Fix invalid while_let_on_iterator suggestion

clippy_lints/src/utils/mod.rs

@@ -958,7 +958,16 @@ pub fn is_refutable(cx: &LateContext<'_, '_>, pat: &Pat) -> bool {
             }
         },
         PatKind::Slice(ref head, ref middle, ref tail) => {
-            are_refutable(cx, head.iter().chain(middle).chain(tail.iter()).map(|pat| &**pat))
+            match &cx.tables.node_type(pat.hir_id).sty {
+                ty::Slice(..) => {
+                    // [..] is the only irrefutable slice pattern.
+                    !head.is_empty() || middle.is_none() || !tail.is_empty()
+                },
+                _ => {
+                    // Assume it's an array.
+                    are_refutable(cx, head.iter().chain(middle).chain(tail.iter()).map(|pat| &**pat))
+                },
+            }
         },
     }
 }

tests/ui/while_loop.rs

@@ -1,5 +1,6 @@
 #![warn(clippy::while_let_loop, clippy::empty_loop, clippy::while_let_on_iterator)]
 #![allow(dead_code, clippy::never_loop, unused, clippy::cyclomatic_complexity)]
+#![feature(slice_patterns)]
 
 fn main() {
     let y = Some(true);
@@ -226,4 +227,34 @@ fn refutable() {
             let _ = elem.or_else(|| *iter.next()?);
         }
     }
+
+    // Issue 3780
+    {
+        let v = vec![1, 2, 3];
+        let mut it = v.windows(2);
+        while let Some([x, y]) = it.next() {
+            println!("x: {}", x);
+            println!("y: {}", y);
+        }
+
+        let mut it = v.windows(2);
+        while let Some([x, ..]) = it.next() {
+            println!("x: {}", x);
+        }
+
+        let mut it = v.windows(2);
+        while let Some([.., y]) = it.next() {
+            println!("y: {}", y);
+        }
+
+        let mut it = v.windows(2);
+        while let Some([..]) = it.next() {}
+
+        let v = vec![[1], [2], [3]];
+        let mut it = v.iter();
+        while let Some([1]) = it.next() {}
+
+        let mut it = v.iter();
+        while let Some([x]) = it.next() {}
+    }
 }

tests/ui/while_loop.stderr

@@ -1,5 +1,5 @@
 error: this loop could be written as a `while let` loop
-  --> $DIR/while_loop.rs:6:5
+  --> $DIR/while_loop.rs:7:5
    |
 LL | /     loop {
 LL | |         if let Some(_x) = y {
@@ -13,7 +13,7 @@ LL | |     }
    = note: `-D clippy::while-let-loop` implied by `-D warnings`
 
 error: this loop could be written as a `while let` loop
-  --> $DIR/while_loop.rs:20:5
+  --> $DIR/while_loop.rs:21:5
    |
 LL | /     loop {
 LL | |         match y {
@@ -24,7 +24,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(_x) = y { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> $DIR/while_loop.rs:26:5
+  --> $DIR/while_loop.rs:27:5
    |
 LL | /     loop {
 LL | |         let x = match y {
@@ -36,7 +36,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(x) = y { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> $DIR/while_loop.rs:34:5
+  --> $DIR/while_loop.rs:35:5
    |
 LL | /     loop {
 LL | |         let x = match y {
@@ -48,7 +48,7 @@ LL | |     }
    | |_____^ help: try: `while let Some(x) = y { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> $DIR/while_loop.rs:62:5
+  --> $DIR/while_loop.rs:63:5
    |
 LL | /     loop {
 LL | |         let (e, l) = match "".split_whitespace().next() {
@@ -60,27 +60,27 @@ LL | |     }
    | |_____^ help: try: `while let Some(word) = "".split_whitespace().next() { .. }`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_loop.rs:72:33
+  --> $DIR/while_loop.rs:73:33
    |
 LL |     while let Option::Some(x) = iter.next() {
    |                                 ^^^^^^^^^^^ help: try: `for x in iter { .. }`
    |
    = note: `-D clippy::while-let-on-iterator` implied by `-D warnings`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_loop.rs:77:25
+  --> $DIR/while_loop.rs:78:25
    |
 LL |     while let Some(x) = iter.next() {
    |                         ^^^^^^^^^^^ help: try: `for x in iter { .. }`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_loop.rs:82:25
+  --> $DIR/while_loop.rs:83:25
    |
 LL |     while let Some(_) = iter.next() {}
    |                         ^^^^^^^^^^^ help: try: `for _ in iter { .. }`
 
 error: this loop could be written as a `while let` loop
-  --> $DIR/while_loop.rs:125:5
+  --> $DIR/while_loop.rs:126:5
    |
 LL | /     loop {
 LL | |         let _ = match iter.next() {
@@ -92,24 +92,36 @@ LL | |     }
    | |_____^ help: try: `while let Some(ele) = iter.next() { .. }`
 
 error: empty `loop {}` detected. You may want to either use `panic!()` or add `std::thread::sleep(..);` to the loop body.
-  --> $DIR/while_loop.rs:130:9
+  --> $DIR/while_loop.rs:131:9
    |
 LL |         loop {}
    |         ^^^^^^^
    |
    = note: `-D clippy::empty-loop` implied by `-D warnings`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_loop.rs:188:29
+  --> $DIR/while_loop.rs:189:29
    |
 LL |         while let Some(v) = y.next() {
    |                             ^^^^^^^^ help: try: `for v in y { .. }`
 
 error: this loop could be written as a `for` loop
-  --> $DIR/while_loop.rs:216:26
+  --> $DIR/while_loop.rs:217:26
    |
 LL |     while let Some(..) = values.iter().next() {
    |                          ^^^^^^^^^^^^^^^^^^^^ help: try: `for _ in values.iter() { .. }`
 
-error: aborting due to 12 previous errors
+error: this loop could be written as a `for` loop
+  --> $DIR/while_loop.rs:251:32
+   |
+LL |         while let Some([..]) = it.next() {}
+   |                                ^^^^^^^^^ help: try: `for [..] in it { .. }`
+
+error: this loop could be written as a `for` loop
+  --> $DIR/while_loop.rs:258:31
+   |
+LL |         while let Some([x]) = it.next() {}
+   |                               ^^^^^^^^^ help: try: `for [x] in it { .. }`
+
+error: aborting due to 14 previous errors