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Merge pull request #552 from mcarton/for_loop
Handle more iterator adapter cases in for loops
This commit is contained in:
Manish Goregaokar
commit
604be945d2
136
src/loops.rs
136
src/loops.rs
@ -8,7 +8,6 @@ use consts::{constant_simple, Constant};
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use rustc::front::map::Node::NodeBlock;
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use std::borrow::Cow;
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use std::collections::{HashSet, HashMap};
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use syntax::ast::Lit_::*;
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use utils::{snippet, span_lint, get_parent_expr, match_trait_method, match_type, in_external_macro, expr_block,
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span_help_and_lint, is_integer_literal, get_enclosing_block};
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@ -247,54 +246,102 @@ impl LateLintPass for LoopsPass {
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}
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fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
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// check for looping over a range and then indexing a sequence with it
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// -> the iteratee must be a range literal
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if let ExprRange(Some(ref l), _) = arg.node {
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// Range should start with `0`
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if let ExprLit(ref lit) = l.node {
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if let LitInt(0, _) = lit.node {
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check_for_loop_range(cx, pat, arg, body, expr);
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check_for_loop_reverse_range(cx, arg, expr);
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check_for_loop_explicit_iter(cx, arg, expr);
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check_for_loop_explicit_counter(cx, arg, body, expr);
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}
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// the var must be a single name
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if let PatIdent(_, ref ident, _) = pat.node {
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let mut visitor = VarVisitor {
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cx: cx,
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var: ident.node.name,
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indexed: HashSet::new(),
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nonindex: false,
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};
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walk_expr(&mut visitor, body);
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// linting condition: we only indexed one variable
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if visitor.indexed.len() == 1 {
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let indexed = visitor.indexed
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.into_iter()
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.next()
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.expect("Len was nonzero, but no contents found");
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if visitor.nonindex {
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span_lint(cx,
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NEEDLESS_RANGE_LOOP,
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expr.span,
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&format!("the loop variable `{}` is used to index `{}`. Consider using `for \
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({}, item) in {}.iter().enumerate()` or similar iterators",
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ident.node.name,
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indexed,
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ident.node.name,
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indexed));
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} else {
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span_lint(cx,
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NEEDLESS_RANGE_LOOP,
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expr.span,
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&format!("the loop variable `{}` is only used to index `{}`. Consider using \
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`for item in &{}` or similar iterators",
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ident.node.name,
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indexed,
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indexed));
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}
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/// Check for looping over a range and then indexing a sequence with it.
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/// The iteratee must be a range literal.
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fn check_for_loop_range(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &Expr) {
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if let ExprRange(Some(ref l), ref r) = arg.node {
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// the var must be a single name
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if let PatIdent(_, ref ident, _) = pat.node {
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let mut visitor = VarVisitor {
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cx: cx,
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var: ident.node.name,
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indexed: HashSet::new(),
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nonindex: false,
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};
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walk_expr(&mut visitor, body);
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// linting condition: we only indexed one variable
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if visitor.indexed.len() == 1 {
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let indexed = visitor.indexed
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.into_iter()
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.next()
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.expect("Len was nonzero, but no contents found");
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let starts_at_zero = is_integer_literal(l, 0);
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let skip: Cow<_> = if starts_at_zero {
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"".into()
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}
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else {
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format!(".skip({})", snippet(cx, l.span, "..")).into()
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};
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let take: Cow<_> = if let Some(ref r) = *r {
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if !is_len_call(&r, &indexed) {
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format!(".take({})", snippet(cx, r.span, "..")).into()
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}
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else {
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"".into()
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}
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} else {
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"".into()
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};
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if visitor.nonindex {
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span_lint(cx,
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NEEDLESS_RANGE_LOOP,
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expr.span,
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&format!("the loop variable `{}` is used to index `{}`. \
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Consider using `for ({}, item) in {}.iter().enumerate(){}{}` or similar iterators",
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ident.node.name,
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indexed,
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ident.node.name,
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indexed,
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take,
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skip));
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} else {
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let repl = if starts_at_zero && take.is_empty() {
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format!("&{}", indexed)
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}
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else {
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format!("{}.iter(){}{}", indexed, take, skip)
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};
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span_lint(cx,
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NEEDLESS_RANGE_LOOP,
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expr.span,
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&format!("the loop variable `{}` is only used to index `{}`. \
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Consider using `for item in {}` or similar iterators",
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ident.node.name,
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indexed,
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repl));
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}
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}
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}
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}
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}
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fn is_len_call(expr: &Expr, var: &Name) -> bool {
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if_let_chain! {[
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let ExprMethodCall(method, _, ref len_args) = expr.node,
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len_args.len() == 1,
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method.node.as_str() == "len",
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let ExprPath(_, ref path) = len_args[0].node,
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path.segments.len() == 1,
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&path.segments[0].identifier.name == var
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], {
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return true;
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}}
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false
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}
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fn check_for_loop_reverse_range(cx: &LateContext, arg: &Expr, expr: &Expr) {
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// if this for loop is iterating over a two-sided range...
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if let ExprRange(Some(ref start_expr), Some(ref stop_expr)) = arg.node {
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// ...and both sides are compile-time constant integers...
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@ -324,7 +371,9 @@ fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &E
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}
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}
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}
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}
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fn check_for_loop_explicit_iter(cx: &LateContext, arg: &Expr, expr: &Expr) {
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if let ExprMethodCall(ref method, _, ref args) = arg.node {
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// just the receiver, no arguments
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if args.len() == 1 {
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@ -356,6 +405,9 @@ fn check_for_loop(cx: &LateContext, pat: &Pat, arg: &Expr, body: &Expr, expr: &E
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}
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}
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}
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fn check_for_loop_explicit_counter(cx: &LateContext, arg: &Expr, body: &Expr, expr: &Expr) {
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// Look for variables that are incremented once per loop iteration.
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let mut visitor = IncrementVisitor {
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cx: cx,
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@ -445,6 +445,7 @@ pub fn walk_ptrs_ty_depth(ty: ty::Ty) -> (ty::Ty, usize) {
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inner(ty, 0)
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}
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/// Check whether the given expression is a constant literal of the given value.
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pub fn is_integer_literal(expr: &Expr, value: u64) -> bool {
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// FIXME: use constant folding
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if let ExprLit(ref spanned) = expr.node {
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@ -20,20 +20,43 @@ impl Unrelated {
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fn main() {
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let mut vec = vec![1, 2, 3, 4];
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let vec2 = vec![1, 2, 3, 4];
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for i in 0..vec.len() { //~ERROR the loop variable `i` is only used to index `vec`.
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for i in 0..vec.len() {
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//~^ ERROR `i` is only used to index `vec`. Consider using `for item in &vec`
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println!("{}", vec[i]);
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}
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for i in 0..vec.len() { //~ERROR the loop variable `i` is used to index `vec`.
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for i in 0..vec.len() {
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//~^ ERROR `i` is used to index `vec`. Consider using `for (i, item) in vec.iter().enumerate()`
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println!("{} {}", vec[i], i);
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}
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for i in 0..vec.len() { // not an error, indexing more than one variable
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println!("{} {}", vec[i], vec2[i]);
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}
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for i in 5..vec.len() { // not an error, not starting with 0
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for i in 0..vec.len() {
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//~^ ERROR `i` is only used to index `vec2`. Consider using `for item in vec2.iter().take(vec.len())`
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println!("{}", vec2[i]);
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}
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for i in 5..vec.len() {
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//~^ ERROR `i` is only used to index `vec`. Consider using `for item in vec.iter().skip(5)`
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println!("{}", vec[i]);
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}
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for i in 5..10 {
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//~^ ERROR `i` is only used to index `vec`. Consider using `for item in vec.iter().take(10).skip(5)`
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println!("{}", vec[i]);
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}
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for i in 5..vec.len() {
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//~^ ERROR `i` is used to index `vec`. Consider using `for (i, item) in vec.iter().enumerate().skip(5)`
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println!("{} {}", vec[i], i);
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}
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for i in 5..10 {
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//~^ ERROR `i` is used to index `vec`. Consider using `for (i, item) in vec.iter().enumerate().take(10).skip(5)`
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println!("{} {}", vec[i], i);
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}
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for i in 10..0 { //~ERROR this range is empty so this for loop will never run
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println!("{}", i);
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}
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