Improve E0603 suggestions for private grouped imports

compiler/rustc_resolve/src/diagnostics/impls.rs

@@ -2519,17 +2519,57 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         *path = Path { span: path.span, segments: new_segments };
     }
 
+    fn expand_span_to_surrounding_comma(
+        source_text: &str,
+        ident_start: usize,
+        ident_end: usize,
+    ) -> (usize, usize) {
+        // A trailing comma is consumed to keep the remaining group valid.
+        let after_ident = &source_text[ident_end..];
+        let trimmed = after_ident.trim_start();
+        if trimmed.starts_with(',') {
+            let comma_pos = ident_end + (after_ident.len() - trimmed.len());
+            let after_comma = &source_text[comma_pos + 1..];
+            let next_non_ws =
+                after_comma.find(|c: char| !c.is_whitespace()).unwrap_or(after_comma.len());
+            return (ident_start, comma_pos + 1 + next_non_ws);
+        }
+
+        // If there is no trailing comma, this must be the last item in the group,
+        // so we consume the leading comma instead.
+        let before_ident = &source_text[..ident_start];
+        let trimmed = before_ident.trim_end();
+        if trimmed.ends_with(',') {
+            let comma_pos = trimmed.len() - 1;
+            return (comma_pos, ident_end);
+        }
+
+        (ident_start, ident_end)
+    }
+
+    fn get_indentation(sm: &SourceMap, span: Span) -> String {
+        let line_span = sm.span_extend_to_line(span.shrink_to_lo());
+        sm.span_to_snippet(line_span)
+            .map(|line| {
+                let non_ws = line.find(|c: char| !c.is_whitespace()).unwrap_or(line.len());
+                line[..non_ws].to_string()
+            })
+            .unwrap_or_default()
+    }
+
     fn report_privacy_error(&mut self, privacy_error: &PrivacyError<'ra>) {
         let PrivacyError {
             ident,
             decl,
             outermost_res,
             parent_scope,
-            single_nested,
+            root_span,
             dedup_span,
             ref source,
         } = *privacy_error;
 
+        let single_nested = dedup_span != root_span;
+
         let res = decl.res();
         let ctor_fields_span = self.ctor_fields_span(decl);
         let plain_descr = res.descr().to_string();
@@ -2804,6 +2844,84 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 err.subdiagnostic(sugg);
                 break;
             }
+        } else if single_nested
+            && !shown_candidates
+            && !outermost_res.is_some_and(|(_, outer)| outer.span != ident.span)
+        {
+            sugg_paths.sort_by_key(|(p, reexport)| (p.len(), p[0].name == sym::core, *reexport));
+            for (sugg, reexport) in sugg_paths {
+                if sugg.len() <= 1 {
+                    continue;
+                }
+                let path = join_path_idents(sugg);
+                let Ok(source_text) = self.tcx.sess.source_map().span_to_snippet(root_span) else {
+                    continue;
+                };
+
+                let lo_offset = (ident.span.lo() - root_span.lo()).0 as usize;
+                let hi_offset = (ident.span.hi() - root_span.lo()).0 as usize;
+
+                if lo_offset > source_text.len() || hi_offset > source_text.len() {
+                    continue;
+                }
+
+                let (start, end) =
+                    Self::expand_span_to_surrounding_comma(&source_text, lo_offset, hi_offset);
+
+                let mut replacement = String::new();
+                replacement.push_str(&source_text[..start]);
+                replacement.push_str(&source_text[end..]);
+
+                // An empty group like `foo::{}` is invalid syntax.
+                if replacement.contains("{}") {
+                    let msg = if reexport {
+                        format!("import `{ident}` through the re-export")
+                    } else {
+                        format!("import `{ident}` directly")
+                    };
+
+                    let line_span = self.tcx.sess.source_map().span_extend_to_line(root_span);
+                    let indentation = Self::get_indentation(self.tcx.sess.source_map(), root_span);
+                    let suggestion_text = format!("{indentation}use {path};");
+                    err.multipart_suggestion(
+                        msg,
+                        vec![(line_span, suggestion_text)],
+                        Applicability::MachineApplicable,
+                    );
+                    break;
+                }
+
+                // Braces are not needed when only one item remains in the group.
+                if let Some(open) = replacement.find('{') {
+                    if let Some(close) = replacement.rfind('}') {
+                        let inner = replacement[open + 1..close].trim();
+                        if !inner.contains(',') && !inner.is_empty() {
+                            replacement = format!("{}{}", replacement[..open].trim_end(), inner);
+                        }
+                    }
+                }
+
+                let msg = if reexport {
+                    format!("import `{ident}` through the re-export")
+                } else {
+                    format!("import `{ident}` directly")
+                };
+
+                // The new import is placed on its own line, so we match the current indentation.
+                let indentation = Self::get_indentation(self.tcx.sess.source_map(), root_span);
+
+                // `root_span` doesn't include the `use` keyword, so inserting just before it
+                // avoids duplicating the keyword for the new import.
+                err.multipart_suggestion(
+                    msg,
+                    vec![
+                        (root_span.shrink_to_lo(), format!("{path};\n{indentation}use ")),
+                        (root_span, replacement),
+                    ],
+                    Applicability::MachineApplicable,
+                );
+                break;
+            }
         }
 
         err.emit();

compiler/rustc_resolve/src/ident.rs

@@ -1362,10 +1362,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     ident,
                     decl: binding,
                     dedup_span: path_span,
+                    root_span,
                     outermost_res: None,
                     source: None,
                     parent_scope: *parent_scope,
-                    single_nested: path_span != root_span,
                 });
             } else {
                 return Err(ControlFlow::Break(Determined));

compiler/rustc_resolve/src/lib.rs

@@ -1031,10 +1031,9 @@ struct PrivacyError<'ra> {
     ident: Ident,
     decl: Decl<'ra>,
     dedup_span: Span,
+    root_span: Span,
     outermost_res: Option<(Res, Ident)>,
     parent_scope: ParentScope<'ra>,
-    /// Is the format `use a::{b,c}`?
-    single_nested: bool,
     source: Option<ast::Expr>,
 }
 

tests/ui/imports/private-import-grouped-suggestion-157453.rs

@@ -0,0 +1,32 @@
+mod one {
+    pub struct One();
+}
+
+mod two {
+    use crate::one::One;
+    pub struct Two();
+}
+
+mod test_grouped {
+    use crate::two::{One, Two}; //~ ERROR struct import `One` is private [E0603]
+}
+
+mod test_single_item {
+    use crate::two::{One}; //~ ERROR struct import `One` is private [E0603]
+}
+
+mod outer {
+    pub mod inner {
+        pub struct MyPath;
+    }
+}
+
+mod reexport {
+    use crate::outer::inner::MyPath;
+}
+
+mod test_std_style {
+    use crate::reexport::{MyPath}; //~ ERROR struct import `MyPath` is private [E0603]
+}
+
+fn main() {}

tests/ui/imports/private-import-grouped-suggestion-157453.stderr

@@ -0,0 +1,69 @@
+error[E0603]: struct import `One` is private
+  --> $DIR/private-import-grouped-suggestion-157453.rs:11:22
+   |
+LL |     use crate::two::{One, Two};
+   |                      ^^^ private struct import
+   |
+note: the struct import `One` is defined here...
+  --> $DIR/private-import-grouped-suggestion-157453.rs:6:9
+   |
+LL |     use crate::one::One;
+   |         ^^^^^^^^^^^^^^^
+note: ...and refers to the struct `One` which is defined here
+  --> $DIR/private-import-grouped-suggestion-157453.rs:2:5
+   |
+LL |     pub struct One();
+   |     ^^^^^^^^^^^^^^^^^ you could import this directly
+help: import `One` directly
+   |
+LL ~     use crate::one::One;
+LL ~     use crate::two::Two;
+   |
+
+error[E0603]: struct import `One` is private
+  --> $DIR/private-import-grouped-suggestion-157453.rs:15:22
+   |
+LL |     use crate::two::{One};
+   |                      ^^^ private struct import
+   |
+note: the struct import `One` is defined here...
+  --> $DIR/private-import-grouped-suggestion-157453.rs:6:9
+   |
+LL |     use crate::one::One;
+   |         ^^^^^^^^^^^^^^^
+note: ...and refers to the struct `One` which is defined here
+  --> $DIR/private-import-grouped-suggestion-157453.rs:2:5
+   |
+LL |     pub struct One();
+   |     ^^^^^^^^^^^^^^^^^ you could import this directly
+help: import `One` directly
+   |
+LL -     use crate::two::{One};
+LL +     use crate::one::One;
+   |
+
+error[E0603]: struct import `MyPath` is private
+  --> $DIR/private-import-grouped-suggestion-157453.rs:29:27
+   |
+LL |     use crate::reexport::{MyPath};
+   |                           ^^^^^^ private struct import
+   |
+note: the struct import `MyPath` is defined here...
+  --> $DIR/private-import-grouped-suggestion-157453.rs:25:9
+   |
+LL |     use crate::outer::inner::MyPath;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: ...and refers to the struct `MyPath` which is defined here
+  --> $DIR/private-import-grouped-suggestion-157453.rs:20:9
+   |
+LL |         pub struct MyPath;
+   |         ^^^^^^^^^^^^^^^^^^ you could import this directly
+help: import `MyPath` directly
+   |
+LL -     use crate::reexport::{MyPath};
+LL +     use crate::outer::inner::MyPath;
+   |
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0603`.

tests/ui/imports/private-import-nested-suggestion-156060.stderr

@@ -14,6 +14,11 @@ note: ...and refers to the struct `One` which is defined here
    |
 LL |     pub struct One();
    |     ^^^^^^^^^^^^^^^^^ you could import this directly
+help: import `One` directly
+   |
+LL ~     use crate::one::One;
+LL ~     use crate::two::Two;
+   |
 
 error: aborting due to 1 previous error
 

tests/ui/imports/private-import-suggestion-path-156244.edition_2015.stderr

@@ -36,6 +36,11 @@ note: ...and refers to the struct `One` which is defined here
    |
 LL |     pub struct One;
    |     ^^^^^^^^^^^^^^^ you could import this directly
+help: import `One` directly
+   |
+LL ~     use crate::a::One;
+LL ~     use crate::b::Two;
+   |
 
 error[E0603]: struct import `Two` is private
   --> $DIR/private-import-suggestion-path-156244.rs:35:25
@@ -53,6 +58,11 @@ note: ...and refers to the struct `Two` which is defined here
    |
 LL |     pub struct Two;
    |     ^^^^^^^^^^^^^^^ you could import this directly
+help: import `Two` directly
+   |
+LL ~     use crate::a::Two;
+LL ~     use crate::b::One;
+   |
 
 error[E0603]: module import `inner` is private
   --> $DIR/private-import-suggestion-path-156244.rs:38:24

tests/ui/imports/private-import-suggestion-path-156244.edition_2018.stderr

@@ -36,6 +36,11 @@ note: ...and refers to the struct `One` which is defined here
    |
 LL |     pub struct One;
    |     ^^^^^^^^^^^^^^^ you could import this directly
+help: import `One` directly
+   |
+LL ~     use crate::a::One;
+LL ~     use crate::b::Two;
+   |
 
 error[E0603]: struct import `Two` is private
   --> $DIR/private-import-suggestion-path-156244.rs:35:25
@@ -53,6 +58,11 @@ note: ...and refers to the struct `Two` which is defined here
    |
 LL |     pub struct Two;
    |     ^^^^^^^^^^^^^^^ you could import this directly
+help: import `Two` directly
+   |
+LL ~     use crate::a::Two;
+LL ~     use crate::b::One;
+   |
 
 error[E0603]: module import `inner` is private
   --> $DIR/private-import-suggestion-path-156244.rs:38:24