Merge pull request #2350 from theotherphil/fold_any

Lint for using hand-writing a fold with the same behaviour as any

tests/ui/methods.rs

@@ -385,6 +385,42 @@ fn iter_skip_next() {
     let _ = foo.filter().skip(42).next();
 }
 
+/// Calls which should trigger the `UNNECESSARY_FOLD` lint
+fn unnecessary_fold() {
+    // Can be replaced by .any
+    let _ = (0..3).fold(false, |acc, x| acc || x > 2);
+    // Can be replaced by .all
+    let _ = (0..3).fold(true, |acc, x| acc && x > 2);
+    // Can be replaced by .sum
+    let _ = (0..3).fold(0, |acc, x| acc + x);
+    // Can be replaced by .product
+    let _ = (0..3).fold(1, |acc, x| acc * x);
+}
+
+/// Should trigger the `UNNECESSARY_FOLD` lint, with an error span including exactly `.fold(...)`
+fn unnecessary_fold_span_for_multi_element_chain() {
+    let _ = (0..3).map(|x| 2 * x).fold(false, |acc, x| acc || x > 2);
+}
+
+/// Calls which should not trigger the `UNNECESSARY_FOLD` lint
+fn unnecessary_fold_should_ignore() {
+    let _ = (0..3).fold(true, |acc, x| acc || x > 2);
+    let _ = (0..3).fold(false, |acc, x| acc && x > 2);
+    let _ = (0..3).fold(1, |acc, x| acc + x);
+    let _ = (0..3).fold(0, |acc, x| acc * x);
+    let _ = (0..3).fold(0, |acc, x| 1 + acc + x);
+
+    // We only match against an accumulator on the left
+    // hand side. We could lint for .sum and .product when
+    // it's on the right, but don't for now (and this wouldn't
+    // be valid if we extended the lint to cover arbitrary numeric
+    // types).
+    let _ = (0..3).fold(false, |acc, x| x > 2 || acc);
+    let _ = (0..3).fold(true, |acc, x| x > 2 && acc);
+    let _ = (0..3).fold(0, |acc, x| x + acc);
+    let _ = (0..3).fold(1, |acc, x| x * acc);
+}
+
 #[allow(similar_names)]
 fn main() {
     let opt = Some(0);

tests/ui/methods.stderr

@@ -493,13 +493,45 @@ error: called `skip(x).next()` on an iterator. This is more succinctly expressed
 382 |     let _ = &some_vec[..].iter().skip(3).next();
     |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: used unwrap() on an Option value. If you don't want to handle the None case gracefully, consider using expect() to provide a better panic message
-   --> $DIR/methods.rs:391:13
+error: this `.fold` can be written more succinctly using another method
+   --> $DIR/methods.rs:391:19
     |
-391 |     let _ = opt.unwrap();
+391 |     let _ = (0..3).fold(false, |acc, x| acc || x > 2);
+    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `.any(|x| x > 2)`
+    |
+    = note: `-D unnecessary-fold` implied by `-D warnings`
+
+error: this `.fold` can be written more succinctly using another method
+   --> $DIR/methods.rs:393:19
+    |
+393 |     let _ = (0..3).fold(true, |acc, x| acc && x > 2);
+    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `.all(|x| x > 2)`
+
+error: this `.fold` can be written more succinctly using another method
+   --> $DIR/methods.rs:395:19
+    |
+395 |     let _ = (0..3).fold(0, |acc, x| acc + x);
+    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `.sum()`
+
+error: this `.fold` can be written more succinctly using another method
+   --> $DIR/methods.rs:397:19
+    |
+397 |     let _ = (0..3).fold(1, |acc, x| acc * x);
+    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `.product()`
+
+error: this `.fold` can be written more succinctly using another method
+   --> $DIR/methods.rs:402:34
+    |
+402 |     let _ = (0..3).map(|x| 2 * x).fold(false, |acc, x| acc || x > 2);
+    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `.any(|x| x > 2)`
+
+error: used unwrap() on an Option value. If you don't want to handle the None case gracefully, consider using expect() to provide a better panic message
+   --> $DIR/methods.rs:427:13
+    |
+427 |     let _ = opt.unwrap();
     |             ^^^^^^^^^^^^
     |
     = note: `-D option-unwrap-used` implied by `-D warnings`
 
-error: aborting due to 66 previous errors
+error: aborting due to 71 previous errors