[RFC-2011] Expand matches!

compiler/rustc_ast/src/ast.rs

@@ -1291,6 +1291,7 @@ impl Expr {
             ExprKind::Struct(..) => ExprPrecedence::Struct,
             ExprKind::Repeat(..) => ExprPrecedence::Repeat,
             ExprKind::Paren(..) => ExprPrecedence::Paren,
+            ExprKind::Matches(..) => ExprPrecedence::Matches,
             ExprKind::Try(..) => ExprPrecedence::Try,
             ExprKind::Yield(..) => ExprPrecedence::Yield,
             ExprKind::Yeet(..) => ExprPrecedence::Yeet,
@@ -1488,6 +1489,9 @@ pub enum ExprKind {
     /// Output of the `offset_of!()` macro.
     OffsetOf(P<Ty>, P<[Ident]>),
 
+    /// Output of the `matches!()` macro.
+    Matches(P<Expr>, P<Arm>, P<Arm>),
+
     /// A macro invocation; pre-expansion.
     MacCall(P<MacCall>),
 

compiler/rustc_ast/src/mut_visit.rs

@@ -148,6 +148,10 @@ pub trait MutVisitor: Sized {
         noop_visit_anon_const(c, self);
     }
 
+    fn visit_arm(&mut self, arm: &mut P<Arm>) {
+        noop_visit_arm(arm, self)
+    }
+
     fn visit_expr(&mut self, e: &mut P<Expr>) {
         noop_visit_expr(e, self);
     }
@@ -443,13 +447,7 @@ pub fn noop_visit_use_tree<T: MutVisitor>(use_tree: &mut UseTree, vis: &mut T) {
 }
 
 pub fn noop_flat_map_arm<T: MutVisitor>(mut arm: Arm, vis: &mut T) -> SmallVec<[Arm; 1]> {
-    let Arm { attrs, pat, guard, body, span, id, is_placeholder: _ } = &mut arm;
-    visit_attrs(attrs, vis);
-    vis.visit_id(id);
-    vis.visit_pat(pat);
-    visit_opt(guard, |guard| vis.visit_expr(guard));
-    vis.visit_expr(body);
-    vis.visit_span(span);
+    noop_visit_arm(&mut arm, vis);
     smallvec![arm]
 }
 
@@ -695,6 +693,16 @@ pub fn visit_attr_tt<T: MutVisitor>(tt: &mut AttrTokenTree, vis: &mut T) {
     }
 }
 
+fn noop_visit_arm<T: MutVisitor>(arm: &mut Arm, vis: &mut T) {
+    let Arm { attrs, pat, guard, body, span, id, is_placeholder: _ } = arm;
+    visit_attrs(attrs, vis);
+    vis.visit_id(id);
+    vis.visit_pat(pat);
+    visit_opt(guard, |guard| vis.visit_expr(guard));
+    vis.visit_expr(body);
+    vis.visit_span(span);
+}
+
 // No `noop_` prefix because there isn't a corresponding method in `MutVisitor`.
 pub fn visit_tt<T: MutVisitor>(tt: &mut TokenTree, vis: &mut T) {
     match tt {
@@ -1334,6 +1342,11 @@ pub fn noop_visit_expr<T: MutVisitor>(
             vis.visit_expr(f);
             visit_thin_exprs(args, vis);
         }
+        ExprKind::Matches(expr, true_arm, false_arm) => {
+            vis.visit_expr(expr);
+            vis.visit_arm(true_arm);
+            vis.visit_arm(false_arm);
+        }
         ExprKind::MethodCall(box MethodCall {
             seg: PathSegment { ident, id, args: seg_args },
             receiver,

compiler/rustc_ast/src/util/parser.rs

@@ -267,6 +267,7 @@ pub enum ExprPrecedence {
     InlineAsm,
     OffsetOf,
     Mac,
+    Matches,
     FormatArgs,
 
     Array,
@@ -329,6 +330,7 @@ impl ExprPrecedence {
             | ExprPrecedence::Field
             | ExprPrecedence::Index
             | ExprPrecedence::Try
+            | ExprPrecedence::Matches
             | ExprPrecedence::InlineAsm
             | ExprPrecedence::Mac
             | ExprPrecedence::FormatArgs

compiler/rustc_ast/src/visit.rs

@@ -803,6 +803,11 @@ pub fn walk_expr<'a, V: Visitor<'a>>(visitor: &mut V, expression: &'a Expr) {
             visitor.visit_expr(callee_expression);
             walk_list!(visitor, visit_expr, arguments);
         }
+        ExprKind::Matches(expr, true_arm, false_arm) => {
+            visitor.visit_expr(expr);
+            visitor.visit_arm(true_arm);
+            visitor.visit_arm(false_arm);
+        }
         ExprKind::MethodCall(box MethodCall { seg, receiver, args, span: _ }) => {
             visitor.visit_path_segment(seg);
             visitor.visit_expr(receiver);

compiler/rustc_ast_lowering/src/expr.rs

@@ -274,6 +274,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::InlineAsm(asm) => {
                     hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))
                 }
+                ExprKind::Matches(expr, true_arm, false_arm) => hir::ExprKind::Match(
+                    self.lower_expr(expr),
+                    self.arena.alloc_from_iter(
+                        [true_arm, false_arm].iter().map(|elem| self.lower_arm(elem)),
+                    ),
+                    hir::MatchSource::Normal,
+                ),
                 ExprKind::FormatArgs(fmt) => self.lower_format_args(e.span, fmt),
                 ExprKind::OffsetOf(container, fields) => hir::ExprKind::OffsetOf(
                     self.lower_ty(

compiler/rustc_ast_pretty/src/pprust/state/expr.rs

@@ -555,6 +555,20 @@ impl<'a> State<'a> {
                 self.end();
                 self.pclose();
             }
+            ast::ExprKind::Matches(expr, true_arm, _) => {
+                self.word("builtin # matches");
+                self.popen();
+                self.rbox(0, Inconsistent);
+                self.print_expr(expr);
+                self.word(", ");
+                self.print_pat(&true_arm.pat);
+                if let Some(elem) = &true_arm.guard {
+                    self.word("if");
+                    self.print_expr(elem);
+                }
+                self.pclose();
+                self.end();
+            }
             ast::ExprKind::OffsetOf(container, fields) => {
                 self.word("builtin # offset_of");
                 self.popen();

compiler/rustc_builtin_macros/src/assert.rs

@@ -31,31 +31,13 @@ pub fn expand_assert<'cx>(
     // context to pick up whichever is currently in scope.
     let call_site_span = cx.with_call_site_ctxt(span);
 
-    let panic_path = || {
-        if use_panic_2021(span) {
-            // On edition 2021, we always call `$crate::panic::panic_2021!()`.
-            Path {
-                span: call_site_span,
-                segments: cx
-                    .std_path(&[sym::panic, sym::panic_2021])
-                    .into_iter()
-                    .map(|ident| PathSegment::from_ident(ident))
-                    .collect(),
-                tokens: None,
-            }
-        } else {
-            // Before edition 2021, we call `panic!()` unqualified,
-            // such that it calls either `std::panic!()` or `core::panic!()`.
-            Path::from_ident(Ident::new(sym::panic, call_site_span))
-        }
-    };
-
     // Simply uses the user provided message instead of generating custom outputs
     let expr = if let Some(tokens) = custom_message {
+        let panic_path = panic_path(call_site_span, cx, span);
         let then = cx.expr(
             call_site_span,
             ExprKind::MacCall(P(MacCall {
-                path: panic_path(),
+                path: panic_path,
                 args: P(DelimArgs {
                     dspan: DelimSpan::from_single(call_site_span),
                     delim: MacDelimiter::Parenthesis,
@@ -69,7 +51,8 @@ pub fn expand_assert<'cx>(
     //
     // FIXME(c410-f3r) See https://github.com/rust-lang/rust/issues/96949
     else if let Some(features) = cx.ecfg.features && features.generic_assert {
-        context::Context::new(cx, call_site_span).build(cond_expr, panic_path())
+        let panic_path = panic_path(call_site_span, cx, span);
+        context::Context::new(cx, call_site_span).build(cond_expr, panic_path)
     }
     // If `generic_assert` is not enabled, only outputs a literal "assertion failed: ..."
     // string
@@ -110,6 +93,25 @@ fn expr_if_not(
     cx.expr_if(span, cx.expr(span, ExprKind::Unary(UnOp::Not, cond)), then, els)
 }
 
+fn panic_path(call_site_span: Span, cx: &mut ExtCtxt<'_>, span: Span) -> Path {
+    if use_panic_2021(span) {
+        // On edition 2021, we always call `$crate::panic::panic_2021!()`.
+        Path {
+            span: call_site_span,
+            segments: cx
+                .std_path(&[sym::panic, sym::panic_2021])
+                .into_iter()
+                .map(|ident| PathSegment::from_ident(ident))
+                .collect(),
+            tokens: None,
+        }
+    } else {
+        // Before edition 2021, we call `panic!()` unqualified,
+        // such that it calls either `std::panic!()` or `core::panic!()`.
+        Path::from_ident(Ident::new(sym::panic, call_site_span))
+    }
+}
+
 fn parse_assert<'a>(cx: &mut ExtCtxt<'a>, sp: Span, stream: TokenStream) -> PResult<'a, Assert> {
     let mut parser = cx.new_parser_from_tts(stream);
 

compiler/rustc_builtin_macros/src/assert/context.rs

@@ -22,7 +22,7 @@ pub(super) struct Context<'cx, 'a> {
     best_case_captures: Vec<Stmt>,
     // Top-level `let captureN = Capture::new()` statements
     capture_decls: Vec<Capture>,
-    cx: &'cx ExtCtxt<'a>,
+    cx: &'cx mut ExtCtxt<'a>,
     // Formatting string used for debugging
     fmt_string: String,
     // If the current expression being visited consumes itself. Used to construct
@@ -41,7 +41,7 @@ pub(super) struct Context<'cx, 'a> {
 }
 
 impl<'cx, 'a> Context<'cx, 'a> {
-    pub(super) fn new(cx: &'cx ExtCtxt<'a>, span: Span) -> Self {
+    pub(super) fn new(cx: &'cx mut ExtCtxt<'a>, span: Span) -> Self {
         Self {
             best_case_captures: <_>::default(),
             capture_decls: <_>::default(),
@@ -85,8 +85,8 @@ impl<'cx, 'a> Context<'cx, 'a> {
 
         let mut assert_then_stmts = ThinVec::with_capacity(2);
         assert_then_stmts.extend(best_case_captures);
-        assert_then_stmts.push(self.cx.stmt_expr(panic));
-        let assert_then = self.cx.block(span, assert_then_stmts);
+        assert_then_stmts.push(cx.stmt_expr(panic));
+        let assert_then = cx.block(span, assert_then_stmts);
 
         let mut stmts = ThinVec::with_capacity(4);
         stmts.push(initial_imports);
@@ -237,6 +237,9 @@ impl<'cx, 'a> Context<'cx, 'a> {
                 self.manage_cond_expr(prefix);
                 self.manage_cond_expr(suffix);
             }
+            ExprKind::Matches(expr, _, _) => {
+                self.manage_cond_expr(expr);
+            }
             ExprKind::MethodCall(call) => {
                 for arg in &mut call.args {
                     self.manage_cond_expr(arg);
@@ -295,17 +298,17 @@ impl<'cx, 'a> Context<'cx, 'a> {
             | ExprKind::Continue(_)
             | ExprKind::Err
             | ExprKind::Field(_, _)
-            | ExprKind::FormatArgs(_)
             | ExprKind::ForLoop(_, _, _, _)
+            | ExprKind::FormatArgs(_)
             | ExprKind::If(_, _, _)
             | ExprKind::IncludedBytes(..)
             | ExprKind::InlineAsm(_)
-            | ExprKind::OffsetOf(_, _)
             | ExprKind::Let(_, _, _)
             | ExprKind::Lit(_)
             | ExprKind::Loop(_, _, _)
             | ExprKind::MacCall(_)
             | ExprKind::Match(_, _)
+            | ExprKind::OffsetOf(_, _)
             | ExprKind::Path(_, _)
             | ExprKind::Ret(_)
             | ExprKind::Try(_)