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Merge pull request #3316 from pengowen123/fix_needless_range_loop

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Swap order of methods in `needless_range_loop` suggestion for efficiency in some cases
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Oliver S̶c̶h̶n̶e̶i̶d̶e̶r Scherer 2018-10-15 09:33:21 +02:00 • committed by GitHub
commit 0f4b13bc1b
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5 changed files with 69 additions and 7 deletions
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40
clippy_lints/src/loops.rs
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@ -27,6 +27,7 @@ use crate::rustc::ty::subst::Subst;
use crate::rustc_errors::Applicability;
use crate::rustc_data_structures::fx::{FxHashMap, FxHashSet};
use std::iter::{once, Iterator};
use std::mem;
use crate::syntax::ast;
use crate::syntax::source_map::Span;
use crate::syntax_pos::BytePos;
@ -1082,16 +1083,35 @@ fn check_for_loop_range<'a, 'tcx>(
format!(".skip({})", snippet(cx, start.span, ".."))
};
let mut end_is_start_plus_val = false;
let take = if let Some(end) = *end {
let mut take_expr = end;
if let ExprKind::Binary(ref op, ref left, ref right) = end.node {
if let BinOpKind::Add = op.node {
let start_equal_left = SpanlessEq::new(cx).eq_expr(start, left);
let start_equal_right = SpanlessEq::new(cx).eq_expr(start, right);
if start_equal_left {
take_expr = right;
} else if start_equal_right {
take_expr = left;
}
end_is_start_plus_val = start_equal_left | start_equal_right;
}
}
if is_len_call(end, indexed) {
String::new()
} else {
match limits {
ast::RangeLimits::Closed => {
let end = sugg::Sugg::hir(cx, end, "<count>");
format!(".take({})", end + sugg::ONE)
let take_expr = sugg::Sugg::hir(cx, take_expr, "<count>");
format!(".take({})", take_expr + sugg::ONE)
},
ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, end.span, "..")),
ast::RangeLimits::HalfOpen => format!(".take({})", snippet(cx, take_expr.span, "..")),
}
}
} else {
@ -1104,6 +1124,14 @@ fn check_for_loop_range<'a, 'tcx>(
("", "iter")
};
let take_is_empty = take.is_empty();
let mut method_1 = take;
let mut method_2 = skip;
if end_is_start_plus_val {
mem::swap(&mut method_1, &mut method_2);
}
if visitor.nonindex {
span_lint_and_then(
cx,
@ -1116,16 +1144,16 @@ fn check_for_loop_range<'a, 'tcx>(
"consider using an iterator".to_string(),
vec![
(pat.span, format!("({}, <item>)", ident.name)),
(arg.span, format!("{}.{}().enumerate(){}{}", indexed, method, take, skip)),
(arg.span, format!("{}.{}().enumerate(){}{}", indexed, method, method_1, method_2)),
],
);
},
);
} else {
let repl = if starts_at_zero && take.is_empty() {
let repl = if starts_at_zero && take_is_empty {
format!("&{}{}", ref_mut, indexed)
} else {
format!("{}.{}(){}{}", indexed, method, take, skip)
format!("{}.{}(){}{}", indexed, method, method_1, method_2)
};
span_lint_and_then(