Implement RFC 2302: tuple_struct_self_ctor

src/doc/unstable-book/src/language-features/self-struct-ctor.md

@@ -0,0 +1,33 @@
+# `self_struct_ctor`
+
+The tracking issue for this feature is: [#51994]
+[#51994]: https://github.com/rust-lang/rust/issues/51994
+
+------------------------
+
+The `self_struct_ctor` feature gate lets you use the special `Self`
+identifier as a constructor and a pattern.
+
+A simple example is:
+
+```rust
+#![feature(self_struct_ctor)]
+
+struct ST(i32, i32);
+
+impl ST {
+    fn new() -> Self {
+        ST(0, 1)
+    }
+
+    fn ctor() -> Self {
+        Self(1,2)           // constructed by `Self`, it is the same as `ST(1, 2)`
+    }
+
+    fn pattern(self) {
+        match self {
+            Self(x, y) => println!("{} {}", x, y), // used as a pattern
+        }
+    }
+}
+```

src/librustc/hir/def.rs

@@ -69,6 +69,7 @@ pub enum Def {
     Static(DefId, bool /* is_mutbl */),
     StructCtor(DefId, CtorKind), // DefId refers to NodeId of the struct's constructor
     VariantCtor(DefId, CtorKind), // DefId refers to the enum variant
+    SelfCtor(DefId /* impl */),  // DefId refers to the impl
     Method(DefId),
     AssociatedConst(DefId),
 
@@ -272,7 +273,8 @@ impl Def {
             Def::AssociatedTy(id) | Def::TyParam(id) | Def::Struct(id) | Def::StructCtor(id, ..) |
             Def::Union(id) | Def::Trait(id) | Def::Method(id) | Def::Const(id) |
             Def::AssociatedConst(id) | Def::Macro(id, ..) |
-            Def::Existential(id) | Def::AssociatedExistential(id) | Def::ForeignTy(id) => {
+            Def::Existential(id) | Def::AssociatedExistential(id) | Def::ForeignTy(id) |
+            Def::SelfCtor(id) => {
                 id
             }
 
@@ -309,6 +311,7 @@ impl Def {
             Def::StructCtor(.., CtorKind::Fn) => "tuple struct",
             Def::StructCtor(.., CtorKind::Const) => "unit struct",
             Def::StructCtor(.., CtorKind::Fictive) => bug!("impossible struct constructor"),
+            Def::SelfCtor(..) => "self constructor",
             Def::Union(..) => "union",
             Def::Trait(..) => "trait",
             Def::ForeignTy(..) => "foreign type",

src/librustc/hir/lowering.rs

@@ -67,6 +67,7 @@ use syntax::ast;
 use syntax::ast::*;
 use syntax::errors;
 use syntax::ext::hygiene::{Mark, SyntaxContext};
+use syntax::feature_gate::{emit_feature_err, GateIssue};
 use syntax::print::pprust;
 use syntax::ptr::P;
 use syntax::source_map::{self, respan, CompilerDesugaringKind, Spanned};
@@ -3429,19 +3430,24 @@ impl<'a> LoweringContext<'a> {
                     ParamMode::Optional,
                     ImplTraitContext::Disallowed,
                 );
+                self.check_self_struct_ctor_feature(&qpath);
                 hir::PatKind::TupleStruct(
                     qpath,
                     pats.iter().map(|x| self.lower_pat(x)).collect(),
                     ddpos,
                 )
             }
-            PatKind::Path(ref qself, ref path) => hir::PatKind::Path(self.lower_qpath(
-                p.id,
-                qself,
-                path,
-                ParamMode::Optional,
-                ImplTraitContext::Disallowed,
-            )),
+            PatKind::Path(ref qself, ref path) => {
+                let qpath = self.lower_qpath(
+                    p.id,
+                    qself,
+                    path,
+                    ParamMode::Optional,
+                    ImplTraitContext::Disallowed,
+                );
+                self.check_self_struct_ctor_feature(&qpath);
+                hir::PatKind::Path(qpath)
+            }
             PatKind::Struct(ref path, ref fields, etc) => {
                 let qpath = self.lower_qpath(
                     p.id,
@@ -3828,13 +3834,17 @@ impl<'a> LoweringContext<'a> {
                     attrs: e.attrs.clone(),
                 };
             }
-            ExprKind::Path(ref qself, ref path) => hir::ExprKind::Path(self.lower_qpath(
-                e.id,
-                qself,
-                path,
-                ParamMode::Optional,
-                ImplTraitContext::Disallowed,
-            )),
+            ExprKind::Path(ref qself, ref path) => {
+                let qpath = self.lower_qpath(
+                    e.id,
+                    qself,
+                    path,
+                    ParamMode::Optional,
+                    ImplTraitContext::Disallowed,
+                );
+                self.check_self_struct_ctor_feature(&qpath);
+                hir::ExprKind::Path(qpath)
+            }
             ExprKind::Break(opt_label, ref opt_expr) => {
                 let destination = if self.is_in_loop_condition && opt_label.is_none() {
                     hir::Destination {
@@ -4815,6 +4825,18 @@ impl<'a> LoweringContext<'a> {
                                             ThinVec::new()));
         P(self.expr_call(e.span, from_err, hir_vec![e]))
     }
+
+    fn check_self_struct_ctor_feature(&self, qp: &hir::QPath) {
+        if let hir::QPath::Resolved(_, ref p) = qp {
+            if p.segments.len() == 1 &&
+               p.segments[0].ident.name == keywords::SelfType.name() &&
+               !self.sess.features_untracked().self_struct_ctor {
+                emit_feature_err(&self.sess.parse_sess, "self_struct_ctor",
+                                 p.span, GateIssue::Language,
+                                 "`Self` struct constructors are unstable");
+            }
+        }
+    }
 }
 
 fn body_ids(bodies: &BTreeMap<hir::BodyId, hir::Body>) -> Vec<hir::BodyId> {

src/librustc/ich/impls_hir.rs

@@ -1021,6 +1021,7 @@ impl_stable_hash_for!(enum hir::def::Def {
     Const(def_id),
     Static(def_id, is_mutbl),
     StructCtor(def_id, ctor_kind),
+    SelfCtor(impl_def_id),
     VariantCtor(def_id, ctor_kind),
     Method(def_id),
     AssociatedConst(def_id),

src/librustc/middle/mem_categorization.rs

@@ -708,7 +708,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
 
         match def {
           Def::StructCtor(..) | Def::VariantCtor(..) | Def::Const(..) |
-          Def::AssociatedConst(..) | Def::Fn(..) | Def::Method(..) => {
+          Def::AssociatedConst(..) | Def::Fn(..) | Def::Method(..) | Def::SelfCtor(..) => {
                 Ok(self.cat_rvalue_node(hir_id, span, expr_ty))
           }
 
@@ -1288,7 +1288,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
                     (self.cat_downcast_if_needed(pat, cmt, def_id),
                      self.tcx.adt_def(enum_def).variant_with_id(def_id).fields.len())
                 }
-                Def::StructCtor(_, CtorKind::Fn) => {
+                Def::StructCtor(_, CtorKind::Fn) | Def::SelfCtor(..) => {
                     match self.pat_ty_unadjusted(&pat)?.sty {
                         ty::Adt(adt_def, _) => {
                             (cmt, adt_def.non_enum_variant().fields.len())

src/librustc/middle/stability.rs

@@ -783,7 +783,7 @@ impl<'a, 'tcx> Visitor<'tcx> for Checker<'a, 'tcx> {
     fn visit_path(&mut self, path: &'tcx hir::Path, id: hir::HirId) {
         let id = self.tcx.hir.hir_to_node_id(id);
         match path.def {
-            Def::Local(..) | Def::Upvar(..) |
+            Def::Local(..) | Def::Upvar(..) | Def::SelfCtor(..) |
             Def::PrimTy(..) | Def::SelfTy(..) | Def::Err => {}
             _ => self.tcx.check_stability(path.def.def_id(), Some(id), path.span)
         }

src/librustc/ty/mod.rs

@@ -2134,7 +2134,8 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         match def {
             Def::Variant(vid) | Def::VariantCtor(vid, ..) => self.variant_with_id(vid),
             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
-            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => self.non_enum_variant(),
+            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) |
+            Def::SelfCtor(..) => self.non_enum_variant(),
             _ => bug!("unexpected def {:?} in variant_of_def", def)
         }
     }

src/librustc_mir/hair/cx/expr.rs

@@ -273,7 +273,8 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                             Def::VariantCtor(variant_id, CtorKind::Fn) => {
                                 Some((adt_def, adt_def.variant_index_with_id(variant_id)))
                             }
-                            Def::StructCtor(_, CtorKind::Fn) => Some((adt_def, 0)),
+                            Def::StructCtor(_, CtorKind::Fn) |
+                            Def::SelfCtor(..) => Some((adt_def, 0)),
                             _ => None,
                         }
                     })
@@ -759,6 +760,25 @@ fn user_annotated_ty_for_def(
                 sty => bug!("unexpected sty: {:?}", sty),
             },
 
+        // `Self` is used in expression as a tuple struct constructor or an unit struct constructor
+        Def::SelfCtor(_) => {
+            let sty = &cx.tables().node_id_to_type(hir_id).sty;
+            match sty {
+                ty::FnDef(ref def_id, _) => {
+                    Some(cx.tables().user_substs(hir_id)?.unchecked_map(|user_substs| {
+                        // Here, we just pair a `DefId` with the
+                        // `user_substs`, so no new types etc are introduced.
+                        cx.tcx().mk_fn_def(*def_id, user_substs)
+                    }))
+                }
+                ty::Adt(ref adt_def, _) => {
+                    user_annotated_ty_for_adt(cx, hir_id, adt_def)
+                }
+                _ => {
+                    bug!("unexpected sty: {:?}", sty)
+                }
+            }
+        }
         _ =>
             bug!("user_annotated_ty_for_def: unexpected def {:?} at {:?}", def, hir_id)
     }
@@ -857,7 +877,8 @@ fn convert_path_expr<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         Def::Fn(_) |
         Def::Method(_) |
         Def::StructCtor(_, CtorKind::Fn) |
-        Def::VariantCtor(_, CtorKind::Fn) => {
+        Def::VariantCtor(_, CtorKind::Fn) |
+        Def::SelfCtor(..) => {
             let user_ty = user_annotated_ty_for_def(cx, expr.hir_id, &def);
             ExprKind::Literal {
                 literal: ty::Const::zero_sized(

src/librustc_mir/hair/pattern/mod.rs

@@ -667,7 +667,7 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
             }
 
             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
-            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
+            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) | Def::SelfCtor(..) => {
                 PatternKind::Leaf { subpatterns: subpatterns }
             }
 

src/librustc_passes/rvalue_promotion.rs

@@ -376,7 +376,7 @@ fn check_expr_kind<'a, 'tcx>(
             let def = v.tables.qpath_def(qpath, e.hir_id);
             match def {
                 Def::VariantCtor(..) | Def::StructCtor(..) |
-                Def::Fn(..) | Def::Method(..) => Promotable,
+                Def::Fn(..) | Def::Method(..) | Def::SelfCtor(..) => Promotable,
 
                 // References to a static that are themselves within a static
                 // are inherently promotable with the exception
@@ -441,7 +441,8 @@ fn check_expr_kind<'a, 'tcx>(
             };
             let def_result = match def {
                 Def::StructCtor(_, CtorKind::Fn) |
-                Def::VariantCtor(_, CtorKind::Fn) => Promotable,
+                Def::VariantCtor(_, CtorKind::Fn) |
+                Def::SelfCtor(..) => Promotable,
                 Def::Fn(did) => {
                     v.handle_const_fn_call(did, node_ty, e.span)
                 }