Suggest the 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