Auto merge of #31581 - petrochenkov:patrefact, r=Manishearth

cc #31487 (comment)
plugin-[breaking-change]

The first commit renames `ast::Pat_` to `ast::PatKind` and uses its variants in enum qualified form. I've also taken the opportunity and renamed `PatKind::Region` into `PatKind::Ref`.

The second commit splits `PatKind::Enum` into `PatKind::TupleStruct` and `PatKind::UnitStruct`.
So, pattern kinds now correspond to their struct/variant kinds - `Struct`, `TupleStruct` and `UnitStruct`.
@nikomatsakis @nrc @arielb1 Are you okay with this naming scheme?
An alternative possible naming scheme is `PatKind::StructVariant`, `PatKind::TupleVariant`, `PatKind::UnitVariant` (it's probably closer to the common use, but I like it less).

I intend to apply these changes to HIR later, they should not necessarily go in the same nightly with #31487
r? @Manishearth

src/librustc_front/lowering.rs

@@ -913,26 +913,29 @@ pub fn lower_pat(lctx: &LoweringContext, p: &Pat) -> P<hir::Pat> {
     P(hir::Pat {
         id: p.id,
         node: match p.node {
-            PatWild => hir::PatWild,
-            PatIdent(ref binding_mode, pth1, ref sub) => {
+            PatKind::Wild => hir::PatWild,
+            PatKind::Ident(ref binding_mode, pth1, ref sub) => {
                 hir::PatIdent(lower_binding_mode(lctx, binding_mode),
                               respan(pth1.span, lower_ident(lctx, pth1.node)),
                               sub.as_ref().map(|x| lower_pat(lctx, x)))
             }
-            PatLit(ref e) => hir::PatLit(lower_expr(lctx, e)),
-            PatEnum(ref pth, ref pats) => {
+            PatKind::Lit(ref e) => hir::PatLit(lower_expr(lctx, e)),
+            PatKind::TupleStruct(ref pth, ref pats) => {
                 hir::PatEnum(lower_path(lctx, pth),
                              pats.as_ref()
                                  .map(|pats| pats.iter().map(|x| lower_pat(lctx, x)).collect()))
             }
-            PatQPath(ref qself, ref pth) => {
+            PatKind::Path(ref pth) => {
+                hir::PatEnum(lower_path(lctx, pth), Some(hir::HirVec::new()))
+            }
+            PatKind::QPath(ref qself, ref pth) => {
                 let qself = hir::QSelf {
                     ty: lower_ty(lctx, &qself.ty),
                     position: qself.position,
                 };
                 hir::PatQPath(qself, lower_path(lctx, pth))
             }
-            PatStruct(ref pth, ref fields, etc) => {
+            PatKind::Struct(ref pth, ref fields, etc) => {
                 let pth = lower_path(lctx, pth);
                 let fs = fields.iter()
                                .map(|f| {
@@ -948,20 +951,22 @@ pub fn lower_pat(lctx: &LoweringContext, p: &Pat) -> P<hir::Pat> {
                                .collect();
                 hir::PatStruct(pth, fs, etc)
             }
-            PatTup(ref elts) => hir::PatTup(elts.iter().map(|x| lower_pat(lctx, x)).collect()),
-            PatBox(ref inner) => hir::PatBox(lower_pat(lctx, inner)),
-            PatRegion(ref inner, mutbl) => {
+            PatKind::Tup(ref elts) => {
+                hir::PatTup(elts.iter().map(|x| lower_pat(lctx, x)).collect())
+            }
+            PatKind::Box(ref inner) => hir::PatBox(lower_pat(lctx, inner)),
+            PatKind::Ref(ref inner, mutbl) => {
                 hir::PatRegion(lower_pat(lctx, inner), lower_mutability(lctx, mutbl))
             }
-            PatRange(ref e1, ref e2) => {
+            PatKind::Range(ref e1, ref e2) => {
                 hir::PatRange(lower_expr(lctx, e1), lower_expr(lctx, e2))
             }
-            PatVec(ref before, ref slice, ref after) => {
+            PatKind::Vec(ref before, ref slice, ref after) => {
                 hir::PatVec(before.iter().map(|x| lower_pat(lctx, x)).collect(),
                             slice.as_ref().map(|x| lower_pat(lctx, x)),
                             after.iter().map(|x| lower_pat(lctx, x)).collect())
             }
-            PatMac(_) => panic!("Shouldn't exist here"),
+            PatKind::Mac(_) => panic!("Shouldn't exist here"),
         },
         span: p.span,
     })

src/librustc_passes/const_fn.rs

@@ -13,7 +13,7 @@
 
 use rustc::session::{Session, CompileResult};
 
-use syntax::ast;
+use syntax::ast::{self, PatKind};
 use syntax::visit::{self, Visitor, FnKind};
 use syntax::codemap::Span;
 
@@ -104,8 +104,8 @@ impl<'a, 'v> Visitor<'v> for CheckConstFn<'a> {
         // Ensure the arguments are simple, not mutable/by-ref or patterns.
         for arg in &fd.inputs {
             match arg.pat.node {
-                ast::PatWild => {}
-                ast::PatIdent(ast::BindingMode::ByValue(ast::Mutability::Immutable), _, None) => {}
+                PatKind::Wild => {}
+                PatKind::Ident(ast::BindingMode::ByValue(ast::Mutability::Immutable), _, None) => {}
                 _ => {
                     span_err!(self.sess, arg.pat.span, E0022,
                               "arguments of constant functions can only \

src/librustc_trans/save/dump_csv.rs

@@ -40,7 +40,7 @@ use std::fs::File;
 use std::hash::*;
 use std::collections::HashSet;
 
-use syntax::ast::{self, NodeId};
+use syntax::ast::{self, NodeId, PatKind};
 use syntax::codemap::*;
 use syntax::parse::token::{self, keywords};
 use syntax::visit::{self, Visitor};
@@ -780,7 +780,7 @@ impl <'l, 'tcx> DumpCsvVisitor<'l, 'tcx> {
 
     fn process_pat(&mut self, p: &ast::Pat) {
         match p.node {
-            ast::PatStruct(ref path, ref fields, _) => {
+            PatKind::Struct(ref path, ref fields, _) => {
                 visit::walk_path(self, path);
                 let adt = self.tcx.node_id_to_type(p.id).ty_adt_def().unwrap();
                 let def = self.tcx.def_map.borrow()[&p.id].full_def();

src/librustc_trans/save/mod.rs

@@ -21,7 +21,7 @@ use rustc_front::{hir, lowering};
 use rustc::front::map::NodeItem;
 use rustc::session::config::CrateType::CrateTypeExecutable;
 
-use syntax::ast::{self, NodeId};
+use syntax::ast::{self, NodeId, PatKind};
 use syntax::ast_util;
 use syntax::codemap::*;
 use syntax::parse::token::{self, keywords};
@@ -758,16 +758,17 @@ impl PathCollector {
 impl<'v> Visitor<'v> for PathCollector {
     fn visit_pat(&mut self, p: &ast::Pat) {
         match p.node {
-            ast::PatStruct(ref path, _, _) => {
+            PatKind::Struct(ref path, _, _) => {
                 self.collected_paths.push((p.id, path.clone(),
                                            ast::Mutability::Mutable, recorder::TypeRef));
             }
-            ast::PatEnum(ref path, _) |
-            ast::PatQPath(_, ref path) => {
+            PatKind::TupleStruct(ref path, _) |
+            PatKind::Path(ref path) |
+            PatKind::QPath(_, ref path) => {
                 self.collected_paths.push((p.id, path.clone(),
                                            ast::Mutability::Mutable, recorder::VarRef));
             }
-            ast::PatIdent(bm, ref path1, _) => {
+            PatKind::Ident(bm, ref path1, _) => {
                 debug!("PathCollector, visit ident in pat {}: {:?} {:?}",
                        path1.node,
                        p.span,

src/libsyntax/ast.rs

@@ -10,7 +10,6 @@
 
 // The Rust abstract syntax tree.
 
-pub use self::Pat_::*;
 pub use self::StructFieldKind::*;
 pub use self::TyParamBound::*;
 pub use self::UnsafeSource::*;
@@ -521,7 +520,7 @@ pub struct Block {
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash)]
 pub struct Pat {
     pub id: NodeId,
-    pub node: Pat_,
+    pub node: PatKind,
     pub span: Span,
 }
 
@@ -552,47 +551,53 @@ pub enum BindingMode {
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
-pub enum Pat_ {
+pub enum PatKind {
     /// Represents a wildcard pattern (`_`)
-    PatWild,
+    Wild,
 
-    /// A PatIdent may either be a new bound variable,
-    /// or a nullary enum (in which case the third field
-    /// is None).
+    /// A `PatKind::Ident` may either be a new bound variable,
+    /// or a unit struct/variant pattern, or a const pattern (in the last two cases
+    /// the third field must be `None`).
     ///
-    /// In the nullary enum case, the parser can't determine
+    /// In the unit or const pattern case, the parser can't determine
     /// which it is. The resolver determines this, and
-    /// records this pattern's NodeId in an auxiliary
-    /// set (of "PatIdents that refer to nullary enums")
-    PatIdent(BindingMode, SpannedIdent, Option<P<Pat>>),
+    /// records this pattern's `NodeId` in an auxiliary
+    /// set (of "PatIdents that refer to unit patterns or constants").
+    Ident(BindingMode, SpannedIdent, Option<P<Pat>>),
 
+    /// A struct or struct variant pattern, e.g. `Variant {x, y, ..}`.
+    /// The `bool` is `true` in the presence of a `..`.
+    Struct(Path, Vec<Spanned<FieldPat>>, bool),
+
+    /// A tuple struct/variant pattern `Variant(x, y, z)`.
     /// "None" means a `Variant(..)` pattern where we don't bind the fields to names.
-    PatEnum(Path, Option<Vec<P<Pat>>>),
+    TupleStruct(Path, Option<Vec<P<Pat>>>),
+
+    /// A path pattern.
+    /// Such pattern can be resolved to a unit struct/variant or a constant.
+    Path(Path),
 
     /// An associated const named using the qualified path `<T>::CONST` or
     /// `<T as Trait>::CONST`. Associated consts from inherent impls can be
     /// referred to as simply `T::CONST`, in which case they will end up as
-    /// PatEnum, and the resolver will have to sort that out.
-    PatQPath(QSelf, Path),
+    /// PatKind::Enum, and the resolver will have to sort that out.
+    QPath(QSelf, Path),
 
-    /// Destructuring of a struct, e.g. `Foo {x, y, ..}`
-    /// The `bool` is `true` in the presence of a `..`
-    PatStruct(Path, Vec<Spanned<FieldPat>>, bool),
     /// A tuple pattern `(a, b)`
-    PatTup(Vec<P<Pat>>),
+    Tup(Vec<P<Pat>>),
     /// A `box` pattern
-    PatBox(P<Pat>),
+    Box(P<Pat>),
     /// A reference pattern, e.g. `&mut (a, b)`
-    PatRegion(P<Pat>, Mutability),
+    Ref(P<Pat>, Mutability),
     /// A literal
-    PatLit(P<Expr>),
+    Lit(P<Expr>),
     /// A range pattern, e.g. `1...2`
-    PatRange(P<Expr>, P<Expr>),
+    Range(P<Expr>, P<Expr>),
     /// `[a, b, ..i, y, z]` is represented as:
-    ///     `PatVec(box [a, b], Some(i), box [y, z])`
-    PatVec(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
+    ///     `PatKind::Vec(box [a, b], Some(i), box [y, z])`
+    Vec(Vec<P<Pat>>, Option<P<Pat>>, Vec<P<Pat>>),
     /// A macro pattern; pre-expansion
-    PatMac(Mac),
+    Mac(Mac),
 }
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
@@ -1609,7 +1614,7 @@ impl Arg {
             }),
             pat: P(Pat {
                 id: DUMMY_NODE_ID,
-                node: PatIdent(BindingMode::ByValue(mutability), path, None),
+                node: PatKind::Ident(BindingMode::ByValue(mutability), path, None),
                 span: span
             }),
             id: DUMMY_NODE_ID

src/libsyntax/ast_util.rs

@@ -69,7 +69,7 @@ pub fn ident_to_pat(id: NodeId, s: Span, i: Ident) -> P<Pat> {
     let spanned = codemap::Spanned{ span: s, node: i };
     P(Pat {
         id: id,
-        node: PatIdent(BindingMode::ByValue(Mutability::Immutable), spanned, None),
+        node: PatKind::Ident(BindingMode::ByValue(Mutability::Immutable), spanned, None),
         span: s
     })
 }
@@ -348,7 +348,7 @@ pub fn compute_id_range_for_fn_body(fk: FnKind,
 /// and false otherwise.
 pub fn pat_is_ident(pat: P<ast::Pat>) -> bool {
     match pat.node {
-        ast::PatIdent(..) => true,
+        PatKind::Ident(..) => true,
         _ => false,
     }
 }

src/libsyntax/ext/base.rs

@@ -11,7 +11,7 @@
 pub use self::SyntaxExtension::*;
 
 use ast;
-use ast::Name;
+use ast::{Name, PatKind};
 use codemap;
 use codemap::{CodeMap, Span, ExpnId, ExpnInfo, NO_EXPANSION};
 use errors::DiagnosticBuilder;
@@ -307,7 +307,7 @@ impl MacResult for MacEager {
                 return Some(P(ast::Pat {
                     id: ast::DUMMY_NODE_ID,
                     span: e.span,
-                    node: ast::PatLit(e),
+                    node: PatKind::Lit(e),
                 }));
             }
         }
@@ -359,7 +359,7 @@ impl DummyResult {
     pub fn raw_pat(sp: Span) -> ast::Pat {
         ast::Pat {
             id: ast::DUMMY_NODE_ID,
-            node: ast::PatWild,
+            node: PatKind::Wild,
             span: sp,
         }
     }

src/libsyntax/ext/build.rs

@@ -9,7 +9,7 @@
 // except according to those terms.
 
 use abi::Abi;
-use ast::{self, Ident, Generics, Expr, BlockCheckMode, UnOp};
+use ast::{self, Ident, Generics, Expr, BlockCheckMode, UnOp, PatKind};
 use attr;
 use codemap::{Span, respan, Spanned, DUMMY_SP, Pos};
 use ext::base::ExtCtxt;
@@ -166,7 +166,7 @@ pub trait AstBuilder {
     fn expr_err(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Expr>;
     fn expr_try(&self, span: Span, head: P<ast::Expr>) -> P<ast::Expr>;
 
-    fn pat(&self, span: Span, pat: ast::Pat_) -> P<ast::Pat>;
+    fn pat(&self, span: Span, pat: PatKind) -> P<ast::Pat>;
     fn pat_wild(&self, span: Span) -> P<ast::Pat>;
     fn pat_lit(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Pat>;
     fn pat_ident(&self, span: Span, ident: ast::Ident) -> P<ast::Pat>;
@@ -805,14 +805,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
     }
 
 
-    fn pat(&self, span: Span, pat: ast::Pat_) -> P<ast::Pat> {
+    fn pat(&self, span: Span, pat: PatKind) -> P<ast::Pat> {
         P(ast::Pat { id: ast::DUMMY_NODE_ID, node: pat, span: span })
     }
     fn pat_wild(&self, span: Span) -> P<ast::Pat> {
-        self.pat(span, ast::PatWild)
+        self.pat(span, PatKind::Wild)
     }
     fn pat_lit(&self, span: Span, expr: P<ast::Expr>) -> P<ast::Pat> {
-        self.pat(span, ast::PatLit(expr))
+        self.pat(span, PatKind::Lit(expr))
     }
     fn pat_ident(&self, span: Span, ident: ast::Ident) -> P<ast::Pat> {
         let binding_mode = ast::BindingMode::ByValue(ast::Mutability::Immutable);
@@ -823,20 +823,24 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
                               span: Span,
                               ident: ast::Ident,
                               bm: ast::BindingMode) -> P<ast::Pat> {
-        let pat = ast::PatIdent(bm, Spanned{span: span, node: ident}, None);
+        let pat = PatKind::Ident(bm, Spanned{span: span, node: ident}, None);
         self.pat(span, pat)
     }
     fn pat_enum(&self, span: Span, path: ast::Path, subpats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
-        let pat = ast::PatEnum(path, Some(subpats));
+        let pat = if subpats.is_empty() {
+            PatKind::Path(path)
+        } else {
+            PatKind::TupleStruct(path, Some(subpats))
+        };
         self.pat(span, pat)
     }
     fn pat_struct(&self, span: Span,
                   path: ast::Path, field_pats: Vec<Spanned<ast::FieldPat>>) -> P<ast::Pat> {
-        let pat = ast::PatStruct(path, field_pats, false);
+        let pat = PatKind::Struct(path, field_pats, false);
         self.pat(span, pat)
     }
     fn pat_tuple(&self, span: Span, pats: Vec<P<ast::Pat>>) -> P<ast::Pat> {
-        self.pat(span, ast::PatTup(pats))
+        self.pat(span, PatKind::Tup(pats))
     }
 
     fn pat_some(&self, span: Span, pat: P<ast::Pat>) -> P<ast::Pat> {