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rollup merge of #20726: dgrunwald/require-parens-for-chained-comparison

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[Rendered RFC](https://github.com/rust-lang/rfcs/blob/master/text/0558-require-parentheses-for-chained-comparisons.md)
This commit is contained in:
Alex Crichton 2015-01-07 17:19:55 -08:00
commit f6a7dc5528
4 changed files with 58 additions and 4 deletions
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24
src/libsyntax/parse/parser.rs
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@ -16,7 +16,7 @@ use ast::{AssociatedType, BareFnTy};
use ast::{RegionTyParamBound, TraitTyParamBound, TraitBoundModifier};
use ast::{ProvidedMethod, Public, Unsafety};
use ast::{Mod, BiAdd, Arg, Arm, Attribute, BindByRef, BindByValue};
use ast::{BiBitAnd, BiBitOr, BiBitXor, BiRem, Block};
use ast::{BiBitAnd, BiBitOr, BiBitXor, BiRem, BiLt, BiGt, Block};
use ast::{BlockCheckMode, CaptureByRef, CaptureByValue, CaptureClause};
use ast::{Crate, CrateConfig, Decl, DeclItem};
use ast::{DeclLocal, DefaultBlock, UnDeref, BiDiv, EMPTY_CTXT, EnumDef, ExplicitSelf};
@ -2906,6 +2906,9 @@ impl<'a> Parser<'a> {
let cur_opt = self.token.to_binop();
match cur_opt {
Some(cur_op) => {
if ast_util::is_comparison_binop(cur_op) {
self.check_no_chained_comparison(&*lhs, cur_op)
}
let cur_prec = operator_prec(cur_op);
if cur_prec > min_prec {
self.bump();
@ -2934,6 +2937,25 @@ impl<'a> Parser<'a> {
}
}
/// Produce an error if comparison operators are chained (RFC #558).
/// We only need to check lhs, not rhs, because all comparison ops
/// have same precedence and are left-associative
fn check_no_chained_comparison(&mut self, lhs: &Expr, outer_op: ast::BinOp) {
debug_assert!(ast_util::is_comparison_binop(outer_op));
match lhs.node {
ExprBinary(op, _, _) if ast_util::is_comparison_binop(op) => {
let op_span = self.span;
self.span_err(op_span,
"Chained comparison operators require parentheses");
if op == BiLt && outer_op == BiGt {
self.span_help(op_span,
"Use ::< instead of < if you meant to specify type arguments.");
}
}
_ => {}
}
}
/// Parse an assignment expression....
/// actually, this seems to be the main entry point for
/// parsing an arbitrary expression.