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Merge pull request #552 from mcarton/for_loop

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Handle more iterator adapter cases in for loops
This commit is contained in:
Manish Goregaokar 2016-01-15 05:22:20 +05:30
commit 604be945d2
3 changed files with 121 additions and 45 deletions
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136
src/loops.rs
View file

@ -8,7 +8,6 @@ use consts::{constant_simple, Constant};
use rustc::front::map::Node::NodeBlock;
use std::borrow::Cow;
use std::collections::{HashSet, HashMap};
use syntax::ast::Lit_::*;
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};
@ -247,54 +246,102 @@ impl LateLintPass for LoopsPass {
}
fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
// check for looping over a range and then indexing a sequence with it
// -> the iteratee must be a range literal
if let ExprRange(Some(ref l), _) = arg.node {
// Range should start with `0`
if let ExprLit(ref lit) = l.node {
if let LitInt(0, _) = lit.node {
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_explicit_counter(cx, arg, body, expr);
}
// the var must be a single name
if let PatIdent(_, ref ident, _) = pat.node {
let mut visitor = VarVisitor {
cx: cx,
var: ident.node.name,
indexed: HashSet::new(),
nonindex: false,
};
walk_expr(&mut visitor, body);
// linting condition: we only indexed one variable
if visitor.indexed.len() == 1 {
let indexed = visitor.indexed
.into_iter()
.next()
.expect("Len was nonzero, but no contents found");
if visitor.nonindex {
span_lint(cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is used to index `{}`. Consider using `for \
({}, item) in {}.iter().enumerate()` or similar iterators",
ident.node.name,
indexed,
ident.node.name,
indexed));
} else {
span_lint(cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is only used to index `{}`. Consider using \
`for item in &{}` or similar iterators",
ident.node.name,
indexed,
indexed));
}
/// Check for looping over a range and then indexing a sequence with it.
/// The iteratee must be a range literal.
fn check_for_loop_range(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
if let ExprRange(Some(ref l), ref r) = arg.node {
// the var must be a single name
if let PatIdent(_, ref ident, _) = pat.node {
let mut visitor = VarVisitor {
cx: cx,
var: ident.node.name,
indexed: HashSet::new(),
nonindex: false,
};
walk_expr(&mut visitor, body);
// linting condition: we only indexed one variable
if visitor.indexed.len() == 1 {
let indexed = visitor.indexed
.into_iter()
.next()
.expect("Len was nonzero, but no contents found");
let starts_at_zero = is_integer_literal(l, 0);
let skip: Cow<_> = if starts_at_zero {
"".into()
}
else {
format!(".skip({})", snippet(cx, l.span, "..")).into()
};
let take: Cow<_> = if let Some(ref r) = *r {
if !is_len_call(&r, &indexed) {
format!(".take({})", snippet(cx, r.span, "..")).into()
}
else {
"".into()
}
} else {
"".into()
};
if visitor.nonindex {
span_lint(cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is used to index `{}`. \
Consider using `for ({}, item) in {}.iter().enumerate(){}{}` or similar iterators",
ident.node.name,
indexed,
ident.node.name,
indexed,
take,
skip));
} else {
let repl = if starts_at_zero && take.is_empty() {
format!("&{}", indexed)
}
else {
format!("{}.iter(){}{}", indexed, take, skip)
};
span_lint(cx,
NEEDLESS_RANGE_LOOP,
expr.span,
&format!("the loop variable `{}` is only used to index `{}`. \
Consider using `for item in {}` or similar iterators",
ident.node.name,
indexed,
repl));
}
}
}
}
}
fn is_len_call(expr: &Expr, var: &Name) -> bool {
if_let_chain! {[
let ExprMethodCall(method, _, ref len_args) = expr.node,
len_args.len() == 1,
method.node.as_str() == "len",
let ExprPath(_, ref path) = len_args[0].node,
path.segments.len() == 1,
&path.segments[0].identifier.name == var
], {
return true;
}}
false
}
fn check_for_loop_reverse_range(cx: &LateContext, arg: &Expr, expr: &Expr) {
// if this for loop is iterating over a two-sided range...
if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
// ...and both sides are compile-time constant integers...
@ -324,7 +371,9 @@ fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &E
}
}
}
}
fn check_for_loop_explicit_iter(cx: &LateContext, arg: &Expr, expr: &Expr) {
if let ExprMethodCall(ref method, _, ref args) = arg.node {
// just the receiver, no arguments
if args.len() == 1 {
@ -356,6 +405,9 @@ fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &E
}
}
}
fn check_for_loop_explicit_counter(cx: &LateContext, arg: &Expr, body: &Expr, expr: &Expr) {
// Look for variables that are incremented once per loop iteration.
let mut visitor = IncrementVisitor {
cx: cx,

1
src/utils.rs
View file

@ -445,6 +445,7 @@ pub fn walk_ptrs_ty_depth(ty: ty::Ty) -> (ty::Ty, usize) {
inner(ty, 0)
}
/// Check whether the given expression is a constant literal of the given value.
pub fn is_integer_literal(expr: &Expr, value: u64) -> bool {
// FIXME: use constant folding
if let ExprLit(ref spanned) = expr.node {

29
tests/compile-fail/for_loop.rs
View file

@ -20,20 +20,43 @@ impl Unrelated {
fn main() {
let mut vec = vec![1, 2, 3, 4];
let vec2 = vec![1, 2, 3, 4];
for i in 0..vec.len() { //~ERROR the loop variable `i` is only used to index `vec`.
for i in 0..vec.len() {
//~^ ERROR `i` is only used to index `vec`. Consider using `for item in &vec`
println!("{}", vec[i]);
}
for i in 0..vec.len() { //~ERROR the loop variable `i` is used to index `vec`.
for i in 0..vec.len() {
//~^ ERROR `i` is used to index `vec`. Consider using `for (i, item) in vec.iter().enumerate()`
println!("{} {}", vec[i], i);
}
for i in 0..vec.len() { // not an error, indexing more than one variable
println!("{} {}", vec[i], vec2[i]);
}
for i in 5..vec.len() { // not an error, not starting with 0
for i in 0..vec.len() {
//~^ ERROR `i` is only used to index `vec2`. Consider using `for item in vec2.iter().take(vec.len())`
println!("{}", vec2[i]);
}
for i in 5..vec.len() {
//~^ ERROR `i` is only used to index `vec`. Consider using `for item in vec.iter().skip(5)`
println!("{}", vec[i]);
}
for i in 5..10 {
//~^ ERROR `i` is only used to index `vec`. Consider using `for item in vec.iter().take(10).skip(5)`
println!("{}", vec[i]);
}
for i in 5..vec.len() {
//~^ ERROR `i` is used to index `vec`. Consider using `for (i, item) in vec.iter().enumerate().skip(5)`
println!("{} {}", vec[i], i);
}
for i in 5..10 {
//~^ ERROR `i` is used to index `vec`. Consider using `for (i, item) in vec.iter().enumerate().take(10).skip(5)`
println!("{} {}", vec[i], i);
}
for i in 10..0 { //~ERROR this range is empty so this for loop will never run
println!("{}", i);
}