Auto merge of #37035 - petrochenkov:selfstruct, r=eddyb

Support `Self` in struct expressions and patterns

Struct expressions and patterns generally support type aliases `Alias { field: 10 }` i.e. they already have to work with `ty::Ty` to do their job. `Self` is a type alias (when it's not a type parameter) => struct expressions and patterns should support `Self`.

Typical example:
```
impl MyStruct {
    fn new() -> Self {
        Self { a: 10, b: "Hello" }
    }
}
```

The first commit does some preparations and cleanups, see the commit message for  details.
This also fixes couple of bugs related to aliases in struct paths (fixes #36286).

EDIT:
Since struct expressions and patterns always work with `ty::Ty` now, associated paths in them are also supported. If associated type `A::B` successfully resolves to a struct (or union) type, then `A::B { /* fields */ }` is a valid expression/pattern. This will become more important when enum variants are treated as [associated items](#26264 (comment)).

r? @eddyb

src/librustc/middle/expr_use_visitor.rs

@@ -1017,7 +1017,7 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
                     delegate.matched_pat(pat, downcast_cmt, match_mode);
                 }
                 Some(Def::Struct(..)) | Some(Def::StructCtor(..)) | Some(Def::Union(..)) |
-                Some(Def::TyAlias(..)) | Some(Def::AssociatedTy(..)) => {
+                Some(Def::TyAlias(..)) | Some(Def::AssociatedTy(..)) | Some(Def::SelfTy(..)) => {
                     debug!("struct cmt_pat={:?} pat={:?}", cmt_pat, pat);
                     delegate.matched_pat(pat, cmt_pat, match_mode);
                 }

src/librustc/ty/mod.rs

@@ -1698,7 +1698,7 @@ impl<'a, 'gcx, 'tcx, 'container> AdtDefData<'gcx, 'container> {
         match def {
             Def::Variant(vid) | Def::VariantCtor(vid, ..) => self.variant_with_id(vid),
             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
-            Def::TyAlias(..) | Def::AssociatedTy(..) => self.struct_variant(),
+            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => self.struct_variant(),
             _ => bug!("unexpected def {:?} in variant_of_def", def)
         }
     }

src/librustc/util/ppaux.rs

@@ -14,7 +14,7 @@ use ty::{BrAnon, BrEnv, BrFresh, BrNamed};
 use ty::{TyBool, TyChar, TyAdt};
 use ty::{TyError, TyStr, TyArray, TySlice, TyFloat, TyFnDef, TyFnPtr};
 use ty::{TyParam, TyRawPtr, TyRef, TyNever, TyTuple};
-use ty::TyClosure;
+use ty::{TyClosure, TyProjection, TyAnon};
 use ty::{TyBox, TyTrait, TyInt, TyUint, TyInfer};
 use ty::{self, Ty, TyCtxt, TypeFoldable};
 use ty::fold::{TypeFolder, TypeVisitor};
@@ -879,8 +879,8 @@ impl<'tcx> fmt::Display for ty::TypeVariants<'tcx> {
                 })
             }
             TyTrait(ref data) => write!(f, "{}", data),
-            ty::TyProjection(ref data) => write!(f, "{}", data),
-            ty::TyAnon(def_id, substs) => {
+            TyProjection(ref data) => write!(f, "{}", data),
+            TyAnon(def_id, substs) => {
                 ty::tls::with(|tcx| {
                     // Grab the "TraitA + TraitB" from `impl TraitA + TraitB`,
                     // by looking up the projections associated with the def_id.

src/librustc_const_eval/pattern.rs

@@ -436,7 +436,7 @@ impl<'a, 'gcx, 'tcx> PatternContext<'a, 'gcx, 'tcx> {
             }
 
             Def::Struct(..) | Def::StructCtor(..) | Def::Union(..) |
-            Def::TyAlias(..) | Def::AssociatedTy(..) => {
+            Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => {
                 PatternKind::Leaf { subpatterns: subpatterns }
             }
 

src/librustc_passes/consts.rs

@@ -565,9 +565,11 @@ fn check_expr<'a, 'tcx>(v: &mut CheckCrateVisitor<'a, 'tcx>, e: &hir::Expr, node
             }
         }
         hir::ExprStruct(..) => {
-            // unsafe_cell_type doesn't necessarily exist with no_core
-            if Some(v.tcx.expect_def(e.id).def_id()) == v.tcx.lang_items.unsafe_cell_type() {
-                v.add_qualif(ConstQualif::MUTABLE_MEM);
+            if let ty::TyAdt(adt, ..) = v.tcx.expr_ty(e).sty {
+                // unsafe_cell_type doesn't necessarily exist with no_core
+                if Some(adt.did) == v.tcx.lang_items.unsafe_cell_type() {
+                    v.add_qualif(ConstQualif::MUTABLE_MEM);
+                }
             }
         }
 

src/librustc_resolve/diagnostics.rs

@@ -860,31 +860,6 @@ match (A, B, C) {
 ```
 "##,
 
-E0422: r##"
-You are trying to use an identifier that is either undefined or not a struct.
-
-Erroneous code example:
-
-``` compile_fail,E0422
-fn main () {
-    let x = Foo { x: 1, y: 2 };
-}
-```
-
-In this case, `Foo` is undefined, so it inherently isn't anything, and
-definitely not a struct.
-
-```compile_fail,E0422
-fn main () {
-    let foo = 1;
-    let x = foo { x: 1, y: 2 };
-}
-```
-
-In this case, `foo` is defined, but is not a struct, so Rust can't use it as
-one.
-"##,
-
 E0423: r##"
 A `struct` variant name was used like a function name.
 
@@ -1503,6 +1478,7 @@ register_diagnostics! {
 //  E0419, merged into 531
 //  E0420, merged into 532
 //  E0421, merged into 531
+//  E0422, merged into 531/532
     E0531, // unresolved pattern path kind `name`
     E0532, // expected pattern path kind, found another pattern path kind
 //  E0427, merged into 530

src/librustc_resolve/lib.rs

@@ -129,8 +129,6 @@ enum ResolutionError<'a> {
     IdentifierBoundMoreThanOnceInParameterList(&'a str),
     /// error E0416: identifier is bound more than once in the same pattern
     IdentifierBoundMoreThanOnceInSamePattern(&'a str),
-    /// error E0422: does not name a struct
-    DoesNotNameAStruct(&'a str),
     /// error E0423: is a struct variant name, but this expression uses it like a function name
     StructVariantUsedAsFunction(&'a str),
     /// error E0424: `self` is not available in a static method
@@ -336,15 +334,6 @@ fn resolve_struct_error<'b, 'a: 'b, 'c>(resolver: &'b Resolver<'a>,
             err.span_label(span, &format!("used in a pattern more than once"));
             err
         }
-        ResolutionError::DoesNotNameAStruct(name) => {
-            let mut err = struct_span_err!(resolver.session,
-                             span,
-                             E0422,
-                             "`{}` does not name a structure",
-                             name);
-            err.span_label(span, &format!("not a structure"));
-            err
-        }
         ResolutionError::StructVariantUsedAsFunction(path_name) => {
             let mut err = struct_span_err!(resolver.session,
                              span,
@@ -2383,6 +2372,18 @@ impl<'a> Resolver<'a> {
         self.record_def(pat_id, resolution);
     }
 
+    fn resolve_struct_path(&mut self, node_id: NodeId, path: &Path) {
+        // Resolution logic is equivalent for expressions and patterns,
+        // reuse `resolve_pattern_path` for both.
+        self.resolve_pattern_path(node_id, None, path, TypeNS, |def| {
+            match def {
+                Def::Struct(..) | Def::Union(..) | Def::Variant(..) |
+                Def::TyAlias(..) | Def::AssociatedTy(..) | Def::SelfTy(..) => true,
+                _ => false,
+            }
+        }, "struct, variant or union type");
+    }
+
     fn resolve_pattern(&mut self,
                        pat: &Pat,
                        pat_src: PatternSource,
@@ -2460,13 +2461,7 @@ impl<'a> Resolver<'a> {
                 }
 
                 PatKind::Struct(ref path, ..) => {
-                    self.resolve_pattern_path(pat.id, None, path, TypeNS, |def| {
-                        match def {
-                            Def::Struct(..) | Def::Union(..) | Def::Variant(..) |
-                            Def::TyAlias(..) | Def::AssociatedTy(..) => true,
-                            _ => false,
-                        }
-                    }, "variant, struct or type alias");
+                    self.resolve_struct_path(pat.id, path);
                 }
 
                 _ => {}
@@ -3024,23 +3019,7 @@ impl<'a> Resolver<'a> {
             }
 
             ExprKind::Struct(ref path, ..) => {
-                // Resolve the path to the structure it goes to. We don't
-                // check to ensure that the path is actually a structure; that
-                // is checked later during typeck.
-                match self.resolve_path(expr.id, path, 0, TypeNS) {
-                    Ok(definition) => self.record_def(expr.id, definition),
-                    Err(true) => self.record_def(expr.id, err_path_resolution()),
-                    Err(false) => {
-                        debug!("(resolving expression) didn't find struct def",);
-
-                        resolve_error(self,
-                                      path.span,
-                                      ResolutionError::DoesNotNameAStruct(
-                                                                &path_names_to_string(path, 0))
-                                     );
-                        self.record_def(expr.id, err_path_resolution());
-                    }
-                }
+                self.resolve_struct_path(expr.id, path);
 
                 visit::walk_expr(self, expr);
             }

src/librustc_save_analysis/dump_visitor.rs

@@ -1493,7 +1493,8 @@ impl<'l, 'tcx: 'l, 'll, D: Dump +'ll> Visitor for DumpVisitor<'l, 'tcx, 'll, D>
                 Def::StructCtor(..) | Def::VariantCtor(..) |
                 Def::Const(..) | Def::AssociatedConst(..) |
                 Def::Struct(..) | Def::Variant(..) |
-                Def::TyAlias(..) | Def::AssociatedTy(..) => {
+                Def::TyAlias(..) | Def::AssociatedTy(..) |
+                Def::SelfTy(..) => {
                     paths_to_process.push((id, p.clone(), Some(ref_kind)))
                 }
                 def => error!("unexpected definition kind when processing collected paths: {:?}",

src/librustc_typeck/astconv.rs

@@ -1484,7 +1484,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                       def: Def,
                       opt_self_ty: Option<Ty<'tcx>>,
                       base_path_ref_id: ast::NodeId,
-                      base_segments: &[hir::PathSegment])
+                      base_segments: &[hir::PathSegment],
+                      permit_variants: bool)
                       -> Ty<'tcx> {
         let tcx = self.tcx();
 
@@ -1515,6 +1516,16 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                                     did,
                                     base_segments.last().unwrap())
             }
+            Def::Variant(did) if permit_variants => {
+                // Convert "variant type" as if it were a real type.
+                // The resulting `Ty` is type of the variant's enum for now.
+                tcx.prohibit_type_params(base_segments.split_last().unwrap().1);
+                self.ast_path_to_ty(rscope,
+                                    span,
+                                    param_mode,
+                                    tcx.parent_def_id(did).unwrap(),
+                                    base_segments.last().unwrap())
+            }
             Def::TyParam(did) => {
                 tcx.prohibit_type_params(base_segments);
 
@@ -1604,7 +1615,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                                       opt_self_ty: Option<Ty<'tcx>>,
                                       base_path_ref_id: ast::NodeId,
                                       base_segments: &[hir::PathSegment],
-                                      assoc_segments: &[hir::PathSegment])
+                                      assoc_segments: &[hir::PathSegment],
+                                      permit_variants: bool)
                                       -> (Ty<'tcx>, Def) {
         // Convert the base type.
         debug!("finish_resolving_def_to_ty(base_def={:?}, \
@@ -1619,7 +1631,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                                           base_def,
                                           opt_self_ty,
                                           base_path_ref_id,
-                                          base_segments);
+                                          base_segments,
+                                          permit_variants);
         debug!("finish_resolving_def_to_ty: base_def_to_ty returned {:?}", base_ty);
 
         // If any associated type segments remain, attempt to resolve them.
@@ -1775,7 +1788,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                                                                 opt_self_ty,
                                                                 ast_ty.id,
                                                                 &path.segments[..base_ty_end],
-                                                                &path.segments[base_ty_end..]);
+                                                                &path.segments[base_ty_end..],
+                                                                false);
 
                 // Write back the new resolution.
                 if path_res.depth != 0 {

src/librustc_typeck/check/_match.rs

@@ -489,8 +489,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                         expected: Ty<'tcx>) -> Ty<'tcx>
     {
         // Resolve the path and check the definition for errors.
-        let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(path, pat.id,
-                                                                                 pat.span) {
+        let (variant, pat_ty) = if let Some(variant_ty) = self.check_struct_path(path, pat.id) {
             variant_ty
         } else {
             for field in fields {