diff --git a/CHANGELOG.md b/CHANGELOG.md
index 687f74472020..41c334c68169 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2135,6 +2135,7 @@ Released 2018-09-13
[`invisible_characters`]: https://rust-lang.github.io/rust-clippy/master/index.html#invisible_characters
[`items_after_statements`]: https://rust-lang.github.io/rust-clippy/master/index.html#items_after_statements
[`iter_cloned_collect`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_cloned_collect
+[`iter_count`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_count
[`iter_next_loop`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_next_loop
[`iter_next_slice`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_next_slice
[`iter_nth`]: https://rust-lang.github.io/rust-clippy/master/index.html#iter_nth
diff --git a/clippy_lints/src/lib.rs b/clippy_lints/src/lib.rs
index fa8f03eb4453..1ace4c8a10c9 100644
--- a/clippy_lints/src/lib.rs
+++ b/clippy_lints/src/lib.rs
@@ -775,6 +775,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
&methods::INTO_ITER_ON_REF,
&methods::ITERATOR_STEP_BY_ZERO,
&methods::ITER_CLONED_COLLECT,
+ &methods::ITER_COUNT,
&methods::ITER_NEXT_SLICE,
&methods::ITER_NTH,
&methods::ITER_NTH_ZERO,
@@ -1577,6 +1578,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&methods::INTO_ITER_ON_REF),
LintId::of(&methods::ITERATOR_STEP_BY_ZERO),
LintId::of(&methods::ITER_CLONED_COLLECT),
+ LintId::of(&methods::ITER_COUNT),
LintId::of(&methods::ITER_NEXT_SLICE),
LintId::of(&methods::ITER_NTH),
LintId::of(&methods::ITER_NTH_ZERO),
@@ -1881,6 +1883,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
LintId::of(&methods::FILTER_NEXT),
LintId::of(&methods::FLAT_MAP_IDENTITY),
LintId::of(&methods::INSPECT_FOR_EACH),
+ LintId::of(&methods::ITER_COUNT),
LintId::of(&methods::MANUAL_FILTER_MAP),
LintId::of(&methods::MANUAL_FIND_MAP),
LintId::of(&methods::OPTION_AS_REF_DEREF),
diff --git a/clippy_lints/src/methods/iter_count.rs b/clippy_lints/src/methods/iter_count.rs
new file mode 100644
index 000000000000..1b99bacc3f1c
--- /dev/null
+++ b/clippy_lints/src/methods/iter_count.rs
@@ -0,0 +1,47 @@
+use crate::methods::derefs_to_slice;
+use crate::utils::{is_type_diagnostic_item, match_type, paths, snippet_with_applicability, span_lint_and_sugg};
+
+use rustc_errors::Applicability;
+use rustc_hir::Expr;
+use rustc_lint::LateContext;
+use rustc_span::sym;
+
+use super::ITER_COUNT;
+
+pub(crate) fn lints<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, iter_args: &'tcx [Expr<'tcx>], iter_method: &str) {
+ let ty = cx.typeck_results().expr_ty(&iter_args[0]);
+ let caller_type = if derefs_to_slice(cx, &iter_args[0], ty).is_some() {
+ "slice"
+ } else if is_type_diagnostic_item(cx, ty, sym::vec_type) {
+ "Vec"
+ } else if is_type_diagnostic_item(cx, ty, sym!(vecdeque_type)) {
+ "VecDeque"
+ } else if is_type_diagnostic_item(cx, ty, sym!(hashset_type)) {
+ "HashSet"
+ } else if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) {
+ "HashMap"
+ } else if match_type(cx, ty, &paths::BTREEMAP) {
+ "BTreeMap"
+ } else if match_type(cx, ty, &paths::BTREESET) {
+ "BTreeSet"
+ } else if match_type(cx, ty, &paths::LINKED_LIST) {
+ "LinkedList"
+ } else if match_type(cx, ty, &paths::BINARY_HEAP) {
+ "BinaryHeap"
+ } else {
+ return;
+ };
+ let mut applicability = Applicability::MachineApplicable;
+ span_lint_and_sugg(
+ cx,
+ ITER_COUNT,
+ expr.span,
+ &format!("called `.{}().count()` on a `{}`", iter_method, caller_type),
+ "try",
+ format!(
+ "{}.len()",
+ snippet_with_applicability(cx, iter_args[0].span, "..", &mut applicability),
+ ),
+ applicability,
+ );
+}
diff --git a/clippy_lints/src/methods/mod.rs b/clippy_lints/src/methods/mod.rs
index 6f491144435a..4a63de3cf48d 100644
--- a/clippy_lints/src/methods/mod.rs
+++ b/clippy_lints/src/methods/mod.rs
@@ -4,6 +4,7 @@ mod filter_map_identity;
mod implicit_clone;
mod inefficient_to_string;
mod inspect_for_each;
+mod iter_count;
mod manual_saturating_arithmetic;
mod option_map_unwrap_or;
mod unnecessary_filter_map;
@@ -1540,6 +1541,32 @@ declare_clippy_lint! {
"implicitly cloning a value by invoking a function on its dereferenced type"
}
+declare_clippy_lint! {
+ /// **What it does:** Checks for the use of `.iter().count()`.
+ ///
+ /// **Why is this bad?** `.len()` is more efficient and more
+ /// readable.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// ```rust
+ /// // Bad
+ /// let some_vec = vec![0, 1, 2, 3];
+ /// let _ = some_vec.iter().count();
+ /// let _ = &some_vec[..].iter().count();
+ ///
+ /// // Good
+ /// let some_vec = vec![0, 1, 2, 3];
+ /// let _ = some_vec.len();
+ /// let _ = &some_vec[..].len();
+ /// ```
+ pub ITER_COUNT,
+ complexity,
+ "replace `.iter().count()` with `.len()`"
+}
+
pub struct Methods {
msrv: Option<RustcVersion>,
}
@@ -1585,6 +1612,7 @@ impl_lint_pass!(Methods => [
MAP_FLATTEN,
ITERATOR_STEP_BY_ZERO,
ITER_NEXT_SLICE,
+ ITER_COUNT,
ITER_NTH,
ITER_NTH_ZERO,
BYTES_NTH,
@@ -1664,6 +1692,9 @@ impl<'tcx> LateLintPass<'tcx> for Methods {
lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
},
["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
+ ["count", "into_iter"] => iter_count::lints(cx, expr, &arg_lists[1], "into_iter"),
+ ["count", "iter"] => iter_count::lints(cx, expr, &arg_lists[1], "iter"),
+ ["count", "iter_mut"] => iter_count::lints(cx, expr, &arg_lists[1], "iter_mut"),
["nth", "iter"] => lint_iter_nth(cx, expr, &arg_lists, false),
["nth", "iter_mut"] => lint_iter_nth(cx, expr, &arg_lists, true),
["nth", "bytes"] => bytes_nth::lints(cx, expr, &arg_lists[1]),
diff --git a/tests/ui/auxiliary/option_helpers.rs b/tests/ui/auxiliary/option_helpers.rs
index ed11c41e21c1..7dc3f4ebd4d4 100644
--- a/tests/ui/auxiliary/option_helpers.rs
+++ b/tests/ui/auxiliary/option_helpers.rs
@@ -48,4 +48,8 @@ impl IteratorFalsePositives {
pub fn skip_while(self) -> IteratorFalsePositives {
self
}
+
+ pub fn count(self) -> usize {
+ self.foo as usize
+ }
}
diff --git a/tests/ui/iter_count.fixed b/tests/ui/iter_count.fixed
new file mode 100644
index 000000000000..b11dadda6c24
--- /dev/null
+++ b/tests/ui/iter_count.fixed
@@ -0,0 +1,86 @@
+// run-rustfix
+// aux-build:option_helpers.rs
+
+#![warn(clippy::iter_count)]
+#![allow(
+ unused_variables,
+ array_into_iter,
+ unused_mut,
+ clippy::into_iter_on_ref,
+ clippy::unnecessary_operation
+)]
+
+extern crate option_helpers;
+
+use option_helpers::IteratorFalsePositives;
+use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, LinkedList, VecDeque};
+
+/// Struct to generate false positives for things with `.iter()`.
+#[derive(Copy, Clone)]
+struct HasIter;
+
+impl HasIter {
+ fn iter(self) -> IteratorFalsePositives {
+ IteratorFalsePositives { foo: 0 }
+ }
+
+ fn iter_mut(self) -> IteratorFalsePositives {
+ IteratorFalsePositives { foo: 0 }
+ }
+
+ fn into_iter(self) -> IteratorFalsePositives {
+ IteratorFalsePositives { foo: 0 }
+ }
+}
+
+fn main() {
+ let mut vec = vec![0, 1, 2, 3];
+ let mut boxed_slice: Box<[u8]> = Box::new([0, 1, 2, 3]);
+ let mut vec_deque: VecDeque<_> = vec.iter().cloned().collect();
+ let mut hash_set = HashSet::new();
+ let mut hash_map = HashMap::new();
+ let mut b_tree_map = BTreeMap::new();
+ let mut b_tree_set = BTreeSet::new();
+ let mut linked_list = LinkedList::new();
+ let mut binary_heap = BinaryHeap::new();
+ hash_set.insert(1);
+ hash_map.insert(1, 2);
+ b_tree_map.insert(1, 2);
+ b_tree_set.insert(1);
+ linked_list.push_back(1);
+ binary_heap.push(1);
+
+ &vec[..].len();
+ vec.len();
+ boxed_slice.len();
+ vec_deque.len();
+ hash_set.len();
+ hash_map.len();
+ b_tree_map.len();
+ b_tree_set.len();
+ linked_list.len();
+ binary_heap.len();
+
+ vec.len();
+ &vec[..].len();
+ vec_deque.len();
+ hash_map.len();
+ b_tree_map.len();
+ linked_list.len();
+
+ &vec[..].len();
+ vec.len();
+ vec_deque.len();
+ hash_set.len();
+ hash_map.len();
+ b_tree_map.len();
+ b_tree_set.len();
+ linked_list.len();
+ binary_heap.len();
+
+ // Make sure we don't lint for non-relevant types.
+ let false_positive = HasIter;
+ false_positive.iter().count();
+ false_positive.iter_mut().count();
+ false_positive.into_iter().count();
+}
diff --git a/tests/ui/iter_count.rs b/tests/ui/iter_count.rs
new file mode 100644
index 000000000000..7d49c6a3dbbb
--- /dev/null
+++ b/tests/ui/iter_count.rs
@@ -0,0 +1,86 @@
+// run-rustfix
+// aux-build:option_helpers.rs
+
+#![warn(clippy::iter_count)]
+#![allow(
+ unused_variables,
+ array_into_iter,
+ unused_mut,
+ clippy::into_iter_on_ref,
+ clippy::unnecessary_operation
+)]
+
+extern crate option_helpers;
+
+use option_helpers::IteratorFalsePositives;
+use std::collections::{BTreeMap, BTreeSet, BinaryHeap, HashMap, HashSet, LinkedList, VecDeque};
+
+/// Struct to generate false positives for things with `.iter()`.
+#[derive(Copy, Clone)]
+struct HasIter;
+
+impl HasIter {
+ fn iter(self) -> IteratorFalsePositives {
+ IteratorFalsePositives { foo: 0 }
+ }
+
+ fn iter_mut(self) -> IteratorFalsePositives {
+ IteratorFalsePositives { foo: 0 }
+ }
+
+ fn into_iter(self) -> IteratorFalsePositives {
+ IteratorFalsePositives { foo: 0 }
+ }
+}
+
+fn main() {
+ let mut vec = vec![0, 1, 2, 3];
+ let mut boxed_slice: Box<[u8]> = Box::new([0, 1, 2, 3]);
+ let mut vec_deque: VecDeque<_> = vec.iter().cloned().collect();
+ let mut hash_set = HashSet::new();
+ let mut hash_map = HashMap::new();
+ let mut b_tree_map = BTreeMap::new();
+ let mut b_tree_set = BTreeSet::new();
+ let mut linked_list = LinkedList::new();
+ let mut binary_heap = BinaryHeap::new();
+ hash_set.insert(1);
+ hash_map.insert(1, 2);
+ b_tree_map.insert(1, 2);
+ b_tree_set.insert(1);
+ linked_list.push_back(1);
+ binary_heap.push(1);
+
+ &vec[..].iter().count();
+ vec.iter().count();
+ boxed_slice.iter().count();
+ vec_deque.iter().count();
+ hash_set.iter().count();
+ hash_map.iter().count();
+ b_tree_map.iter().count();
+ b_tree_set.iter().count();
+ linked_list.iter().count();
+ binary_heap.iter().count();
+
+ vec.iter_mut().count();
+ &vec[..].iter_mut().count();
+ vec_deque.iter_mut().count();
+ hash_map.iter_mut().count();
+ b_tree_map.iter_mut().count();
+ linked_list.iter_mut().count();
+
+ &vec[..].into_iter().count();
+ vec.into_iter().count();
+ vec_deque.into_iter().count();
+ hash_set.into_iter().count();
+ hash_map.into_iter().count();
+ b_tree_map.into_iter().count();
+ b_tree_set.into_iter().count();
+ linked_list.into_iter().count();
+ binary_heap.into_iter().count();
+
+ // Make sure we don't lint for non-relevant types.
+ let false_positive = HasIter;
+ false_positive.iter().count();
+ false_positive.iter_mut().count();
+ false_positive.into_iter().count();
+}
diff --git a/tests/ui/iter_count.stderr b/tests/ui/iter_count.stderr
new file mode 100644
index 000000000000..f3fb98e65b99
--- /dev/null
+++ b/tests/ui/iter_count.stderr
@@ -0,0 +1,154 @@
+error: called `.iter().count()` on a `slice`
+ --> $DIR/iter_count.rs:53:6
+ |
+LL | &vec[..].iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec[..].len()`
+ |
+ = note: `-D clippy::iter-count` implied by `-D warnings`
+
+error: called `.iter().count()` on a `Vec`
+ --> $DIR/iter_count.rs:54:5
+ |
+LL | vec.iter().count();
+ | ^^^^^^^^^^^^^^^^^^ help: try: `vec.len()`
+
+error: called `.iter().count()` on a `slice`
+ --> $DIR/iter_count.rs:55:5
+ |
+LL | boxed_slice.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `boxed_slice.len()`
+
+error: called `.iter().count()` on a `VecDeque`
+ --> $DIR/iter_count.rs:56:5
+ |
+LL | vec_deque.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec_deque.len()`
+
+error: called `.iter().count()` on a `HashSet`
+ --> $DIR/iter_count.rs:57:5
+ |
+LL | hash_set.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `hash_set.len()`
+
+error: called `.iter().count()` on a `HashMap`
+ --> $DIR/iter_count.rs:58:5
+ |
+LL | hash_map.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `hash_map.len()`
+
+error: called `.iter().count()` on a `BTreeMap`
+ --> $DIR/iter_count.rs:59:5
+ |
+LL | b_tree_map.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b_tree_map.len()`
+
+error: called `.iter().count()` on a `BTreeSet`
+ --> $DIR/iter_count.rs:60:5
+ |
+LL | b_tree_set.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b_tree_set.len()`
+
+error: called `.iter().count()` on a `LinkedList`
+ --> $DIR/iter_count.rs:61:5
+ |
+LL | linked_list.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `linked_list.len()`
+
+error: called `.iter().count()` on a `BinaryHeap`
+ --> $DIR/iter_count.rs:62:5
+ |
+LL | binary_heap.iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `binary_heap.len()`
+
+error: called `.iter_mut().count()` on a `Vec`
+ --> $DIR/iter_count.rs:64:5
+ |
+LL | vec.iter_mut().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.len()`
+
+error: called `.iter_mut().count()` on a `slice`
+ --> $DIR/iter_count.rs:65:6
+ |
+LL | &vec[..].iter_mut().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec[..].len()`
+
+error: called `.iter_mut().count()` on a `VecDeque`
+ --> $DIR/iter_count.rs:66:5
+ |
+LL | vec_deque.iter_mut().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec_deque.len()`
+
+error: called `.iter_mut().count()` on a `HashMap`
+ --> $DIR/iter_count.rs:67:5
+ |
+LL | hash_map.iter_mut().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `hash_map.len()`
+
+error: called `.iter_mut().count()` on a `BTreeMap`
+ --> $DIR/iter_count.rs:68:5
+ |
+LL | b_tree_map.iter_mut().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b_tree_map.len()`
+
+error: called `.iter_mut().count()` on a `LinkedList`
+ --> $DIR/iter_count.rs:69:5
+ |
+LL | linked_list.iter_mut().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `linked_list.len()`
+
+error: called `.into_iter().count()` on a `slice`
+ --> $DIR/iter_count.rs:71:6
+ |
+LL | &vec[..].into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec[..].len()`
+
+error: called `.into_iter().count()` on a `Vec`
+ --> $DIR/iter_count.rs:72:5
+ |
+LL | vec.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec.len()`
+
+error: called `.into_iter().count()` on a `VecDeque`
+ --> $DIR/iter_count.rs:73:5
+ |
+LL | vec_deque.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `vec_deque.len()`
+
+error: called `.into_iter().count()` on a `HashSet`
+ --> $DIR/iter_count.rs:74:5
+ |
+LL | hash_set.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `hash_set.len()`
+
+error: called `.into_iter().count()` on a `HashMap`
+ --> $DIR/iter_count.rs:75:5
+ |
+LL | hash_map.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `hash_map.len()`
+
+error: called `.into_iter().count()` on a `BTreeMap`
+ --> $DIR/iter_count.rs:76:5
+ |
+LL | b_tree_map.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b_tree_map.len()`
+
+error: called `.into_iter().count()` on a `BTreeSet`
+ --> $DIR/iter_count.rs:77:5
+ |
+LL | b_tree_set.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `b_tree_set.len()`
+
+error: called `.into_iter().count()` on a `LinkedList`
+ --> $DIR/iter_count.rs:78:5
+ |
+LL | linked_list.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `linked_list.len()`
+
+error: called `.into_iter().count()` on a `BinaryHeap`
+ --> $DIR/iter_count.rs:79:5
+ |
+LL | binary_heap.into_iter().count();
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `binary_heap.len()`
+
+error: aborting due to 25 previous errors
+
diff --git a/tests/ui/needless_collect.fixed b/tests/ui/needless_collect.fixed
index 7f2fcf02f6b5..af6c7bf15ea6 100644
--- a/tests/ui/needless_collect.fixed
+++ b/tests/ui/needless_collect.fixed
@@ -1,6 +1,6 @@
// run-rustfix
-#![allow(unused, clippy::suspicious_map)]
+#![allow(unused, clippy::suspicious_map, clippy::iter_count)]
use std::collections::{BTreeSet, HashMap, HashSet};
diff --git a/tests/ui/needless_collect.rs b/tests/ui/needless_collect.rs
index 788a9eb3264e..6ae14f370b14 100644
--- a/tests/ui/needless_collect.rs
+++ b/tests/ui/needless_collect.rs
@@ -1,6 +1,6 @@
// run-rustfix
-#![allow(unused, clippy::suspicious_map)]
+#![allow(unused, clippy::suspicious_map, clippy::iter_count)]
use std::collections::{BTreeSet, HashMap, HashSet};