Auto merge of #36871 - petrochenkov:pdderr, r=nikomatsakis

Turn compatibility lint `match_of_unit_variant_via_paren_dotdot` into a hard error

The lint was introduced 10 months ago and made deny-by-default 7 months ago.
In case someone is still using it, #36868 contains a stable replacement.

r? @nikomatsakis

Author: bors

src/librustc/hir/lowering.rs

@@ -44,9 +44,8 @@ use hir;
 use hir::map::Definitions;
 use hir::map::definitions::DefPathData;
 use hir::def_id::{DefIndex, DefId};
-use hir::def::{Def, CtorKind, PathResolution};
+use hir::def::{Def, PathResolution};
 use session::Session;
-use lint;
 
 use std::collections::BTreeMap;
 use std::iter;
@@ -857,22 +856,8 @@ impl<'a> LoweringContext<'a> {
                 }
                 PatKind::Lit(ref e) => hir::PatKind::Lit(self.lower_expr(e)),
                 PatKind::TupleStruct(ref path, ref pats, ddpos) => {
-                    match self.resolver.get_resolution(p.id).map(|d| d.base_def) {
-                        Some(def @ Def::StructCtor(_, CtorKind::Const)) |
-                        Some(def @ Def::VariantCtor(_, CtorKind::Const)) => {
-                            // Temporarily lower `UnitVariant(..)` into `UnitVariant`
-                            // for backward compatibility.
-                            let msg = format!("expected tuple struct/variant, found {} `{}`",
-                                            def.kind_name(), path);
-                            self.sess.add_lint(
-                                lint::builtin::MATCH_OF_UNIT_VARIANT_VIA_PAREN_DOTDOT,
-                                p.id, p.span, msg
-                            );
-                            hir::PatKind::Path(None, self.lower_path(path))
-                        }
-                        _ => hir::PatKind::TupleStruct(self.lower_path(path),
+                    hir::PatKind::TupleStruct(self.lower_path(path),
                                         pats.iter().map(|x| self.lower_pat(x)).collect(), ddpos)
-                    }
                 }
                 PatKind::Path(ref opt_qself, ref path) => {
                     let opt_qself = opt_qself.as_ref().map(|qself| {

src/librustc/lint/builtin.rs

@@ -143,12 +143,6 @@ declare_lint! {
      the struct or enum has `#[derive(PartialEq, Eq)]`"
 }
 
-declare_lint! {
-    pub MATCH_OF_UNIT_VARIANT_VIA_PAREN_DOTDOT,
-    Deny,
-    "unit struct or enum variant erroneously allowed to match via path::ident(..)"
-}
-
 declare_lint! {
     pub RAW_POINTER_DERIVE,
     Warn,
@@ -226,7 +220,6 @@ impl LintPass for HardwiredLints {
             INVALID_TYPE_PARAM_DEFAULT,
             ILLEGAL_FLOATING_POINT_CONSTANT_PATTERN,
             ILLEGAL_STRUCT_OR_ENUM_CONSTANT_PATTERN,
-            MATCH_OF_UNIT_VARIANT_VIA_PAREN_DOTDOT,
             CONST_ERR,
             RAW_POINTER_DERIVE,
             TRANSMUTE_FROM_FN_ITEM_TYPES,

src/librustc_lint/lib.rs

@@ -172,11 +172,6 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
             id: LintId::of(SUPER_OR_SELF_IN_GLOBAL_PATH),
             reference: "PR #32403 <https://github.com/rust-lang/rust/pull/32403>",
         },
-        FutureIncompatibleInfo {
-            id: LintId::of(MATCH_OF_UNIT_VARIANT_VIA_PAREN_DOTDOT),
-            reference: "RFC 218 <https://github.com/rust-lang/rfcs/blob/\
-                        master/text/0218-empty-struct-with-braces.md>",
-        },
         FutureIncompatibleInfo {
             id: LintId::of(TRANSMUTE_FROM_FN_ITEM_TYPES),
             reference: "issue #19925 <https://github.com/rust-lang/rust/issues/19925>",

src/librustc_resolve/lib.rs

@@ -2412,15 +2412,11 @@ impl<'a> Resolver<'a> {
                     self.record_def(pat.id, resolution);
                 }
 
-                PatKind::TupleStruct(ref path, ref pats, ddpos) => {
+                PatKind::TupleStruct(ref path, ..) => {
                     self.resolve_pattern_path(pat.id, None, path, ValueNS, |def| {
                         match def {
                             Def::StructCtor(_, CtorKind::Fn) |
                             Def::VariantCtor(_, CtorKind::Fn) => true,
-                            // `UnitVariant(..)` is accepted for backward compatibility.
-                            Def::StructCtor(_, CtorKind::Const) |
-                            Def::VariantCtor(_, CtorKind::Const)
-                                if pats.is_empty() && ddpos.is_some() => true,
                             _ => false,
                         }
                     }, "tuple struct/variant");

src/test/compile-fail/empty-struct-unit-pat-2.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-// Can't use unit struct as enum pattern
+// Can't use unit struct as tuple struct pattern
 
 // aux-build:empty-struct.rs
 
@@ -23,30 +23,39 @@ enum E {
     Empty4
 }
 
-// remove attribute after warning cycle and promoting warnings to errors
 fn main() {
     let e2 = Empty2;
     let e4 = E::Empty4;
     let xe2 = XEmpty2;
     let xe4 = XE::XEmpty4;
 
+    match e2 {
+        Empty2() => () //~ ERROR expected tuple struct/variant, found unit struct `Empty2`
+    }
+    match xe2 {
+        XEmpty2() => () //~ ERROR expected tuple struct/variant, found unit struct `XEmpty2`
+    }
     match e2 {
         Empty2(..) => () //~ ERROR expected tuple struct/variant, found unit struct `Empty2`
-            //~^ WARNING hard error
     }
     match xe2 {
         XEmpty2(..) => () //~ ERROR expected tuple struct/variant, found unit struct `XEmpty2`
-            //~^ WARNING hard error
     }
 
+    match e4 {
+        E::Empty4() => () //~ ERROR expected tuple struct/variant, found unit variant `E::Empty4`
+    }
+    match xe4 {
+        XE::XEmpty4() => (),
+        //~^ ERROR expected tuple struct/variant, found unit variant `XE::XEmpty4`
+        _ => {},
+    }
     match e4 {
         E::Empty4(..) => () //~ ERROR expected tuple struct/variant, found unit variant `E::Empty4`
-            //~^ WARNING hard error
     }
     match xe4 {
         XE::XEmpty4(..) => (),
-            //~^ ERROR expected tuple struct/variant, found unit variant `XE::XEmpty4`
-            //~| WARNING hard error
+        //~^ ERROR expected tuple struct/variant, found unit variant `XE::XEmpty4`
         _ => {},
     }
 }

src/test/compile-fail/empty-struct-unit-pat-1.rs renamed to src/test/compile-fail/empty-struct-unit-pat.rs

@@ -8,8 +8,6 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![allow(match_of_unit_variant_via_paren_dotdot)]
-
 enum E {
     A,
     B,
@@ -18,7 +16,7 @@ enum E {
 fn main() {
     match None {
         None => {}
-        Some(E::A(..)) => {}
-        Some(E::B(..)) => {}
+        Some(E::A(..)) => {} //~ ERROR expected tuple struct/variant, found unit variant `E::A`
+        Some(E::B(..)) => {} //~ ERROR expected tuple struct/variant, found unit variant `E::B`
     }
 }