Auto merge of #57501 - petrochenkov:highvar, r=<try>

[WIP] High priority resolutions for associated variants

cc #56225 (comment)

Author: bors

src/librustc/lint/builtin.rs

@@ -149,6 +149,12 @@ declare_lint! {
     "safe access to extern statics was erroneously allowed"
 }
 
+declare_lint! {
+    pub TYPE_VS_VARIANT_AMBIGUITY,
+    Forbid,
+    "type vs variant ambiguity"
+}
+
 declare_lint! {
     pub SAFE_PACKED_BORROWS,
     Warn,
@@ -400,6 +406,7 @@ impl LintPass for HardwiredLints {
             CONST_ERR,
             RENAMED_AND_REMOVED_LINTS,
             SAFE_EXTERN_STATICS,
+            TYPE_VS_VARIANT_AMBIGUITY,
             SAFE_PACKED_BORROWS,
             PATTERNS_IN_FNS_WITHOUT_BODY,
             LEGACY_DIRECTORY_OWNERSHIP,

src/librustc_typeck/astconv.rs

@@ -1288,7 +1288,8 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                                      span: Span,
                                      ty: Ty<'tcx>,
                                      ty_path_def: Def,
-                                     item_segment: &hir::PathSegment)
+                                     item_segment: &hir::PathSegment,
+                                     permit_variants: bool)
                                      -> (Ty<'tcx>, Def)
     {
         let tcx = self.tcx();
@@ -1298,11 +1299,38 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
 
         self.prohibit_generics(slice::from_ref(item_segment));
 
+        // Check if we have an enum variant here.
+        match ty.sty {
+            ty::Adt(adt_def, _) if adt_def.is_enum() => {
+                let variant_def = adt_def.variants.iter().find(|vd| {
+                    tcx.hygienic_eq(assoc_name, vd.ident, adt_def.did)
+                });
+                if let Some(variant_def) = variant_def {
+                    if permit_variants {
+                        check_type_alias_enum_variants_enabled(tcx, span);
+
+                        let def = Def::Variant(variant_def.did);
+                        tcx.check_stability(def.def_id(), Some(ref_id), span);
+                        return (ty, def);
+                    } else {
+                        use rustc::lint::builtin::TYPE_VS_VARIANT_AMBIGUITY;
+                        tcx.lint_node(
+                            TYPE_VS_VARIANT_AMBIGUITY,
+                            ref_id,
+                            span,
+                            "type vs variant ambiguity",
+                        );
+                    }
+                }
+            },
+            _ => (),
+        }
+
         // Find the type of the associated item, and the trait where the associated
         // item is declared.
         let bound = match (&ty.sty, ty_path_def) {
             (_, Def::SelfTy(Some(_), Some(impl_def_id))) => {
-                // `Self` in an impl of a trait -- we have a concrete self type and a
+                // `Self` in an impl of a trait -- we have a concrete `self` type and a
                 // trait reference.
                 let trait_ref = match tcx.impl_trait_ref(impl_def_id) {
                     Some(trait_ref) => trait_ref,
@@ -1354,23 +1382,6 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 return (tcx.types.err, Def::Err);
             }
             _ => {
-                // Check if we have an enum variant.
-                match ty.sty {
-                    ty::Adt(adt_def, _) if adt_def.is_enum() => {
-                        let variant_def = adt_def.variants.iter().find(|vd| {
-                            tcx.hygienic_eq(assoc_name, vd.ident, adt_def.did)
-                        });
-                        if let Some(variant_def) = variant_def {
-                            check_type_alias_enum_variants_enabled(tcx, span);
-
-                            let def = Def::Variant(variant_def.did);
-                            tcx.check_stability(def.def_id(), Some(ref_id), span);
-                            return (ty, def);
-                        }
-                    },
-                    _ => (),
-                }
-
                 // Don't print `TyErr` to the user.
                 if !ty.references_error() {
                     self.report_ambiguous_associated_type(span,
@@ -1773,7 +1784,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> dyn AstConv<'gcx, 'tcx> + 'o {
                 } else {
                     Def::Err
                 };
-                self.associated_path_def_to_ty(ast_ty.id, ast_ty.span, ty, def, segment).0
+                self.associated_path_def_to_ty(ast_ty.id, ast_ty.span, ty, def, segment, false).0
             }
             hir::TyKind::Array(ref ty, ref length) => {
                 let length_def_id = tcx.hir().local_def_id(length.id);

src/librustc_typeck/check/method/mod.rs

@@ -408,45 +408,38 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
         let tcx = self.tcx;
 
-        let mode = probe::Mode::Path;
-        match self.probe_for_name(span, mode, method_name, IsSuggestion(false),
-                                  self_ty, expr_id, ProbeScope::TraitsInScope) {
-            Ok(pick) => {
-                debug!("resolve_ufcs: pick={:?}", pick);
-                if let Some(import_id) = pick.import_id {
-                    let import_def_id = tcx.hir().local_def_id(import_id);
-                    debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id);
-                    Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
-                                                .unwrap().insert(import_def_id);
+        // Check if we have an enum variant here.
+        match self_ty.sty {
+            ty::Adt(adt_def, _) if adt_def.is_enum() => {
+                let variant_def = adt_def.variants.iter().find(|vd| {
+                    tcx.hygienic_eq(method_name, vd.ident, adt_def.did)
+                });
+                if let Some(variant_def) = variant_def {
+                    check_type_alias_enum_variants_enabled(tcx, span);
+
+                    let def = Def::VariantCtor(variant_def.did, variant_def.ctor_kind);
+                    tcx.check_stability(def.def_id(), Some(expr_id), span);
+                    return Ok(def);
                 }
+            },
+            _ => (),
+        }
 
-                let def = pick.item.def();
-                debug!("resolve_ufcs: def={:?}", def);
-                tcx.check_stability(def.def_id(), Some(expr_id), span);
-
-                Ok(def)
-            }
-            Err(err) => {
-                // Check if we have an enum variant.
-                match self_ty.sty {
-                    ty::Adt(adt_def, _) if adt_def.is_enum() => {
-                        let variant_def = adt_def.variants.iter().find(|vd| {
-                            tcx.hygienic_eq(method_name, vd.ident, adt_def.did)
-                        });
-                        if let Some(variant_def) = variant_def {
-                            check_type_alias_enum_variants_enabled(tcx, span);
-
-                            let def = Def::VariantCtor(variant_def.did, variant_def.ctor_kind);
-                            tcx.check_stability(def.def_id(), Some(expr_id), span);
-                            return Ok(def);
-                        }
-                    },
-                    _ => (),
-                }
+        let mode = probe::Mode::Path;
+        let pick = self.probe_for_name(span, mode, method_name, IsSuggestion(false),
+                                       self_ty, expr_id, ProbeScope::TraitsInScope)?;
 
-                Err(err)
-            }
+        if let Some(import_id) = pick.import_id {
+            let import_def_id = tcx.hir().local_def_id(import_id);
+            debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id);
+            Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
+                                         .unwrap().insert(import_def_id);
         }
+
+        let def = pick.item.def();
+        tcx.check_stability(def.def_id(), Some(expr_id), span);
+
+        Ok(def)
     }
 
     /// Find item with name `item_name` defined in impl/trait `def_id`

src/librustc_typeck/check/mod.rs

@@ -4623,7 +4623,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                     Def::Err
                 };
                 let (ty, def) = AstConv::associated_path_def_to_ty(self, node_id, path_span,
-                                                                   ty, def, segment);
+                                                                   ty, def, segment, true);
 
                 // Write back the new resolution.
                 let hir_id = self.tcx.hir().node_to_hir_id(node_id);

src/librustc_typeck/lib.rs

@@ -111,7 +111,7 @@ use rustc::infer::InferOk;
 use rustc::lint;
 use rustc::middle;
 use rustc::session;
-use rustc::session::config::nightly_options;
+// use rustc::session::config::nightly_options;
 use rustc::traits::{ObligationCause, ObligationCauseCode, TraitEngine, TraitEngineExt};
 use rustc::ty::subst::Substs;
 use rustc::ty::{self, Ty, TyCtxt};
@@ -130,20 +130,20 @@ pub struct TypeAndSubsts<'tcx> {
     ty: Ty<'tcx>,
 }
 
-fn check_type_alias_enum_variants_enabled<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'tcx>,
-                                                          span: Span) {
-    if !tcx.features().type_alias_enum_variants {
-        let mut err = tcx.sess.struct_span_err(
-            span,
-            "enum variants on type aliases are experimental"
-        );
-        if nightly_options::is_nightly_build() {
-            help!(&mut err,
-                "add `#![feature(type_alias_enum_variants)]` to the \
-                crate attributes to enable");
-        }
-        err.emit();
-    }
+fn check_type_alias_enum_variants_enabled<'a, 'gcx, 'tcx>(_tcx: TyCtxt<'a, 'gcx, 'tcx>,
+                                                          _span: Span) {
+    // if !tcx.features().type_alias_enum_variants {
+    //     let mut err = tcx.sess.struct_span_err(
+    //         span,
+    //         "enum variants on type aliases are experimental"
+    //     );
+    //     if nightly_options::is_nightly_build() {
+    //         help!(&mut err,
+    //             "add `#![feature(type_alias_enum_variants)]` to the \
+    //             crate attributes to enable");
+    //     }
+    //     err.emit();
+    // }
 }
 
 fn require_c_abi_if_variadic(tcx: TyCtxt,

src/test/ui/feature-gates/feature-gate-type_alias_enum_variants.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+// compile-pass
+
 enum Foo {
     Bar(i32),
     Baz { i: i32 },

src/test/ui/feature-gates/feature-gate-type_alias_enum_variants.stderr

@@ -0,0 +1,13 @@
+#![feature(type_alias_enum_variants)]
+
+enum E {
+    V(u8)
+}
+
+impl E {
+    fn V() {}
+}
+
+fn main() {
+    <E>::V(); //~ ERROR this function takes 1 parameter but 0 parameters were supplied
+}

src/test/ui/type-alias-enum-variants-priority-2.rs

@@ -0,0 +1,12 @@
+error[E0061]: this function takes 1 parameter but 0 parameters were supplied
+  --> $DIR/type-alias-enum-variants-priority-2.rs:12:5
+   |
+LL |     V(u8)
+   |     ----- defined here
+...
+LL |     <E>::V(); //~ ERROR this function takes 1 parameter but 0 parameters were supplied
+   |     ^^^^^^^^ expected 1 parameter
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0061`.

src/test/ui/type-alias-enum-variants-priority-2.stderr

@@ -0,0 +1,17 @@
+#![feature(type_alias_enum_variants)]
+
+enum E {
+    V(u8)
+}
+
+trait Tr {
+    type V;
+    fn f() -> Self::V;
+}
+
+impl Tr for E {
+    type V = u8;
+    fn f() -> Self::V { loop {} } //~ ERROR type vs variant ambiguity
+}
+
+fn main() {}