Unrolled build for #155137

Rollup merge of #155137 - mu001999-contrib:self-at-end, r=petrochenkov

Allow trailing `self` in more contexts

Reference PR:

- rust-lang/reference#2237

As a follow-up PR to #152996, after this PR:
1. Trailing `self` can appear in paths
2. [E0429](https://doc.rust-lang.org/stable/error_codes/E0429.html#error-code-e0429) will be no longer emitted, `use ...::self [as target];` will be equivalent to `use ...::{self [as target]};`

r? petrochenkov

Author: rust-timer

compiler/rustc_error_codes/src/error_codes/E0429.md

@@ -1,9 +1,11 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 The `self` keyword cannot appear alone as the last segment in a `use`
 declaration.
 
 Erroneous code example:
 
-```compile_fail,E0429
+```ignore (error is no longer emitted)
 use std::fmt::self; // error: `self` imports are only allowed within a { } list
 ```
 

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -37,7 +37,7 @@ use crate::ref_mut::CmCell;
 use crate::{
     BindingKey, Decl, DeclData, DeclKind, ExternModule, ExternPreludeEntry, Finalize, IdentKey,
     LocalModule, MacroData, Module, ModuleKind, ModuleOrUniformRoot, ParentScope, PathResult, Res,
-    ResolutionError, Resolver, Segment, Used, VisResolutionError, errors,
+    Resolver, Segment, Used, VisResolutionError, errors,
 };
 
 impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
@@ -531,18 +531,16 @@ impl<'a, 'ra, 'tcx> DefCollector<'a, 'ra, 'tcx> {
 
         self.r.indeterminate_imports.push(import);
         match import.kind {
-            ImportKind::Single { target, type_ns_only, .. } => {
+            ImportKind::Single { target, .. } => {
                 // Don't add underscore imports to `single_imports`
                 // because they cannot define any usable names.
                 if target.name != kw::Underscore {
                     self.r.per_ns(|this, ns| {
-                        if !type_ns_only || ns == TypeNS {
-                            let key = BindingKey::new(IdentKey::new(target), ns);
-                            this.resolution_or_default(current_module, key, target.span)
-                                .borrow_mut(this)
-                                .single_imports
-                                .insert(import);
-                        }
+                        let key = BindingKey::new(IdentKey::new(target), ns);
+                        this.resolution_or_default(current_module, key, target.span)
+                            .borrow_mut(this)
+                            .single_imports
+                            .insert(import);
                     });
                 }
             }
@@ -612,30 +610,8 @@ impl<'a, 'ra, 'tcx> DefCollector<'a, 'ra, 'tcx> {
                 let mut module_path = prefix;
                 let source = module_path.pop().unwrap();
 
-                // `true` for `...::{self [as target]}` imports, `false` otherwise.
-                let type_ns_only = nested && source.ident.name == kw::SelfLower;
-
-                // Suggest `use prefix::{self};` for `use prefix::self;`
-                if source.ident.name == kw::SelfLower
-                    && let Some(parent) = module_path.last()
-                    && !type_ns_only
-                    && (parent.ident.name != kw::PathRoot
-                        || self.r.path_root_is_crate_root(parent.ident))
-                {
-                    let span_with_rename = match rename {
-                        Some(rename) => source.ident.span.to(rename.span),
-                        None => source.ident.span,
-                    };
-
-                    self.r.report_error(
-                        parent.ident.span.shrink_to_hi().to(source.ident.span),
-                        ResolutionError::SelfImportsOnlyAllowedWithin {
-                            root: parent.ident.name == kw::PathRoot,
-                            span_with_rename,
-                        },
-                    );
-                }
-
+                // If the identifier is `self` without a rename,
+                // then it is replaced with the parent identifier.
                 let ident = if source.ident.name == kw::SelfLower
                     && rename.is_none()
                     && let Some(parent) = module_path.last()
@@ -689,30 +665,36 @@ impl<'a, 'ra, 'tcx> DefCollector<'a, 'ra, 'tcx> {
                         self.r.dcx().span_err(use_tree.span(), "extern prelude cannot be imported");
                         return;
                     }
-                    _ => {}
+                    _ => (),
+                }
+
+                // Deny `use ...::self::source [as target];` or `use ...::self::self [as target];`,
+                // but allow `use self::source [as target];` and `use self::self as target;`.
+                if let Some(parent) = module_path.last()
+                    && parent.ident.name == kw::SelfLower
+                    && module_path.len() > 1
+                {
+                    self.r.dcx().span_err(
+                        parent.ident.span,
+                        "`self` in paths can only be used in start position or last position",
+                    );
+                    return;
                 }
 
                 // Deny importing path-kw without renaming
                 if rename.is_none() && ident.is_path_segment_keyword() {
                     let ident = use_tree.ident();
-
-                    // Don't suggest `use xx::self as name;` for `use xx::self;`
-                    // But it's OK to suggest `use xx::{self as name};` for `use xx::{self};`
-                    let sugg = if !type_ns_only && ident.name == kw::SelfLower {
-                        None
-                    } else {
-                        Some(errors::UnnamedImportSugg { span: ident.span, ident })
-                    };
-
-                    self.r.dcx().emit_err(errors::UnnamedImport { span: ident.span, sugg });
+                    self.r.dcx().emit_err(errors::UnnamedImport {
+                        span: ident.span,
+                        sugg: errors::UnnamedImportSugg { span: ident.span, ident },
+                    });
                     return;
                 }
 
                 let kind = ImportKind::Single {
                     source: source.ident,
                     target: ident,
                     decls: Default::default(),
-                    type_ns_only,
                     nested,
                     id,
                 };

compiler/rustc_resolve/src/diagnostics.rs

@@ -386,9 +386,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         let mut suggestion = None;
         let mut span = binding_span;
         match import.kind {
-            ImportKind::Single { type_ns_only: true, .. } => {
-                suggestion = Some(format!("self as {suggested_name}"))
-            }
             ImportKind::Single { source, .. } => {
                 if let Some(pos) = source.span.hi().0.checked_sub(binding_span.lo().0)
                     && let Ok(snippet) = self.tcx.sess.source_map().span_to_snippet(binding_span)
@@ -913,29 +910,6 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     sub_unreachable,
                 })
             }
-            ResolutionError::SelfImportsOnlyAllowedWithin { root, span_with_rename } => {
-                // None of the suggestions below would help with a case like `use self`.
-                let (suggestion, mpart_suggestion) = if root {
-                    (None, None)
-                } else {
-                    // use foo::bar::self        -> foo::bar
-                    // use foo::bar::self as abc -> foo::bar as abc
-                    let suggestion = errs::SelfImportsOnlyAllowedWithinSuggestion { span };
-
-                    // use foo::bar::self        -> foo::bar::{self}
-                    // use foo::bar::self as abc -> foo::bar::{self as abc}
-                    let mpart_suggestion = errs::SelfImportsOnlyAllowedWithinMultipartSuggestion {
-                        multipart_start: span_with_rename.shrink_to_lo(),
-                        multipart_end: span_with_rename.shrink_to_hi(),
-                    };
-                    (Some(suggestion), Some(mpart_suggestion))
-                };
-                self.dcx().create_err(errs::SelfImportsOnlyAllowedWithin {
-                    span,
-                    suggestion,
-                    mpart_suggestion,
-                })
-            }
             ResolutionError::FailedToResolve { segment, label, suggestion, module, message } => {
                 let mut err = struct_span_code_err!(self.dcx(), span, E0433, "{message}");
                 err.span_label(span, label);

compiler/rustc_resolve/src/errors.rs

@@ -301,40 +301,6 @@ pub(crate) struct AttemptToUseNonConstantValueInConstantWithoutSuggestion<'a> {
     pub(crate) suggestion: &'a str,
 }
 
-#[derive(Diagnostic)]
-#[diag("`self` imports are only allowed within a {\"{\"} {\"}\"} list", code = E0429)]
-pub(crate) struct SelfImportsOnlyAllowedWithin {
-    #[primary_span]
-    pub(crate) span: Span,
-    #[subdiagnostic]
-    pub(crate) suggestion: Option<SelfImportsOnlyAllowedWithinSuggestion>,
-    #[subdiagnostic]
-    pub(crate) mpart_suggestion: Option<SelfImportsOnlyAllowedWithinMultipartSuggestion>,
-}
-
-#[derive(Subdiagnostic)]
-#[suggestion(
-    "consider importing the module directly",
-    code = "",
-    applicability = "machine-applicable"
-)]
-pub(crate) struct SelfImportsOnlyAllowedWithinSuggestion {
-    #[primary_span]
-    pub(crate) span: Span,
-}
-
-#[derive(Subdiagnostic)]
-#[multipart_suggestion(
-    "alternatively, use the multi-path `use` syntax to import `self`",
-    applicability = "machine-applicable"
-)]
-pub(crate) struct SelfImportsOnlyAllowedWithinMultipartSuggestion {
-    #[suggestion_part(code = "{{")]
-    pub(crate) multipart_start: Span,
-    #[suggestion_part(code = "}}")]
-    pub(crate) multipart_end: Span,
-}
-
 #[derive(Diagnostic)]
 #[diag("{$shadowing_binding}s cannot shadow {$shadowed_binding}s", code = E0530)]
 pub(crate) struct BindingShadowsSomethingUnacceptable<'a> {
@@ -998,7 +964,7 @@ pub(crate) struct UnnamedImport {
     #[primary_span]
     pub(crate) span: Span,
     #[subdiagnostic]
-    pub(crate) sugg: Option<UnnamedImportSugg>,
+    pub(crate) sugg: UnnamedImportSugg,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_resolve/src/ident.rs

@@ -1837,8 +1837,10 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 }
             }
 
+            let allow_trailing_self = is_last && name == kw::SelfLower;
+
             // Report special messages for path segment keywords in wrong positions.
-            if ident.is_path_segment_keyword() && segment_idx != 0 {
+            if ident.is_path_segment_keyword() && segment_idx != 0 && !allow_trailing_self {
                 return PathResult::failed(
                     ident,
                     false,
@@ -1858,6 +1860,14 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                                 format!("global paths cannot start with {name_str}"),
                                 "cannot start with this".to_string(),
                             )
+                        } else if name == kw::SelfLower {
+                            (
+                                format!(
+                                    "`self` in paths can only be used in start position or last position"
+                                ),
+                                "can only be used in path start position or last position"
+                                    .to_string(),
+                            )
                         } else {
                             (
                                 format!("{name_str} in paths can only be used in start position"),