rust-clippy/src/ranges.rs

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use rustc::lint::{Context, LintArray, LintPass};
use syntax::ast::*;
use syntax::codemap::Spanned;
use utils::match_type;
declare_lint! {
pub RANGE_STEP_BY_ZERO, Warn,
"using Range::step_by(0), which produces an infinite iterator"
}
#[derive(Copy,Clone)]
pub struct StepByZero;
impl LintPass for StepByZero {
fn get_lints(&self) -> LintArray {
lint_array!(RANGE_STEP_BY_ZERO)
}
fn check_expr(&mut self, cx: &Context, expr: &Expr) {
if let ExprMethodCall(Spanned { node: ref ident, .. }, _,
ref args) = expr.node {
// Only warn on literal ranges.
if ident.name.as_str() == "step_by" && args.len() == 2 &&
is_range(cx, &args[0]) && is_lit_zero(&args[1]) {
cx.span_lint(RANGE_STEP_BY_ZERO, expr.span,
"Range::step_by(0) produces an infinite iterator. \
Consider using `std::iter::repeat()` instead")
}
}
}
}
fn is_range(cx: &Context, expr: &Expr) -> bool {
// No need for walk_ptrs_ty here because step_by moves self, so it
// can't be called on a borrowed range.
let ty = cx.tcx.expr_ty(expr);
// Note: RangeTo and RangeFull don't have step_by
match_type(cx, ty, &["core", "ops", "Range"]) || match_type(cx, ty, &["core", "ops", "RangeFrom"])
}
fn is_lit_zero(expr: &Expr) -> bool {
// FIXME: use constant folding
if let ExprLit(ref spanned) = expr.node {
if let LitInt(0, _) = spanned.node {
return true;
}
}
false
}