+use crate::consts::{constant, Constant};
use if_chain::if_chain;
use rustc_ast::ast::RangeLimits;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind, QPath};
use rustc_lint::{LateContext, LateLintPass};
+use rustc_middle::ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
+use std::cmp::Ordering;
use crate::utils::sugg::Sugg;
+use crate::utils::{get_parent_expr, is_integer_const, snippet, snippet_opt, span_lint, span_lint_and_then};
use crate::utils::{higher, SpanlessEq};
-use crate::utils::{is_integer_const, snippet, snippet_opt, span_lint, span_lint_and_then};
declare_clippy_lint! {
/// **What it does:** Checks for zipping a collection with the range of
"`x..=(y-1)` reads better as `x..y`"
}
+declare_clippy_lint! {
+ /// **What it does:** Checks for range expressions `x..y` where both `x` and `y`
+ /// are constant and `x` is greater or equal to `y`.
+ ///
+ /// **Why is this bad?** Empty ranges yield no values so iterating them is a no-op.
+ /// Moreover, trying to use a reversed range to index a slice will panic at run-time.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// ```rust,no_run
+ /// fn main() {
+ /// (10..=0).for_each(|x| println!("{}", x));
+ ///
+ /// let arr = [1, 2, 3, 4, 5];
+ /// let sub = &arr[3..1];
+ /// }
+ /// ```
+ /// Use instead:
+ /// ```rust
+ /// fn main() {
+ /// (0..=10).rev().for_each(|x| println!("{}", x));
+ ///
+ /// let arr = [1, 2, 3, 4, 5];
+ /// let sub = &arr[1..3];
+ /// }
+ /// ```
+ pub REVERSED_EMPTY_RANGES,
+ correctness,
+ "reversing the limits of range expressions, resulting in empty ranges"
+}
+
declare_lint_pass!(Ranges => [
RANGE_ZIP_WITH_LEN,
RANGE_PLUS_ONE,
- RANGE_MINUS_ONE
+ RANGE_MINUS_ONE,
+ REVERSED_EMPTY_RANGES,
]);
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Ranges {
check_exclusive_range_plus_one(cx, expr);
check_inclusive_range_minus_one(cx, expr);
+ check_reversed_empty_range(cx, expr);
}
}
RANGE_PLUS_ONE,
span,
"an inclusive range would be more readable",
- |db| {
+ |diag| {
let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
let end = Sugg::hir(cx, y, "y");
if let Some(is_wrapped) = &snippet_opt(cx, span) {
if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
- db.span_suggestion(
+ diag.span_suggestion(
span,
"use",
format!("({}..={})", start, end),
Applicability::MaybeIncorrect,
);
} else {
- db.span_suggestion(
+ diag.span_suggestion(
span,
"use",
format!("{}..={}", start, end),
RANGE_MINUS_ONE,
expr.span,
"an exclusive range would be more readable",
- |db| {
+ |diag| {
let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string());
let end = Sugg::hir(cx, y, "y");
- db.span_suggestion(
+ diag.span_suggestion(
expr.span,
"use",
format!("{}..{}", start, end),
}
}
+fn check_reversed_empty_range(cx: &LateContext<'_, '_>, expr: &Expr<'_>) {
+ fn inside_indexing_expr<'a>(cx: &'a LateContext<'_, '_>, expr: &Expr<'_>) -> Option<&'a Expr<'a>> {
+ match get_parent_expr(cx, expr) {
+ parent_expr @ Some(Expr {
+ kind: ExprKind::Index(..),
+ ..
+ }) => parent_expr,
+ _ => None,
+ }
+ }
+
+ fn is_empty_range(limits: RangeLimits, ordering: Ordering) -> bool {
+ match limits {
+ RangeLimits::HalfOpen => ordering != Ordering::Less,
+ RangeLimits::Closed => ordering == Ordering::Greater,
+ }
+ }
+
+ if_chain! {
+ if let Some(higher::Range { start: Some(start), end: Some(end), limits }) = higher::range(cx, expr);
+ let ty = cx.tables.expr_ty(start);
+ if let ty::Int(_) | ty::Uint(_) = ty.kind;
+ if let Some((start_idx, _)) = constant(cx, cx.tables, start);
+ if let Some((end_idx, _)) = constant(cx, cx.tables, end);
+ if let Some(ordering) = Constant::partial_cmp(cx.tcx, ty, &start_idx, &end_idx);
+ if is_empty_range(limits, ordering);
+ then {
+ if let Some(parent_expr) = inside_indexing_expr(cx, expr) {
+ let (reason, outcome) = if ordering == Ordering::Equal {
+ ("empty", "always yield an empty slice")
+ } else {
+ ("reversed", "panic at run-time")
+ };
+
+ span_lint_and_then(
+ cx,
+ REVERSED_EMPTY_RANGES,
+ expr.span,
+ &format!("this range is {} and using it to index a slice will {}", reason, outcome),
+ |diag| {
+ if_chain! {
+ if ordering == Ordering::Equal;
+ if let ty::Slice(slice_ty) = cx.tables.expr_ty(parent_expr).kind;
+ then {
+ diag.span_suggestion(
+ parent_expr.span,
+ "if you want an empty slice, use",
+ format!("[] as &[{}]", slice_ty),
+ Applicability::MaybeIncorrect
+ );
+ }
+ }
+ }
+ );
+ } else {
+ span_lint_and_then(
+ cx,
+ REVERSED_EMPTY_RANGES,
+ expr.span,
+ "this range is empty so it will yield no values",
+ |diag| {
+ if ordering != Ordering::Equal {
+ let start_snippet = snippet(cx, start.span, "_");
+ let end_snippet = snippet(cx, end.span, "_");
+ let dots = match limits {
+ RangeLimits::HalfOpen => "..",
+ RangeLimits::Closed => "..="
+ };
+
+ diag.span_suggestion(
+ expr.span,
+ "consider using the following if you are attempting to iterate over this \
+ range in reverse",
+ format!("({}{}{}).rev()", end_snippet, dots, start_snippet),
+ Applicability::MaybeIncorrect,
+ );
+ }
+ },
+ );
+ }
+ }
+ }
+}
+
fn y_plus_one<'t>(cx: &LateContext<'_, '_>, expr: &'t Expr<'_>) -> Option<&'t Expr<'t>> {
match expr.kind {
ExprKind::Binary(
projects / rust.git / blobdiff