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Added warning/error for if-let-chain ambiguity.
With eRFC 2497, previously accepted ambigious syntax regarding use of `&&` and `||` in if-let and while-let statements should now warn or error depending on the edition. This commit takes a naive approach to detecting ambigious use of `&&` or `||` and will probably need fine tuned to handle all cases.
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‎src/libsyntax/parse/parser.rs

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@@ -3327,6 +3327,8 @@ impl<'a> Parser<'a> {
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let pats = self.parse_pats()?;
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self.expect(&token::Eq)?;
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let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
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self.while_if_let_ambiguity(&expr);
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let thn = self.parse_block()?;
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let (hi, els) = if self.eat_keyword(keywords::Else) {
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let expr = self.parse_else_expr()?;
@@ -3337,6 +3339,56 @@ impl<'a> Parser<'a> {
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Ok(self.mk_expr(lo.to(hi), ExprKind::IfLet(pats, expr, thn, els), attrs))
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}
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3342+
/// With eRFC 2497, we need to check whether an expression is ambigious and warn or error
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/// depending on the edition, this function handles that.
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fn while_if_let_ambiguity(&self, expr: &P<Expr>) {
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if let Some((span, op_kind)) = self.while_if_let_expr_ambiguity(&expr) {
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let message = format!("ambigious use of `{}`", op_kind.to_string());
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let mut err = if self.span.edition() >= Edition::Edition2018 {
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self.diagnostic().struct_span_err(span, &message)
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} else {
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self.diagnostic().struct_span_warn(span, &message)
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};
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let note = if self.span.edition() >= Edition::Edition2018 {
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"This will be a error until the `let_chains` feature is stabilized."
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} else {
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"This will be a error in Rust 2018 until the `let_chains` feature is stabilized."
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};
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err.note(note);
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if let Ok(snippet) = self.sess.source_map().span_to_snippet(span) {
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err.span_suggestion(
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span, "consider adding parenthesis", format!("({})", snippet),
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);
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}
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err.emit();
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}
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}
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/// With eRFC 2497 adding if-let chains, there is a requirement that the parsing of
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/// `&&` and `||` in a if-let statement be unambigious. This function returns a span and
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/// a `BinOpKind` (either `&&` or `||` depending on what was ambigious) if it is determined
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/// that the current expression parsed is ambigious and will break in future.
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fn while_if_let_expr_ambiguity(&self, expr: &P<Expr>) -> Option<(Span, BinOpKind)> {
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debug!("while_if_let_expr_ambiguity: expr.node: {:?}", expr.node);
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match &expr.node {
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ExprKind::Binary(op, _, _) if op.node == BinOpKind::And || op.node == BinOpKind::Or => {
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Some((expr.span, op.node))
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},
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ExprKind::Range(ref lhs, ref rhs, _) => {
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let lhs_ambigious = lhs.as_ref()
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.and_then(|lhs| self.while_if_let_expr_ambiguity(lhs));
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let rhs_ambigious = rhs.as_ref()
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.and_then(|rhs| self.while_if_let_expr_ambiguity(rhs));
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lhs_ambigious.or(rhs_ambigious)
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}
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_ => None,
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}
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}
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// `move |args| expr`
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fn parse_lambda_expr(&mut self,
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attrs: ThinVec<Attribute>)
@@ -3437,6 +3489,7 @@ impl<'a> Parser<'a> {
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let pats = self.parse_pats()?;
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self.expect(&token::Eq)?;
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let expr = self.parse_expr_res(Restrictions::NO_STRUCT_LITERAL, None)?;
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self.while_if_let_ambiguity(&expr);
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let (iattrs, body) = self.parse_inner_attrs_and_block()?;
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attrs.extend(iattrs);
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let span = span_lo.to(body.span);

‎src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.rs

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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// edition:2015
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// compile-pass
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// Enabling `ireffutable_let_patterns` isn't necessary for what this tests, but it makes coming up
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// with examples easier.
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#![feature(irrefutable_let_patterns)]
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#[allow(irrefutable_let_patterns)]
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fn main() {
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use std::ops::Range;
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if let Range { start: _, end: _ } = true..true && false { }
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//~^ WARN error in 2018
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if let Range { start: _, end: _ } = true..true || false { }
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//~^ WARN error in 2018
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while let Range { start: _, end: _ } = true..true && false { }
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//~^ WARN error in 2018
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while let Range { start: _, end: _ } = true..true || false { }
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//~^ WARN error in 2018
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if let true = false && false { }
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//~^ WARN error in 2018
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while let true = (1 == 2) && false { }
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//~^ WARN error in 2018
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// The following cases are not an error as parenthesis are used to
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// clarify intent:
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if let Range { start: _, end: _ } = true..(true || false) { }
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if let Range { start: _, end: _ } = true..(true && false) { }
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while let Range { start: _, end: _ } = true..(true || false) { }
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while let Range { start: _, end: _ } = true..(true && false) { }
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}

‎src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2015.stderr

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warning: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2015.rs:22:47
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|
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LL | if let Range { start: _, end: _ } = true..true && false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true && false)`
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|
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= note: This will be a error in Rust 2018 until the `let_chains` feature is stabilized.
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warning: ambigious use of `||`
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--> $DIR/syntax-ambiguity-2015.rs:25:47
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|
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LL | if let Range { start: _, end: _ } = true..true || false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true || false)`
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|
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= note: This will be a error in Rust 2018 until the `let_chains` feature is stabilized.
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warning: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2015.rs:28:50
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|
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LL | while let Range { start: _, end: _ } = true..true && false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true && false)`
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|
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= note: This will be a error in Rust 2018 until the `let_chains` feature is stabilized.
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warning: ambigious use of `||`
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--> $DIR/syntax-ambiguity-2015.rs:31:50
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|
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LL | while let Range { start: _, end: _ } = true..true || false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true || false)`
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|
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= note: This will be a error in Rust 2018 until the `let_chains` feature is stabilized.
32+
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warning: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2015.rs:34:19
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|
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LL | if let true = false && false { }
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| ^^^^^^^^^^^^^^ help: consider adding parenthesis: `(false && false)`
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|
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= note: This will be a error in Rust 2018 until the `let_chains` feature is stabilized.
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warning: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2015.rs:37:22
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|
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LL | while let true = (1 == 2) && false { }
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| ^^^^^^^^^^^^^^^^^ help: consider adding parenthesis: `((1 == 2) && false)`
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|
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= note: This will be a error in Rust 2018 until the `let_chains` feature is stabilized.
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‎src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.rs

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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
9+
// except according to those terms.
10+
11+
// edition:2018
12+
13+
// Enabling `ireffutable_let_patterns` isn't necessary for what this tests, but it makes coming up
14+
// with examples easier.
15+
#![feature(irrefutable_let_patterns)]
16+
17+
#[allow(irrefutable_let_patterns)]
18+
fn main() {
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use std::ops::Range;
20+
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if let Range { start: _, end: _ } = true..true && false { }
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//~^ ERROR ambigious use of `&&`
23+
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if let Range { start: _, end: _ } = true..true || false { }
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//~^ ERROR ambigious use of `||`
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while let Range { start: _, end: _ } = true..true && false { }
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//~^ ERROR ambigious use of `&&`
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while let Range { start: _, end: _ } = true..true || false { }
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//~^ ERROR ambigious use of `||`
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if let true = false && false { }
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//~^ ERROR ambigious use of `&&`
35+
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while let true = (1 == 2) && false { }
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//~^ ERROR ambigious use of `&&`
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// The following cases are not an error as parenthesis are used to
40+
// clarify intent:
41+
42+
if let Range { start: _, end: _ } = true..(true || false) { }
43+
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if let Range { start: _, end: _ } = true..(true && false) { }
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while let Range { start: _, end: _ } = true..(true || false) { }
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while let Range { start: _, end: _ } = true..(true && false) { }
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}

‎src/test/ui/rfc-2497-if-let-chains/syntax-ambiguity-2018.stderr

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error: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2018.rs:21:47
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|
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LL | if let Range { start: _, end: _ } = true..true && false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true && false)`
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|
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= note: This will be a error until the `let_chains` feature is stabilized.
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error: ambigious use of `||`
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--> $DIR/syntax-ambiguity-2018.rs:24:47
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|
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LL | if let Range { start: _, end: _ } = true..true || false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true || false)`
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|
15+
= note: This will be a error until the `let_chains` feature is stabilized.
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error: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2018.rs:27:50
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|
20+
LL | while let Range { start: _, end: _ } = true..true && false { }
21+
| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true && false)`
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|
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= note: This will be a error until the `let_chains` feature is stabilized.
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error: ambigious use of `||`
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--> $DIR/syntax-ambiguity-2018.rs:30:50
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|
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LL | while let Range { start: _, end: _ } = true..true || false { }
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| ^^^^^^^^^^^^^ help: consider adding parenthesis: `(true || false)`
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|
31+
= note: This will be a error until the `let_chains` feature is stabilized.
32+
33+
error: ambigious use of `&&`
34+
--> $DIR/syntax-ambiguity-2018.rs:33:19
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|
36+
LL | if let true = false && false { }
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| ^^^^^^^^^^^^^^ help: consider adding parenthesis: `(false && false)`
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|
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= note: This will be a error until the `let_chains` feature is stabilized.
40+
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error: ambigious use of `&&`
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--> $DIR/syntax-ambiguity-2018.rs:36:22
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|
44+
LL | while let true = (1 == 2) && false { }
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| ^^^^^^^^^^^^^^^^^ help: consider adding parenthesis: `((1 == 2) && false)`
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|
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= note: This will be a error until the `let_chains` feature is stabilized.
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error: aborting due to 6 previous errors
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