view-types: store borrows of view types in the AST

Author: scrabsha

compiler/rustc_ast/src/ast.rs

@@ -646,8 +646,10 @@ impl Pat {
             PatKind::MacCall(mac) => TyKind::MacCall(mac.clone()),
             // `&mut? P` can be reinterpreted as `&mut? T` where `T` is `P` reparsed as a type.
             PatKind::Ref(pat, pinned, mutbl) => pat.to_ty().map(|ty| match pinned {
-                Pinnedness::Not => TyKind::Ref(None, MutTy { ty, mutbl: *mutbl }),
-                Pinnedness::Pinned => TyKind::PinnedRef(None, MutTy { ty, mutbl: *mutbl }),
+                Pinnedness::Not => TyKind::Ref(None, MutTy { ty, mutbl: *mutbl }, ViewKind::Full),
+                Pinnedness::Pinned => {
+                    TyKind::PinnedRef(None, MutTy { ty, mutbl: *mutbl }, ViewKind::Full)
+                }
             })?,
             // A slice/array pattern `[P]` can be reparsed as `[T]`, an unsized array,
             // when `P` can be reparsed as a type `T`.
@@ -1510,9 +1512,9 @@ impl Expr {
 
             ExprKind::Paren(expr) => expr.to_ty().map(TyKind::Paren)?,
 
-            ExprKind::AddrOf(BorrowKind::Ref, mutbl, expr) => {
-                expr.to_ty().map(|ty| TyKind::Ref(None, MutTy { ty, mutbl: *mutbl }))?
-            }
+            ExprKind::AddrOf(BorrowKind::Ref, mutbl, expr) => expr
+                .to_ty()
+                .map(|ty| TyKind::Ref(None, MutTy { ty, mutbl: *mutbl }, ViewKind::Full))?,
 
             ExprKind::Repeat(expr, expr_len) => {
                 expr.to_ty().map(|ty| TyKind::Array(ty, expr_len.clone()))?
@@ -2473,7 +2475,8 @@ impl From<Box<Ty>> for Ty {
 impl Ty {
     pub fn peel_refs(&self) -> &Self {
         let mut final_ty = self;
-        while let TyKind::Ref(_, MutTy { ty, .. }) | TyKind::Ptr(MutTy { ty, .. }) = &final_ty.kind
+        while let TyKind::Ref(_, MutTy { ty, .. }, _) | TyKind::Ptr(MutTy { ty, .. }) =
+            &final_ty.kind
         {
             final_ty = ty;
         }
@@ -2518,11 +2521,11 @@ pub enum TyKind {
     /// A raw pointer (`*const T` or `*mut T`).
     Ptr(MutTy),
     /// A reference (`&'a T` or `&'a mut T`).
-    Ref(#[visitable(extra = LifetimeCtxt::Ref)] Option<Lifetime>, MutTy),
+    Ref(#[visitable(extra = LifetimeCtxt::Ref)] Option<Lifetime>, MutTy, ViewKind),
     /// A pinned reference (`&'a pin const T` or `&'a pin mut T`).
     ///
     /// Desugars into `Pin<&'a T>` or `Pin<&'a mut T>`.
-    PinnedRef(#[visitable(extra = LifetimeCtxt::Ref)] Option<Lifetime>, MutTy),
+    PinnedRef(#[visitable(extra = LifetimeCtxt::Ref)] Option<Lifetime>, MutTy, ViewKind),
     /// A function pointer type (e.g., `fn(usize) -> bool`).
     FnPtr(Box<FnPtrTy>),
     /// An unsafe existential lifetime binder (e.g., `unsafe<'a> &'a ()`).
@@ -2660,6 +2663,21 @@ pub enum TraitObjectSyntax {
     None = 1,
 }
 
+/// Represents how a reference is viewed.
+// FIXME(scrabsha): move this to a new variant of `Mutabiliy` when viewing of non-reference types
+// is implemented.
+#[derive(Clone, Encodable, Decodable, Debug, Walkable)]
+pub enum ViewKind {
+    /// `&mut T`. All the fields can be observed.
+    Full,
+    /// `&mut T.{ foo, bar }`. Only `foo` and `bar` can be observed.
+    Partial {
+        span: Span,
+        #[visitable(ignore)]
+        fields: ThinVec<Ident>,
+    },
+}
+
 /// SAFETY: `TraitObjectSyntax` only has 3 data-less variants which means
 /// it can be represented with a `u2`. We use `repr(u8)` to guarantee the
 /// discriminants of the variants are no greater than `3`.
@@ -2933,21 +2951,21 @@ pub struct Param {
 pub enum SelfKind {
     /// `self`, `mut self`
     Value(Mutability),
-    /// `&'lt self`, `&'lt mut self`
-    Region(Option<Lifetime>, Mutability),
-    /// `&'lt pin const self`, `&'lt pin mut self`
-    Pinned(Option<Lifetime>, Mutability),
+    /// `&'lt self`, `&'lt mut self`, `&'lt mut self.{ a, b }`
+    Region(Option<Lifetime>, Mutability, ViewKind),
+    /// `&'lt pin const self`, `&'lt pin mut self`, `&'lt pin mut self.{ a, b }`.
+    Pinned(Option<Lifetime>, Mutability, ViewKind),
     /// `self: TYPE`, `mut self: TYPE`
     Explicit(Box<Ty>, Mutability),
 }
 
 impl SelfKind {
     pub fn to_ref_suggestion(&self) -> String {
         match self {
-            SelfKind::Region(None, mutbl) => mutbl.ref_prefix_str().to_string(),
-            SelfKind::Region(Some(lt), mutbl) => format!("&{lt} {}", mutbl.prefix_str()),
-            SelfKind::Pinned(None, mutbl) => format!("&pin {}", mutbl.ptr_str()),
-            SelfKind::Pinned(Some(lt), mutbl) => format!("&{lt} pin {}", mutbl.ptr_str()),
+            SelfKind::Region(None, mutbl, _) => mutbl.ref_prefix_str().to_string(),
+            SelfKind::Region(Some(lt), mutbl, _) => format!("&{lt} {}", mutbl.prefix_str()),
+            SelfKind::Pinned(None, mutbl, _) => format!("&pin {}", mutbl.ptr_str()),
+            SelfKind::Pinned(Some(lt), mutbl, _) => format!("&{lt} pin {}", mutbl.ptr_str()),
             SelfKind::Value(_) | SelfKind::Explicit(_, _) => {
                 unreachable!("if we had an explicit self, we wouldn't be here")
             }
@@ -2964,13 +2982,15 @@ impl Param {
             if ident.name == kw::SelfLower {
                 return match self.ty.kind {
                     TyKind::ImplicitSelf => Some(respan(self.pat.span, SelfKind::Value(mutbl))),
-                    TyKind::Ref(lt, MutTy { ref ty, mutbl }) if ty.kind.is_implicit_self() => {
-                        Some(respan(self.pat.span, SelfKind::Region(lt, mutbl)))
+                    TyKind::Ref(lt, MutTy { ref ty, mutbl }, ref view)
+                        if ty.kind.is_implicit_self() =>
+                    {
+                        Some(respan(self.pat.span, SelfKind::Region(lt, mutbl, view.clone())))
                     }
-                    TyKind::PinnedRef(lt, MutTy { ref ty, mutbl })
+                    TyKind::PinnedRef(lt, MutTy { ref ty, mutbl }, ref view)
                         if ty.kind.is_implicit_self() =>
                     {
-                        Some(respan(self.pat.span, SelfKind::Pinned(lt, mutbl)))
+                        Some(respan(self.pat.span, SelfKind::Pinned(lt, mutbl, view.clone())))
                     }
                     _ => Some(respan(
                         self.pat.span.to(self.ty.span),
@@ -3003,20 +3023,20 @@ impl Param {
         let (mutbl, ty) = match eself.node {
             SelfKind::Explicit(ty, mutbl) => (mutbl, ty),
             SelfKind::Value(mutbl) => (mutbl, infer_ty),
-            SelfKind::Region(lt, mutbl) => (
+            SelfKind::Region(lt, mutbl, views) => (
                 Mutability::Not,
                 Box::new(Ty {
                     id: DUMMY_NODE_ID,
-                    kind: TyKind::Ref(lt, MutTy { ty: infer_ty, mutbl }),
+                    kind: TyKind::Ref(lt, MutTy { ty: infer_ty, mutbl }, views),
                     span,
                     tokens: None,
                 }),
             ),
-            SelfKind::Pinned(lt, mutbl) => (
+            SelfKind::Pinned(lt, mutbl, view) => (
                 mutbl,
                 Box::new(Ty {
                     id: DUMMY_NODE_ID,
-                    kind: TyKind::PinnedRef(lt, MutTy { ty: infer_ty, mutbl }),
+                    kind: TyKind::PinnedRef(lt, MutTy { ty: infer_ty, mutbl }, view),
                     span,
                     tokens: None,
                 }),
@@ -4340,7 +4360,7 @@ mod size_asserts {
     static_assert_size!(Stmt, 32);
     static_assert_size!(StmtKind, 16);
     static_assert_size!(TraitImplHeader, 72);
-    static_assert_size!(Ty, 64);
-    static_assert_size!(TyKind, 40);
+    static_assert_size!(Ty, 80);
+    static_assert_size!(TyKind, 56);
     // tidy-alphabetical-end
 }

compiler/rustc_ast/src/util/classify.rs

@@ -1,5 +1,6 @@
 //! Routines the parser and pretty-printer use to classify AST nodes.
 
+use crate::ViewKind;
 use crate::ast::ExprKind::*;
 use crate::ast::{self, MatchKind};
 use crate::token::Delimiter;
@@ -167,6 +168,8 @@ pub enum TrailingBrace<'a> {
     /// Trailing brace in any other expression, such as `a + B {}`. We will
     /// suggest wrapping the innermost expression in parentheses: `a + (B {})`.
     Expr(&'a ast::Expr),
+    /// Trailing brace in a type, like the one in `&Foo. { bar }`
+    Type(&'a ast::Ty),
 }
 
 /// If an expression ends with `}`, returns the innermost expression ending in the `}`
@@ -205,7 +208,7 @@ pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<TrailingBrace<'_>> {
             | ConstBlock(_) => break Some(TrailingBrace::Expr(expr)),
 
             Cast(_, ty) => {
-                break type_trailing_braced_mac_call(ty).map(TrailingBrace::MacCall);
+                break type_trailing_brace(ty);
             }
 
             MacCall(mac) => {
@@ -246,21 +249,30 @@ pub fn expr_trailing_brace(mut expr: &ast::Expr) -> Option<TrailingBrace<'_>> {
     }
 }
 
-/// If the type's last token is `}`, it must be due to a braced macro call, such
-/// as in `*const brace! { ... }`. Returns that trailing macro call.
-fn type_trailing_braced_mac_call(mut ty: &ast::Ty) -> Option<&ast::MacCall> {
+/// If a type ends with `}`, return the innermost node ending with the `}`.
+///
+/// This may be caused by a macro call (`*const brace! { ... }`) or a view type
+/// (`&Foo.{ bar }`).
+fn type_trailing_brace(mut ty: &ast::Ty) -> Option<TrailingBrace<'_>> {
     loop {
         match &ty.kind {
             ast::TyKind::MacCall(mac) => {
-                break (mac.args.delim == Delimiter::Brace).then_some(mac);
+                break (mac.args.delim == Delimiter::Brace)
+                    .then_some(mac.as_ref())
+                    .map(TrailingBrace::MacCall);
             }
 
             ast::TyKind::Ptr(mut_ty)
-            | ast::TyKind::Ref(_, mut_ty)
-            | ast::TyKind::PinnedRef(_, mut_ty) => {
+            | ast::TyKind::Ref(_, mut_ty, ViewKind::Full)
+            | ast::TyKind::PinnedRef(_, mut_ty, ViewKind::Full) => {
                 ty = &mut_ty.ty;
             }
 
+            ast::TyKind::Ref(_, _, ViewKind::Partial { .. })
+            | ast::TyKind::PinnedRef(_, _, ViewKind::Partial { .. }) => {
+                break Some(TrailingBrace::Type(ty));
+            }
+
             ast::TyKind::UnsafeBinder(binder) => {
                 ty = &binder.inner_ty;
             }

compiler/rustc_ast/src/visit.rs

@@ -486,6 +486,7 @@ macro_rules! common_visitor_and_walkers {
             UnsafeBinderTy,
             UnsafeSource,
             UseTreeKind,
+            ViewKind,
             VisibilityKind,
             WhereBoundPredicate,
             WhereClause,

compiler/rustc_ast_lowering/src/lib.rs

@@ -1413,11 +1413,11 @@ impl<'hir> LoweringContext<'_, 'hir> {
             TyKind::Err(guar) => hir::TyKind::Err(*guar),
             TyKind::Slice(ty) => hir::TyKind::Slice(self.lower_ty_alloc(ty, itctx)),
             TyKind::Ptr(mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
-            TyKind::Ref(region, mt) => {
+            TyKind::Ref(region, mt, _) => {
                 let lifetime = self.lower_ty_direct_lifetime(t, *region);
                 hir::TyKind::Ref(lifetime, self.lower_mt(mt, itctx))
             }
-            TyKind::PinnedRef(region, mt) => {
+            TyKind::PinnedRef(region, mt, _) => {
                 let lifetime = self.lower_ty_direct_lifetime(t, *region);
                 let kind = hir::TyKind::Ref(lifetime, self.lower_mt(mt, itctx));
                 let span = self.lower_span(t.span);
@@ -1841,7 +1841,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                     // Given we are only considering `ImplicitSelf` types, we needn't consider
                     // the case where we have a mutable pattern to a reference as that would
                     // no longer be an `ImplicitSelf`.
-                    TyKind::Ref(_, mt) | TyKind::PinnedRef(_, mt)
+                    TyKind::Ref(_, mt, _) | TyKind::PinnedRef(_, mt, _)
                         if mt.ty.kind.is_implicit_self() =>
                     {
                         match mt.mutbl {

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -17,7 +17,7 @@ use rustc_ast::util::comments::{Comment, CommentStyle};
 use rustc_ast::{
     self as ast, AttrArgs, BindingMode, BlockCheckMode, ByRef, DelimArgs, GenericArg, GenericBound,
     InlineAsmOperand, InlineAsmOptions, InlineAsmRegOrRegClass, InlineAsmTemplatePiece, PatKind,
-    RangeEnd, RangeSyntax, Safety, SelfKind, Term, attr,
+    RangeEnd, RangeSyntax, Safety, SelfKind, Term, ViewKind, attr,
 };
 use rustc_span::edition::Edition;
 use rustc_span::source_map::SourceMap;
@@ -1255,6 +1255,16 @@ impl<'a> State<'a> {
         }
     }
 
+    fn print_view(&mut self, view: &ViewKind) {
+        if let ViewKind::Partial { fields, .. } = view {
+            self.word_space(".{");
+            self.commasep(Breaks::Inconsistent, fields, |s, field| {
+                s.print_ident(*field);
+            });
+            self.word_space(" }");
+        }
+    }
+
     pub fn print_assoc_item_constraint(&mut self, constraint: &ast::AssocItemConstraint) {
         self.print_ident(constraint.ident);
         if let Some(args) = constraint.gen_args.as_ref() {
@@ -1333,16 +1343,18 @@ impl<'a> State<'a> {
                 self.word("*");
                 self.print_mt(mt, true);
             }
-            ast::TyKind::Ref(lifetime, mt) => {
+            ast::TyKind::Ref(lifetime, mt, view) => {
                 self.word("&");
                 self.print_opt_lifetime(lifetime);
                 self.print_mt(mt, false);
+                self.print_view(view);
             }
-            ast::TyKind::PinnedRef(lifetime, mt) => {
+            ast::TyKind::PinnedRef(lifetime, mt, view) => {
                 self.word("&");
                 self.print_opt_lifetime(lifetime);
                 self.word("pin ");
                 self.print_mt(mt, true);
+                self.print_view(view);
             }
             ast::TyKind::Never => {
                 self.word("!");
@@ -2056,26 +2068,28 @@ impl<'a> State<'a> {
         match &explicit_self.node {
             SelfKind::Value(m) => {
                 self.print_mutability(*m, false);
-                self.word("self")
+                self.word("self");
             }
-            SelfKind::Region(lt, m) => {
+            SelfKind::Region(lt, m, view) => {
                 self.word("&");
                 self.print_opt_lifetime(lt);
                 self.print_mutability(*m, false);
-                self.word("self")
+                self.word("self");
+                self.print_view(view);
             }
-            SelfKind::Pinned(lt, m) => {
+            SelfKind::Pinned(lt, m, view) => {
                 self.word("&");
                 self.print_opt_lifetime(lt);
                 self.word("pin ");
                 self.print_mutability(*m, true);
-                self.word("self")
+                self.word("self");
+                self.print_view(view);
             }
             SelfKind::Explicit(typ, m) => {
                 self.print_mutability(*m, false);
                 self.word("self");
                 self.word_space(":");
-                self.print_type(typ)
+                self.print_type(typ);
             }
         }
     }

compiler/rustc_ast_pretty/src/pprust/tests.rs

@@ -22,6 +22,12 @@ fn variant_to_string(var: &ast::Variant) -> String {
     to_string(|s| s.print_variant(var))
 }
 
+fn ty_to_string(ty: &ast::Ty) -> String {
+    to_string(|s| {
+        s.print_type(ty);
+    })
+}
+
 #[test]
 fn test_fun_to_string() {
     create_default_session_globals_then(|| {
@@ -60,3 +66,36 @@ fn test_variant_to_string() {
         assert_eq!(varstr, "principal_skinner");
     })
 }
+
+#[test]
+fn test_field_view() {
+    create_default_session_globals_then(|| {
+        let ty = ast::Ty {
+            id: ast::DUMMY_NODE_ID,
+            kind: ast::TyKind::Ref(
+                None,
+                ast::MutTy {
+                    ty: Box::new(ast::Ty {
+                        id: ast::DUMMY_NODE_ID,
+                        kind: ast::TyKind::Dummy,
+                        span: DUMMY_SP,
+                        tokens: None,
+                    }),
+                    mutbl: ast::Mutability::Mut,
+                },
+                ast::ViewKind::Partial {
+                    span: DUMMY_SP,
+                    fields: thin_vec::thin_vec![
+                        Ident::from_str("milhouse"),
+                        Ident::from_str("apu")
+                    ],
+                },
+            ),
+            span: DUMMY_SP,
+            tokens: None,
+        };
+
+        let ty_str = ty_to_string(&ty);
+        assert_eq!(ty_str, "&mut (/*DUMMY*/).{ milhouse, apu }");
+    });
+}