Eliminate precedence arithmetic from rustc_parse

Author: dtolnay

compiler/rustc_parse/src/parser/expr.rs

@@ -1,7 +1,7 @@
 // ignore-tidy-filelength
 
 use core::mem;
-use core::ops::ControlFlow;
+use core::ops::{Bound, ControlFlow};
 
 use ast::mut_visit::{self, MutVisitor};
 use ast::token::IdentIsRaw;
@@ -120,15 +120,15 @@ impl<'a> Parser<'a> {
         r: Restrictions,
         attrs: AttrWrapper,
     ) -> PResult<'a, (P<Expr>, bool)> {
-        self.with_res(r, |this| this.parse_expr_assoc_with(0, attrs))
+        self.with_res(r, |this| this.parse_expr_assoc_with(Bound::Unbounded, attrs))
     }
 
     /// Parses an associative expression with operators of at least `min_prec` precedence.
     /// The `bool` in the return value indicates if it was an assoc expr, i.e. with an operator
     /// followed by a subexpression (e.g. `1 + 2`).
     pub(super) fn parse_expr_assoc_with(
         &mut self,
-        min_prec: usize,
+        min_prec: Bound<usize>,
         attrs: AttrWrapper,
     ) -> PResult<'a, (P<Expr>, bool)> {
         let lhs = if self.token.is_range_separator() {
@@ -144,7 +144,7 @@ impl<'a> Parser<'a> {
     /// was actually parsed.
     pub(super) fn parse_expr_assoc_rest_with(
         &mut self,
-        min_prec: usize,
+        min_prec: Bound<usize>,
         starts_stmt: bool,
         mut lhs: P<Expr>,
     ) -> PResult<'a, (P<Expr>, bool)> {
@@ -163,7 +163,11 @@ impl<'a> Parser<'a> {
                 self.restrictions
             };
             let prec = op.node.precedence();
-            if prec < min_prec {
+            if match min_prec {
+                Bound::Included(min_prec) => prec < min_prec,
+                Bound::Excluded(min_prec) => prec <= min_prec,
+                Bound::Unbounded => false,
+            } {
                 break;
             }
             // Check for deprecated `...` syntax
@@ -276,16 +280,16 @@ impl<'a> Parser<'a> {
             }
 
             let fixity = op.fixity();
-            let prec_adjustment = match fixity {
-                Fixity::Right => 0,
-                Fixity::Left => 1,
+            let min_prec = match fixity {
+                Fixity::Right => Bound::Included(prec),
+                Fixity::Left => Bound::Excluded(prec),
                 // We currently have no non-associative operators that are not handled above by
                 // the special cases. The code is here only for future convenience.
-                Fixity::None => 1,
+                Fixity::None => Bound::Excluded(prec),
             };
             let (rhs, _) = self.with_res(restrictions - Restrictions::STMT_EXPR, |this| {
                 let attrs = this.parse_outer_attributes()?;
-                this.parse_expr_assoc_with(prec + prec_adjustment, attrs)
+                this.parse_expr_assoc_with(min_prec, attrs)
             })?;
 
             let span = self.mk_expr_sp(&lhs, lhs_span, rhs.span);
@@ -460,7 +464,7 @@ impl<'a> Parser<'a> {
             let maybe_lt = self.token.clone();
             let attrs = self.parse_outer_attributes()?;
             Some(
-                self.parse_expr_assoc_with(prec + 1, attrs)
+                self.parse_expr_assoc_with(Bound::Excluded(prec), attrs)
                     .map_err(|err| self.maybe_err_dotdotlt_syntax(maybe_lt, err))?
                     .0,
             )
@@ -518,7 +522,7 @@ impl<'a> Parser<'a> {
             let (span, opt_end) = if this.is_at_start_of_range_notation_rhs() {
                 // RHS must be parsed with more associativity than the dots.
                 let attrs = this.parse_outer_attributes()?;
-                this.parse_expr_assoc_with(op.unwrap().precedence() + 1, attrs)
+                this.parse_expr_assoc_with(Bound::Excluded(op.unwrap().precedence()), attrs)
                     .map(|(x, _)| (lo.to(x.span), Some(x)))
                     .map_err(|err| this.maybe_err_dotdotlt_syntax(maybe_lt, err))?
             } else {
@@ -2643,7 +2647,8 @@ impl<'a> Parser<'a> {
             self.expect(&token::Eq)?;
         }
         let attrs = self.parse_outer_attributes()?;
-        let (expr, _) = self.parse_expr_assoc_with(1 + prec_let_scrutinee_needs_par(), attrs)?;
+        let (expr, _) =
+            self.parse_expr_assoc_with(Bound::Excluded(prec_let_scrutinee_needs_par()), attrs)?;
         let span = lo.to(expr.span);
         Ok(self.mk_expr(span, ExprKind::Let(pat, expr, span, recovered)))
     }

compiler/rustc_parse/src/parser/pat.rs

@@ -1,3 +1,5 @@
+use std::ops::Bound;
+
 use rustc_ast::mut_visit::{self, MutVisitor};
 use rustc_ast::ptr::P;
 use rustc_ast::token::{self, BinOpToken, Delimiter, IdentIsRaw, Token};
@@ -435,8 +437,9 @@ impl<'a> Parser<'a> {
 
         // Parse an associative expression such as `+ expr`, `% expr`, ...
         // Assignments, ranges and `|` are disabled by [`Restrictions::IS_PAT`].
-        let Ok((expr, _)) =
-            snapshot.parse_expr_assoc_rest_with(0, false, expr).map_err(|err| err.cancel())
+        let Ok((expr, _)) = snapshot
+            .parse_expr_assoc_rest_with(Bound::Unbounded, false, expr)
+            .map_err(|err| err.cancel())
         else {
             // We got a trailing method/operator, but that wasn't an expression.
             return None;

compiler/rustc_parse/src/parser/stmt.rs

@@ -1,5 +1,6 @@
 use std::borrow::Cow;
 use std::mem;
+use std::ops::Bound;
 
 use ast::Label;
 use rustc_ast as ast;
@@ -207,7 +208,7 @@ impl<'a> Parser<'a> {
             // Perform this outside of the `collect_tokens` closure, since our
             // outer attributes do not apply to this part of the expression.
             let (expr, _) = self.with_res(Restrictions::STMT_EXPR, |this| {
-                this.parse_expr_assoc_rest_with(0, true, expr)
+                this.parse_expr_assoc_rest_with(Bound::Unbounded, true, expr)
             })?;
             Ok(self.mk_stmt(lo.to(self.prev_token.span), StmtKind::Expr(expr)))
         } else {
@@ -240,7 +241,7 @@ impl<'a> Parser<'a> {
             let e = self.mk_expr(lo.to(hi), ExprKind::MacCall(mac));
             let e = self.maybe_recover_from_bad_qpath(e)?;
             let e = self.parse_expr_dot_or_call_with(attrs, e, lo)?;
-            let (e, _) = self.parse_expr_assoc_rest_with(0, false, e)?;
+            let (e, _) = self.parse_expr_assoc_rest_with(Bound::Unbounded, false, e)?;
             StmtKind::Expr(e)
         };
         Ok(self.mk_stmt(lo.to(hi), kind))