Allow qualified paths in struct construction (both expressions and patterns)

compiler/rustc_ast/src/ast.rs

@@ -623,12 +623,13 @@ impl Pat {
             PatKind::Ident(_, _, Some(p)) => p.walk(it),
 
             // Walk into each field of struct.
-            PatKind::Struct(_, fields, _) => fields.iter().for_each(|field| field.pat.walk(it)),
+            PatKind::Struct(_, _, fields, _) => fields.iter().for_each(|field| field.pat.walk(it)),
 
             // Sequence of patterns.
-            PatKind::TupleStruct(_, s) | PatKind::Tuple(s) | PatKind::Slice(s) | PatKind::Or(s) => {
-                s.iter().for_each(|p| p.walk(it))
-            }
+            PatKind::TupleStruct(_, _, s)
+            | PatKind::Tuple(s)
+            | PatKind::Slice(s)
+            | PatKind::Or(s) => s.iter().for_each(|p| p.walk(it)),
 
             // Trivial wrappers over inner patterns.
             PatKind::Box(s) | PatKind::Ref(s, _) | PatKind::Paren(s) => s.walk(it),
@@ -701,10 +702,10 @@ pub enum PatKind {
 
     /// A struct or struct variant pattern (e.g., `Variant {x, y, ..}`).
     /// The `bool` is `true` in the presence of a `..`.
-    Struct(Path, Vec<PatField>, /* recovered */ bool),
+    Struct(Option<QSelf>, Path, Vec<PatField>, /* recovered */ bool),
 
     /// A tuple struct/variant pattern (`Variant(x, y, .., z)`).
-    TupleStruct(Path, Vec<P<Pat>>),
+    TupleStruct(Option<QSelf>, Path, Vec<P<Pat>>),
 
     /// An or-pattern `A | B | C`.
     /// Invariant: `pats.len() >= 2`.
@@ -1247,6 +1248,7 @@ pub enum StructRest {
 
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct StructExpr {
+    pub qself: Option<QSelf>,
     pub path: Path,
     pub fields: Vec<ExprField>,
     pub rest: StructRest,

compiler/rustc_ast/src/mut_visit.rs

@@ -1139,15 +1139,17 @@ pub fn noop_visit_pat<T: MutVisitor>(pat: &mut P<Pat>, vis: &mut T) {
             visit_opt(sub, |sub| vis.visit_pat(sub));
         }
         PatKind::Lit(e) => vis.visit_expr(e),
-        PatKind::TupleStruct(path, elems) => {
+        PatKind::TupleStruct(qself, path, elems) => {
+            vis.visit_qself(qself);
             vis.visit_path(path);
             visit_vec(elems, |elem| vis.visit_pat(elem));
         }
         PatKind::Path(qself, path) => {
             vis.visit_qself(qself);
             vis.visit_path(path);
         }
-        PatKind::Struct(path, fields, _etc) => {
+        PatKind::Struct(qself, path, fields, _etc) => {
+            vis.visit_qself(qself);
             vis.visit_path(path);
             fields.flat_map_in_place(|field| vis.flat_map_pat_field(field));
         }
@@ -1333,7 +1335,8 @@ pub fn noop_visit_expr<T: MutVisitor>(
         }
         ExprKind::MacCall(mac) => vis.visit_mac_call(mac),
         ExprKind::Struct(se) => {
-            let StructExpr { path, fields, rest } = se.deref_mut();
+            let StructExpr { qself, path, fields, rest } = se.deref_mut();
+            vis.visit_qself(qself);
             vis.visit_path(path);
             fields.flat_map_in_place(|field| vis.flat_map_expr_field(field));
             match rest {

compiler/rustc_ast/src/visit.rs

@@ -497,7 +497,10 @@ pub fn walk_assoc_ty_constraint<'a, V: Visitor<'a>>(
 
 pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
     match pattern.kind {
-        PatKind::TupleStruct(ref path, ref elems) => {
+        PatKind::TupleStruct(ref opt_qself, ref path, ref elems) => {
+            if let Some(ref qself) = *opt_qself {
+                visitor.visit_ty(&qself.ty);
+            }
             visitor.visit_path(path, pattern.id);
             walk_list!(visitor, visit_pat, elems);
         }
@@ -507,7 +510,10 @@ pub fn walk_pat<'a, V: Visitor<'a>>(visitor: &mut V, pattern: &'a Pat) {
             }
             visitor.visit_path(path, pattern.id)
         }
-        PatKind::Struct(ref path, ref fields, _) => {
+        PatKind::Struct(ref opt_qself, ref path, ref fields, _) => {
+            if let Some(ref qself) = *opt_qself {
+                visitor.visit_ty(&qself.ty);
+            }
             visitor.visit_path(path, pattern.id);
             walk_list!(visitor, visit_pat_field, fields);
         }
@@ -740,6 +746,9 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             visitor.visit_anon_const(count)
         }
         ExprKind::Struct(ref se) => {
+            if let Some(ref qself) = se.qself {
+                visitor.visit_ty(&qself.ty);
+            }
             visitor.visit_path(&se.path, expression.id);
             walk_list!(visitor, visit_expr_field, &se.fields);
             match &se.rest {

compiler/rustc_ast_lowering/src/expr.rs

@@ -237,7 +237,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     hir::ExprKind::Struct(
                         self.arena.alloc(self.lower_qpath(
                             e.id,
-                            &None,
+                            &se.qself,
                             &se.path,
                             ParamMode::Optional,
                             ImplTraitContext::disallowed(),
@@ -1041,18 +1041,20 @@ impl<'hir> LoweringContext<'_, 'hir> {
     /// It is not a complete check, but just tries to reject most paths early
     /// if they are not tuple structs.
     /// Type checking will take care of the full validation later.
-    fn extract_tuple_struct_path<'a>(&mut self, expr: &'a Expr) -> Option<&'a Path> {
-        // For tuple struct destructuring, it must be a non-qualified path (like in patterns).
-        if let ExprKind::Path(None, path) = &expr.kind {
-            // Does the path resolves to something disallowed in a tuple struct/variant pattern?
+    fn extract_tuple_struct_path<'a>(
+        &mut self,
+        expr: &'a Expr,
+    ) -> Option<(&'a Option<QSelf>, &'a Path)> {
+        if let ExprKind::Path(qself, path) = &expr.kind {
+            // Does the path resolve to something disallowed in a tuple struct/variant pattern?
             if let Some(partial_res) = self.resolver.get_partial_res(expr.id) {
                 if partial_res.unresolved_segments() == 0
                     && !partial_res.base_res().expected_in_tuple_struct_pat()
                 {
                     return None;
                 }
             }
-            return Some(path);
+            return Some((qself, path));
         }
         None
     }
@@ -1088,7 +1090,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
             }
             // Tuple structs.
             ExprKind::Call(callee, args) => {
-                if let Some(path) = self.extract_tuple_struct_path(callee) {
+                if let Some((qself, path)) = self.extract_tuple_struct_path(callee) {
                     let (pats, rest) = self.destructure_sequence(
                         args,
                         "tuple struct or variant",
@@ -1097,7 +1099,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     );
                     let qpath = self.lower_qpath(
                         callee.id,
-                        &None,
+                        qself,
                         path,
                         ParamMode::Optional,
                         ImplTraitContext::disallowed(),
@@ -1122,7 +1124,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 }));
                 let qpath = self.lower_qpath(
                     lhs.id,
-                    &None,
+                    &se.qself,
                     &se.path,
                     ParamMode::Optional,
                     ImplTraitContext::disallowed(),

compiler/rustc_ast_lowering/src/pat.rs

@@ -21,10 +21,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         break self.lower_pat_ident(pattern, binding_mode, ident, lower_sub);
                     }
                     PatKind::Lit(ref e) => break hir::PatKind::Lit(self.lower_expr(e)),
-                    PatKind::TupleStruct(ref path, ref pats) => {
+                    PatKind::TupleStruct(ref qself, ref path, ref pats) => {
                         let qpath = self.lower_qpath(
                             pattern.id,
-                            &None,
+                            qself,
                             path,
                             ParamMode::Optional,
                             ImplTraitContext::disallowed(),
@@ -47,10 +47,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         );
                         break hir::PatKind::Path(qpath);
                     }
-                    PatKind::Struct(ref path, ref fields, etc) => {
+                    PatKind::Struct(ref qself, ref path, ref fields, etc) => {
                         let qpath = self.lower_qpath(
                             pattern.id,
-                            &None,
+                            qself,
                             path,
                             ParamMode::Optional,
                             ImplTraitContext::disallowed(),

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -705,6 +705,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
         "async closures are unstable",
         "to use an async block, remove the `||`: `async {`"
     );
+    gate_all!(more_qualified_paths, "usage of qualified paths in this context is experimental");
     gate_all!(generators, "yield syntax is experimental");
     gate_all!(raw_ref_op, "raw address of syntax is experimental");
     gate_all!(const_trait_bound_opt_out, "`?const` on trait bounds is experimental");

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1713,11 +1713,16 @@ impl<'a> State<'a> {
 
     fn print_expr_struct(
         &mut self,
+        qself: &Option<ast::QSelf>,
         path: &ast::Path,
         fields: &[ast::ExprField],
         rest: &ast::StructRest,
     ) {
-        self.print_path(path, true, 0);
+        if let Some(qself) = qself {
+            self.print_qpath(path, qself, true);
+        } else {
+            self.print_path(path, true, 0);
+        }
         self.s.word("{");
         self.commasep_cmnt(
             Consistent,
@@ -1874,7 +1879,7 @@ impl<'a> State<'a> {
                 self.print_expr_repeat(element, count);
             }
             ast::ExprKind::Struct(ref se) => {
-                self.print_expr_struct(&se.path, &se.fields, &se.rest);
+                self.print_expr_struct(&se.qself, &se.path, &se.fields, &se.rest);
             }
             ast::ExprKind::Tup(ref exprs) => {
                 self.print_expr_tup(exprs);
@@ -2340,8 +2345,12 @@ impl<'a> State<'a> {
                     self.print_pat(p);
                 }
             }
-            PatKind::TupleStruct(ref path, ref elts) => {
-                self.print_path(path, true, 0);
+            PatKind::TupleStruct(ref qself, ref path, ref elts) => {
+                if let Some(qself) = qself {
+                    self.print_qpath(path, qself, true);
+                } else {
+                    self.print_path(path, true, 0);
+                }
                 self.popen();
                 self.commasep(Inconsistent, &elts[..], |s, p| s.print_pat(p));
                 self.pclose();
@@ -2355,8 +2364,12 @@ impl<'a> State<'a> {
             PatKind::Path(Some(ref qself), ref path) => {
                 self.print_qpath(path, qself, false);
             }
-            PatKind::Struct(ref path, ref fields, etc) => {
-                self.print_path(path, true, 0);
+            PatKind::Struct(ref qself, ref path, ref fields, etc) => {
+                if let Some(qself) = qself {
+                    self.print_qpath(path, qself, true);
+                } else {
+                    self.print_path(path, true, 0);
+                }
                 self.nbsp();
                 self.word_space("{");
                 self.commasep_cmnt(

compiler/rustc_expand/src/build.rs

@@ -275,7 +275,12 @@ impl<'a> ExtCtxt<'a> {
     ) -> P<ast::Expr> {
         self.expr(
             span,
-            ast::ExprKind::Struct(P(ast::StructExpr { path, fields, rest: ast::StructRest::None })),
+            ast::ExprKind::Struct(P(ast::StructExpr {
+                qself: None,
+                path,
+                fields,
+                rest: ast::StructRest::None,
+            })),
         )
     }
     pub fn expr_struct_ident(
@@ -405,15 +410,15 @@ impl<'a> ExtCtxt<'a> {
         path: ast::Path,
         subpats: Vec<P<ast::Pat>>,
     ) -> P<ast::Pat> {
-        self.pat(span, PatKind::TupleStruct(path, subpats))
+        self.pat(span, PatKind::TupleStruct(None, path, subpats))
     }
     pub fn pat_struct(
         &self,
         span: Span,
         path: ast::Path,
         field_pats: Vec<ast::PatField>,
     ) -> P<ast::Pat> {
-        self.pat(span, PatKind::Struct(path, field_pats, false))
+        self.pat(span, PatKind::Struct(None, path, field_pats, false))
     }
     pub fn pat_tuple(&self, span: Span, pats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
         self.pat(span, PatKind::Tuple(pats))

compiler/rustc_feature/src/active.rs

@@ -663,6 +663,9 @@ declare_features! (
     /// Allows unnamed fields of struct and union type
     (active, unnamed_fields, "1.53.0", Some(49804), None),
 
+    /// Allows qualified paths in struct expressions, struct patterns and tuple struct patterns.
+    (active, more_qualified_paths, "1.54.0", Some(80080), None),
+
     // -------------------------------------------------------------------------
     // feature-group-end: actual feature gates
     // -------------------------------------------------------------------------

compiler/rustc_lint/src/unused.rs

@@ -858,10 +858,10 @@ impl EarlyLintPass for UnusedParens {
             // The other cases do not contain sub-patterns.
             | Wild | Rest | Lit(..) | MacCall(..) | Range(..) | Ident(.., None) | Path(..) => {},
             // These are list-like patterns; parens can always be removed.
-            TupleStruct(_, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps {
+            TupleStruct(_, _, ps) | Tuple(ps) | Slice(ps) | Or(ps) => for p in ps {
                 self.check_unused_parens_pat(cx, p, false, false);
             },
-            Struct(_, fps, _) => for f in fps {
+            Struct(_, _, fps, _) => for f in fps {
                 self.check_unused_parens_pat(cx, &f.pat, false, false);
             },
             // Avoid linting on `i @ (p0 | .. | pn)` and `box (p0 | .. | pn)`, #64106.

compiler/rustc_parse/src/parser/attr.rs

@@ -32,7 +32,6 @@ impl<'a> Parser<'a> {
         let mut just_parsed_doc_comment = false;
         let start_pos = self.token_cursor.num_next_calls;
         loop {
-            debug!("parse_outer_attributes: self.token={:?}", self.token);
             let attr = if self.check(&token::Pound) {
                 let inner_error_reason = if just_parsed_doc_comment {
                     "an inner attribute is not permitted following an outer doc comment"

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -366,7 +366,7 @@ impl<'a> Parser<'a> {
             let mut snapshot = self.clone();
             let path =
                 Path { segments: vec![], span: self.prev_token.span.shrink_to_lo(), tokens: None };
-            let struct_expr = snapshot.parse_struct_expr(path, AttrVec::new(), false);
+            let struct_expr = snapshot.parse_struct_expr(None, path, AttrVec::new(), false);
             let block_tail = self.parse_block_tail(lo, s, AttemptLocalParseRecovery::No);
             return Some(match (struct_expr, block_tail) {
                 (Ok(expr), Err(mut err)) => {