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Add for_loop_over_option lint

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This commit is contained in:
Devon Hollowood
2016-01-28 23:34:09 -08:00
parent 783b342bc1
commit f5cc94c96a
4 changed files with 71 additions and 4 deletions
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3
README.md
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@@ -6,7 +6,7 @@ A collection of lints to catch common mistakes and improve your Rust code.
[Jump to usage instructions](#usage)
##Lints
There are 101 lints included in this crate:
There are 102 lints included in this crate:
name | default | meaning
---------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
@@ -37,6 +37,7 @@ name
[extend_from_slice](https://github.com/Manishearth/rust-clippy/wiki#extend_from_slice) | warn | `.extend_from_slice(_)` is a faster way to extend a Vec by a slice
[filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next) | warn | using `filter(p).next()`, which is more succinctly expressed as `.find(p)`
[float_cmp](https://github.com/Manishearth/rust-clippy/wiki#float_cmp) | warn | using `==` or `!=` on float values (as floating-point operations usually involve rounding errors, it is always better to check for approximate equality within small bounds)
[for_loop_over_option](https://github.com/Manishearth/rust-clippy/wiki#for_loop_over_option) | warn | for-looping over an Option, which is more clear as an `if let`
[identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op) | warn | using identity operations, e.g. `x + 0` or `y / 1`
[ineffective_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#ineffective_bit_mask) | warn | expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`
[inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always) | warn | `#[inline(always)]` is a bad idea in most cases

1
src/lib.rs
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@@ -192,6 +192,7 @@ pub fn plugin_registrar(reg: &mut Registry) {
loops::EMPTY_LOOP,
loops::EXPLICIT_COUNTER_LOOP,
loops::EXPLICIT_ITER_LOOP,
loops::FOR_LOOP_OVER_OPTION,
loops::ITER_NEXT_LOOP,
loops::NEEDLESS_RANGE_LOOP,
loops::REVERSE_RANGE_LOOP,

36
src/loops.rs
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@@ -11,7 +11,7 @@ use std::collections::{HashSet, HashMap};
use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type, in_external_macro, expr_block,
span_help_and_lint, is_integer_literal, get_enclosing_block};
use utils::{HASHMAP_PATH, VEC_PATH, LL_PATH};
use utils::{HASHMAP_PATH, VEC_PATH, LL_PATH, OPTION_PATH};
/// **What it does:** This lint checks for looping over the range of `0..len` of some collection just to get the values by index. It is `Warn` by default.
///
@@ -48,6 +48,16 @@ declare_lint!{ pub EXPLICIT_ITER_LOOP, Warn,
declare_lint!{ pub ITER_NEXT_LOOP, Warn,
"for-looping over `_.next()` which is probably not intended" }
/// **What it does:** This lint checks for `for` loops over Option values. It is `Warn` by default.
///
/// **Why is this bad?** Readability. This is more clearly expressed as an `if let`.
///
/// **Known problems:** None
///
/// **Example:** `for x in option { .. }`. This should be `if let Some(x) = option { .. }`.
declare_lint!{ pub FOR_LOOP_OVER_OPTION, Warn,
"for-looping over an Option, which is more clear as an `if let`" }
/// **What it does:** This lint detects `loop + match` combinations that are easier written as a `while let` loop. It is `Warn` by default.
///
/// **Why is this bad?** The `while let` loop is usually shorter and more readable
@@ -248,7 +258,7 @@ impl LateLintPass for LoopsPass {
fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
check_for_loop_range(cx, pat, arg, body, expr);
check_for_loop_reverse_range(cx, arg, expr);
check_for_loop_explicit_iter(cx, arg, expr);
check_for_loop_arg(cx, pat, arg, expr);
check_for_loop_explicit_counter(cx, arg, body, expr);
}
@@ -373,7 +383,8 @@ fn check_for_loop_reverse_range(cx: &LateContext, arg: &Expr, expr: &Expr) {
}
}
fn check_for_loop_explicit_iter(cx: &LateContext, arg: &Expr, expr: &Expr) {
fn check_for_loop_arg(cx: &LateContext, pat: &Pat, arg: &Expr, expr: &Expr) {
let mut next_loop_linted = false; // whether or not ITER_NEXT_LOOP lint was used
if let ExprMethodCall(ref method, _, ref args) = arg.node {
// just the receiver, no arguments
if args.len() == 1 {
@@ -401,10 +412,29 @@ fn check_for_loop_explicit_iter(cx: &LateContext, arg: &Expr, expr: &Expr) {
expr.span,
"you are iterating over `Iterator::next()` which is an Option; this will compile but is \
probably not what you want");
next_loop_linted = true;
}
}
}
if !next_loop_linted {
check_option_looping(cx, pat, arg);
}
}
/// Check for `for` loops over `Option`s
fn check_option_looping(cx: &LateContext, pat: &Pat, arg: &Expr) {
let ty = cx.tcx.expr_ty(arg);
if match_type(cx, ty, &OPTION_PATH) {
span_help_and_lint(
cx,
FOR_LOOP_OVER_OPTION,
arg.span,
&format!("for loop over `{0}`, which is an Option. This is more readably written as \
an `if let` statement.", snippet(cx, arg.span, "_")),
&format!("consider replacing `for {0} in {1}` with `if let Some({0}) = {1}`",
snippet(cx, pat.span, "_"), snippet(cx, arg.span, "_"))
);
}
}
fn check_for_loop_explicit_counter(cx: &LateContext, arg: &Expr, body: &Expr, expr: &Expr) {

35
tests/compile-fail/for_loop.rs
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@@ -3,6 +3,39 @@
use std::collections::*;
#[deny(clippy)]
fn for_loop_over_option() {
let option = Some(1);
let v = vec![0,1,2];
// check FOR_LOOP_OVER_OPTION lint
for x in option {
//~^ ERROR for loop over `option`, which is an Option.
//~| HELP consider replacing `for x in option` with `if let Some(x) = option`
println!("{}", x);
}
// make sure LOOP_OVER_NEXT lint takes precedence
for x in v.iter().next() {
//~^ ERROR you are iterating over `Iterator::next()` which is an Option
// TODO: make sure we don't lint twice
println!("{}", x);
}
// check for false positives
// for loop false positive
for x in v {
println!("{}", x);
}
// while let false positive
while let Some(x) = option {
println!("{}", x);
break;
}
}
struct Unrelated(Vec<u8>);
impl Unrelated {
fn next(&self) -> std::slice::Iter<u8> {
@@ -209,4 +242,6 @@ fn main() {
let mut index = 0;
for _v in &vec { index += 1 }
println!("index: {}", index);
for_loop_over_option();
}