ERROR expected value, found struct `String`
+    //~| HELP use the path separator
+
+    let _ = String.default;
+    //~^ ERROR expected value, found struct `String`
+    //~| HELP use the path separator
+
+    let _ = Vec::<()>.with_capacity(1);
+    //~^ ERROR expected value, found struct `Vec`
+    //~| HELP use the path separator
+}
+
+macro_rules! Type {
+    () => {
+        ::std::cell::Cell
+        //~^ ERROR expected value, found struct `std::cell::Cell`
+        //~| ERROR expected value, found struct `std::cell::Cell`
+        //~| ERROR expected value, found struct `std::cell::Cell`
+    };
+}
+
+macro_rules! create {
+    (type method) => {
+        Vec.new()
+        //~^ ERROR expected value, found struct `Vec`
+        //~| HELP use the path separator
+    };
+    (type field) => {
+        Vec.new
+        //~^ ERROR expected value, found struct `Vec`
+        //~| HELP use the path separator
+    };
+    (macro method) => {
+        Type!().new(0)
+        //~^ HELP use the path separator
+    };
+}
+
+fn interaction_with_macros() {
+    //
+    // Verify that we do not only suggest to replace `.` with `::` if the receiver is a
+    // macro call but that we also correctly suggest to surround it with angle brackets.
+    //
+
+    Type!().get();
+    //~^ HELP use the path separator
+
+    Type! {}.get;
+    //~^ HELP use the path separator
+
+    //
+    // Ensure that the suggestion is shown for expressions inside of macro definitions.
+    //
+
+    let _ = create!(type method);
+    let _ = create!(type field);
+    let _ = create!(macro method);
 }

src/test/ui/resolve/issue-22692.stderr

@@ -2,10 +2,87 @@ error[E0423]: expected value, found struct `String`
   --> $DIR/issue-22692.rs:2:13
    |
 LL |     let _ = String.new();
-   |             ^^^^^^----
-   |             |
-   |             help: use the path separator to refer to an item: `String::new`
+   |             ^^^^^^- help: use the path separator to refer to an item: `::`
 
-error: aborting due to previous error
+error[E0423]: expected value, found struct `String`
+  --> $DIR/issue-22692.rs:6:13
+   |
+LL |     let _ = String.default;
+   |             ^^^^^^- help: use the path separator to refer to an item: `::`
+
+error[E0423]: expected value, found struct `Vec`
+  --> $DIR/issue-22692.rs:10:13
+   |
+LL |     let _ = Vec::<()>.with_capacity(1);
+   |             ^^^^^^^^^- help: use the path separator to refer to an item: `::`
+
+error[E0423]: expected value, found struct `std::cell::Cell`
+  --> $DIR/issue-22692.rs:17:9
+   |
+LL |         ::std::cell::Cell
+   |         ^^^^^^^^^^^^^^^^^
+...
+LL |     Type!().get();
+   |     ------- in this macro invocation
+   |
+   = note: this error originates in the macro `Type` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: use the path separator to refer to an item
+   |
+LL |     <Type!()>::get();
+   |     ~~~~~~~~~~~
+
+error[E0423]: expected value, found struct `std::cell::Cell`
+  --> $DIR/issue-22692.rs:17:9
+   |
+LL |         ::std::cell::Cell
+   |         ^^^^^^^^^^^^^^^^^
+...
+LL |     Type! {}.get;
+   |     -------- in this macro invocation
+   |
+   = note: this error originates in the macro `Type` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: use the path separator to refer to an item
+   |
+LL |     <Type! {}>::get;
+   |     ~~~~~~~~~~~~
+
+error[E0423]: expected value, found struct `Vec`
+  --> $DIR/issue-22692.rs:26:9
+   |
+LL |         Vec.new()
+   |         ^^^- help: use the path separator to refer to an item: `::`
+...
+LL |     let _ = create!(type method);
+   |             -------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `create` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found struct `Vec`
+  --> $DIR/issue-22692.rs:31:9
+   |
+LL |         Vec.new
+   |         ^^^- help: use the path separator to refer to an item: `::`
+...
+LL |     let _ = create!(type field);
+   |             ------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `create` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found struct `std::cell::Cell`
+  --> $DIR/issue-22692.rs:17:9
+   |
+LL |         ::std::cell::Cell
+   |         ^^^^^^^^^^^^^^^^^
+...
+LL |     let _ = create!(macro method);
+   |             --------------------- in this macro invocation
+   |
+   = note: this error originates in the macro `Type` which comes from the expansion of the macro `create` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: use the path separator to refer to an item
+   |
+LL |         <Type!()>::new(0)
+   |         ~~~~~~~~~~~
+
+error: aborting due to 8 previous errors
 
 For more information about this error, try `rustc --explain E0423`.

src/test/ui/resolve/suggest-path-for-tuple-struct.stderr

@@ -2,17 +2,13 @@ error[E0423]: expected value, found struct `SomeTupleStruct`
   --> $DIR/suggest-path-for-tuple-struct.rs:22:13
    |
 LL |     let _ = SomeTupleStruct.new();
-   |             ^^^^^^^^^^^^^^^----
-   |             |
-   |             help: use the path separator to refer to an item: `SomeTupleStruct::new`
+   |             ^^^^^^^^^^^^^^^- help: use the path separator to refer to an item: `::`
 
 error[E0423]: expected value, found struct `SomeRegularStruct`
   --> $DIR/suggest-path-for-tuple-struct.rs:24:13
    |
 LL |     let _ = SomeRegularStruct.new();
-   |             ^^^^^^^^^^^^^^^^^----
-   |             |
-   |             help: use the path separator to refer to an item: `SomeRegularStruct::new`
+   |             ^^^^^^^^^^^^^^^^^- help: use the path separator to refer to an item: `::`
 
 error: aborting due to 2 previous errors
 

src/test/ui/resolve/suggest-path-instead-of-mod-dot-item.rs

@@ -16,44 +16,96 @@ pub mod a {
 fn h1() -> i32 {
     a.I
     //~^ ERROR expected value, found module `a`
+    //~| HELP use the path separator
 }
 
 fn h2() -> i32 {
     a.g()
     //~^ ERROR expected value, found module `a`
+    //~| HELP use the path separator
 }
 
 fn h3() -> i32 {
     a.b.J
     //~^ ERROR expected value, found module `a`
+    //~| HELP use the path separator
 }
 
 fn h4() -> i32 {
     a::b.J
     //~^ ERROR expected value, found module `a::b`
+    //~| HELP a constant with a similar name exists
+    //~| HELP use the path separator
 }
 
 fn h5() {
     a.b.f();
     //~^ ERROR expected value, found module `a`
+    //~| HELP use the path separator
     let v = Vec::new();
     v.push(a::b);
     //~^ ERROR expected value, found module `a::b`
+    //~| HELP a constant with a similar name exists
 }
 
 fn h6() -> i32 {
     a::b.f()
     //~^ ERROR expected value, found module `a::b`
+    //~| HELP a constant with a similar name exists
+    //~| HELP use the path separator
 }
 
 fn h7() {
     a::b
     //~^ ERROR expected value, found module `a::b`
+    //~| HELP a constant with a similar name exists
 }
 
 fn h8() -> i32 {
     a::b()
     //~^ ERROR expected function, found module `a::b`
+    //~| HELP a constant with a similar name exists
+}
+
+macro_rules! module {
+    () => {
+        a
+        //~^ ERROR expected value, found module `a`
+        //~| ERROR expected value, found module `a`
+    };
+}
+
+macro_rules! create {
+    (method) => {
+        a.f()
+        //~^ ERROR expected value, found module `a`
+        //~| HELP use the path separator
+    };
+    (field) => {
+        a.f
+        //~^ ERROR expected value, found module `a`
+        //~| HELP use the path separator
+    };
+}
+
+fn h9() {
+    //
+    // Note that if the receiver is a macro call, we do not want to suggest to replace
+    // `.` with `::` as that would be a syntax error.
+    // Since the receiver is a module and not a type, we cannot suggest to surround
+    // it with angle brackets.
+    //
+
+    module!().g::<()>(); // no `help` here!
+
+    module!().g; // no `help` here!
+
+    //
+    // Ensure that the suggestion is shown for expressions inside of macro definitions.
+    //
+
+    let _ = create!(method);
+    let _ = create!(field);
 }
 
 fn main() {}

src/test/ui/resolve/suggest-path-instead-of-mod-dot-item.stderr

@@ -2,28 +2,22 @@ error[E0423]: expected value, found module `a`
   --> $DIR/suggest-path-instead-of-mod-dot-item.rs:17:5
    |
 LL |     a.I
-   |     ^--
-   |     |
-   |     help: use the path separator to refer to an item: `a::I`
+   |     ^- help: use the path separator to refer to an item: `::`
 
 error[E0423]: expected value, found module `a`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:22:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:23:5
    |
 LL |     a.g()
-   |     ^--
-   |     |
-   |     help: use the path separator to refer to an item: `a::g`
+   |     ^- help: use the path separator to refer to an item: `::`
 
 error[E0423]: expected value, found module `a`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:27:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:29:5
    |
 LL |     a.b.J
-   |     ^--
-   |     |
-   |     help: use the path separator to refer to an item: `a::b`
+   |     ^- help: use the path separator to refer to an item: `::`
 
 error[E0423]: expected value, found module `a::b`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:32:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:35:5
    |
 LL |     pub const I: i32 = 1;
    |     --------------------- similarly named constant `I` defined here
@@ -34,22 +28,20 @@ LL |     a::b.J
 help: use the path separator to refer to an item
    |
 LL |     a::b::J
-   |
+   |         ~~
 help: a constant with a similar name exists
    |
 LL |     a::I.J
    |        ~
 
 error[E0423]: expected value, found module `a`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:37:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:42:5
    |
 LL |     a.b.f();
-   |     ^--
-   |     |
-   |     help: use the path separator to refer to an item: `a::b`
+   |     ^- help: use the path separator to refer to an item: `::`
 
 error[E0423]: expected value, found module `a::b`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:40:12
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:46:12
    |
 LL |     pub const I: i32 = 1;
    |     --------------------- similarly named constant `I` defined here
@@ -60,7 +52,7 @@ LL |     v.push(a::b);
    |               help: a constant with a similar name exists: `I`
 
 error[E0423]: expected value, found module `a::b`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:45:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:52:5
    |
 LL |     pub const I: i32 = 1;
    |     --------------------- similarly named constant `I` defined here
@@ -71,14 +63,14 @@ LL |     a::b.f()
 help: use the path separator to refer to an item
    |
 LL |     a::b::f()
-   |     ~~~~~~~
+   |         ~~
 help: a constant with a similar name exists
    |
 LL |     a::I.f()
    |        ~
 
 error[E0423]: expected value, found module `a::b`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:50:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:59:5
    |
 LL |     pub const I: i32 = 1;
    |     --------------------- similarly named constant `I` defined here
@@ -89,7 +81,7 @@ LL |     a::b
    |        help: a constant with a similar name exists: `I`
 
 error[E0423]: expected function, found module `a::b`
-  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:55:5
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:65:5
    |
 LL |     pub const I: i32 = 1;
    |     --------------------- similarly named constant `I` defined here
@@ -99,6 +91,50 @@ LL |     a::b()
    |        |
    |        help: a constant with a similar name exists: `I`
 
-error: aborting due to 9 previous errors
+error[E0423]: expected value, found module `a`
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:72:9
+   |
+LL |         a
+   |         ^ not a value
+...
+LL |     module!().g::<()>(); // no `help` here!
+   |     --------- in this macro invocation
+   |
+   = note: this error originates in the macro `module` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found module `a`
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:72:9
+   |
+LL |         a
+   |         ^ not a value
+...
+LL |     module!().g; // no `help` here!
+   |     --------- in this macro invocation
+   |
+   = note: this error originates in the macro `module` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found module `a`
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:80:9
+   |
+LL |         a.f()
+   |         ^- help: use the path separator to refer to an item: `::`
+...
+LL |     let _ = create!(method);
+   |             --------------- in this macro invocation
+   |
+   = note: this error originates in the macro `create` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0423]: expected value, found module `a`
+  --> $DIR/suggest-path-instead-of-mod-dot-item.rs:85:9
+   |
+LL |         a.f
+   |         ^- help: use the path separator to refer to an item: `::`
+...
+LL |     let _ = create!(field);
+   |             -------------- in this macro invocation
+   |
+   = note: this error originates in the macro `create` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 13 previous errors
 
 For more information about this error, try `rustc --explain E0423`.

src/test/ui/suggestions/assoc-const-as-field.stderr

@@ -2,9 +2,7 @@ error[E0423]: expected value, found struct `Mod::Foo`
   --> $DIR/assoc-const-as-field.rs:11:9
    |
 LL |     foo(Mod::Foo.Bar);
-   |         ^^^^^^^^----
-   |         |
-   |         help: use the path separator to refer to an item: `Mod::Foo::Bar`
+   |         ^^^^^^^^- help: use the path separator to refer to an item: `::`
 
 error: aborting due to previous error