From 60d38ee1dde4344daa5fdf716eef78b45f483c7e Mon Sep 17 00:00:00 2001 From: Eduardo Broto Date: Sat, 23 May 2020 22:07:03 +0200 Subject: [PATCH] reversed_empty_ranges: add suggestion for &slice[N..N] --- clippy_lints/src/ranges.rs | 30 ++++++++++++++----- tests/ui/reversed_empty_ranges_fixable.fixed | 7 ++++- tests/ui/reversed_empty_ranges_fixable.rs | 7 ++++- tests/ui/reversed_empty_ranges_fixable.stderr | 16 ++++++---- tests/ui/reversed_empty_ranges_unfixable.rs | 1 - .../ui/reversed_empty_ranges_unfixable.stderr | 10 ++----- 6 files changed, 47 insertions(+), 24 deletions(-) diff --git a/clippy_lints/src/ranges.rs b/clippy_lints/src/ranges.rs index 83c6faac041..1eb26d97ed4 100644 --- a/clippy_lints/src/ranges.rs +++ b/clippy_lints/src/ranges.rs @@ -241,14 +241,14 @@ fn check_inclusive_range_minus_one(cx: &LateContext<'_, '_>, expr: &Expr<'_>) { } fn check_reversed_empty_range(cx: &LateContext<'_, '_>, expr: &Expr<'_>) { - fn inside_indexing_expr(cx: &LateContext<'_, '_>, expr: &Expr<'_>) -> bool { - matches!( - get_parent_expr(cx, expr), - Some(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 { @@ -267,18 +267,32 @@ fn check_reversed_empty_range(cx: &LateContext<'_, '_>, expr: &Expr<'_>) { if let Some(ordering) = Constant::partial_cmp(cx.tcx, ty, &start_idx, &end_idx); if is_empty_range(limits, ordering); then { - if inside_indexing_expr(cx, expr) { + 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( + 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( diff --git a/tests/ui/reversed_empty_ranges_fixable.fixed b/tests/ui/reversed_empty_ranges_fixable.fixed index ee2cbc3cf54..332c0427ef6 100644 --- a/tests/ui/reversed_empty_ranges_fixable.fixed +++ b/tests/ui/reversed_empty_ranges_fixable.fixed @@ -4,18 +4,23 @@ const ANSWER: i32 = 42; fn main() { + let arr = [1, 2, 3, 4, 5]; + + // These should be linted: + (21..=42).rev().for_each(|x| println!("{}", x)); let _ = (21..ANSWER).rev().filter(|x| x % 2 == 0).take(10).collect::>(); for _ in (-42..=-21).rev() {} for _ in (21u32..42u32).rev() {} + let _ = &[] as &[i32]; + // These should be ignored as they are not empty ranges: (21..=42).for_each(|x| println!("{}", x)); (21..42).for_each(|x| println!("{}", x)); - let arr = [1, 2, 3, 4, 5]; let _ = &arr[1..=3]; let _ = &arr[1..3]; diff --git a/tests/ui/reversed_empty_ranges_fixable.rs b/tests/ui/reversed_empty_ranges_fixable.rs index 6ed5ca6daa0..901ec8bcc09 100644 --- a/tests/ui/reversed_empty_ranges_fixable.rs +++ b/tests/ui/reversed_empty_ranges_fixable.rs @@ -4,18 +4,23 @@ const ANSWER: i32 = 42; fn main() { + let arr = [1, 2, 3, 4, 5]; + + // These should be linted: + (42..=21).for_each(|x| println!("{}", x)); let _ = (ANSWER..21).filter(|x| x % 2 == 0).take(10).collect::>(); for _ in -21..=-42 {} for _ in 42u32..21u32 {} + let _ = &arr[3..3]; + // These should be ignored as they are not empty ranges: (21..=42).for_each(|x| println!("{}", x)); (21..42).for_each(|x| println!("{}", x)); - let arr = [1, 2, 3, 4, 5]; let _ = &arr[1..=3]; let _ = &arr[1..3]; diff --git a/tests/ui/reversed_empty_ranges_fixable.stderr b/tests/ui/reversed_empty_ranges_fixable.stderr index 97933b8ff85..9a646fd9939 100644 --- a/tests/ui/reversed_empty_ranges_fixable.stderr +++ b/tests/ui/reversed_empty_ranges_fixable.stderr @@ -1,5 +1,5 @@ error: this range is empty so it will yield no values - --> $DIR/reversed_empty_ranges_fixable.rs:7:5 + --> $DIR/reversed_empty_ranges_fixable.rs:11:5 | LL | (42..=21).for_each(|x| println!("{}", x)); | ^^^^^^^^^ @@ -11,7 +11,7 @@ LL | (21..=42).rev().for_each(|x| println!("{}", x)); | ^^^^^^^^^^^^^^^ error: this range is empty so it will yield no values - --> $DIR/reversed_empty_ranges_fixable.rs:8:13 + --> $DIR/reversed_empty_ranges_fixable.rs:12:13 | LL | let _ = (ANSWER..21).filter(|x| x % 2 == 0).take(10).collect::>(); | ^^^^^^^^^^^^ @@ -22,7 +22,7 @@ LL | let _ = (21..ANSWER).rev().filter(|x| x % 2 == 0).take(10).collect:: $DIR/reversed_empty_ranges_fixable.rs:10:14 + --> $DIR/reversed_empty_ranges_fixable.rs:14:14 | LL | for _ in -21..=-42 {} | ^^^^^^^^^ @@ -33,7 +33,7 @@ LL | for _ in (-42..=-21).rev() {} | ^^^^^^^^^^^^^^^^^ error: this range is empty so it will yield no values - --> $DIR/reversed_empty_ranges_fixable.rs:11:14 + --> $DIR/reversed_empty_ranges_fixable.rs:15:14 | LL | for _ in 42u32..21u32 {} | ^^^^^^^^^^^^ @@ -43,5 +43,11 @@ help: consider using the following if you are attempting to iterate over this ra LL | for _ in (21u32..42u32).rev() {} | ^^^^^^^^^^^^^^^^^^^^ -error: aborting due to 4 previous errors +error: this range is empty and using it to index a slice will always yield an empty slice + --> $DIR/reversed_empty_ranges_fixable.rs:17:18 + | +LL | let _ = &arr[3..3]; + | ----^^^^- help: if you want an empty slice, use: `[] as &[i32]` + +error: aborting due to 5 previous errors diff --git a/tests/ui/reversed_empty_ranges_unfixable.rs b/tests/ui/reversed_empty_ranges_unfixable.rs index c9ca4c47668..561a35625f0 100644 --- a/tests/ui/reversed_empty_ranges_unfixable.rs +++ b/tests/ui/reversed_empty_ranges_unfixable.rs @@ -9,7 +9,6 @@ fn main() { let arr = [1, 2, 3, 4, 5]; let _ = &arr[3usize..=1usize]; let _ = &arr[SOME_NUM..1]; - let _ = &arr[3..3]; for _ in ANSWER..ANSWER {} } diff --git a/tests/ui/reversed_empty_ranges_unfixable.stderr b/tests/ui/reversed_empty_ranges_unfixable.stderr index 12e5483ecdf..240188cbb46 100644 --- a/tests/ui/reversed_empty_ranges_unfixable.stderr +++ b/tests/ui/reversed_empty_ranges_unfixable.stderr @@ -18,17 +18,11 @@ error: this range is reversed and using it to index a slice will panic at run-ti LL | let _ = &arr[SOME_NUM..1]; | ^^^^^^^^^^^ -error: this range is empty and using it to index a slice will always yield an empty slice - --> $DIR/reversed_empty_ranges_unfixable.rs:12:18 - | -LL | let _ = &arr[3..3]; - | ^^^^ - error: this range is empty so it will yield no values - --> $DIR/reversed_empty_ranges_unfixable.rs:14:14 + --> $DIR/reversed_empty_ranges_unfixable.rs:13:14 | LL | for _ in ANSWER..ANSWER {} | ^^^^^^^^^^^^^^ -error: aborting due to 5 previous errors +error: aborting due to 4 previous errors