Rollup merge of #88578 - notriddle:notriddle/suggest-add-reference-to-for-loop-iter, r=nagisa

fix(rustc): suggest `items` be borrowed in `for i in items[x..]`

Fixes #87994

3 files changed, 92 insertions, 2 deletions

diff --git a/src/test/ui/issues/issue-20605.stderr b/src/test/ui/issues/issue-20605.stderr
index 25a90df4561..ce3ab6b5998 100644
--- a/src/test/ui/issues/issue-20605.stderr
+++ b/src/test/ui/issues/issue-20605.stderr
@@ -2,9 +2,12 @@ error[E0277]: the size for values of type `dyn Iterator<Item = &'a mut u8>` cann
   --> $DIR/issue-20605.rs:2:17
    |
 LL |     for item in *things { *item = 0 }
-   |                 ^^^^^^^ doesn't have a size known at compile-time
+   |                 ^^^^^^^
+   |                 |
+   |                 expected an implementor of trait `IntoIterator`
+   |                 help: consider mutably borrowing here: `&mut *things`
    |
-   = help: the trait `Sized` is not implemented for `dyn Iterator<Item = &'a mut u8>`
+   = note: the trait bound `dyn Iterator<Item = &'a mut u8>: IntoIterator` is not satisfied
    = note: required because of the requirements on the impl of `IntoIterator` for `dyn Iterator<Item = &'a mut u8>`
 note: required by `into_iter`
   --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
diff --git a/src/test/ui/suggestions/slice-issue-87994.rs b/src/test/ui/suggestions/slice-issue-87994.rs
new file mode 100644
index 00000000000..ecb7f54ea25
--- /dev/null
+++ b/src/test/ui/suggestions/slice-issue-87994.rs
@@ -0,0 +1,16 @@
+fn main() {
+  let v = vec![1i32, 2, 3];
+  for _ in v[1..] {
+    //~^ ERROR [i32]` is not an iterator [E0277]
+    //~^^ ERROR known at compilation time
+  }
+  struct K {
+    n: i32,
+  }
+  let mut v2 = vec![K { n: 1 }, K { n: 1 }, K { n: 1 }];
+  for i2 in v2[1..] {
+    //~^ ERROR [K]` is not an iterator [E0277]
+    //~^^ ERROR known at compilation time
+    i2.n = 2;
+  }
+}
diff --git a/src/test/ui/suggestions/slice-issue-87994.stderr b/src/test/ui/suggestions/slice-issue-87994.stderr
new file mode 100644
index 00000000000..018f62e783d
--- /dev/null
+++ b/src/test/ui/suggestions/slice-issue-87994.stderr
@@ -0,0 +1,71 @@
+error[E0277]: the size for values of type `[i32]` cannot be known at compilation time
+  --> $DIR/slice-issue-87994.rs:3:12
+   |
+LL |   for _ in v[1..] {
+   |            ^^^^^^
+   |            |
+   |            expected an implementor of trait `IntoIterator`
+   |            help: consider borrowing here: `&v[1..]`
+   |
+   = note: the trait bound `[i32]: IntoIterator` is not satisfied
+   = note: required because of the requirements on the impl of `IntoIterator` for `[i32]`
+note: required by `into_iter`
+  --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
+   |
+LL |     fn into_iter(self) -> Self::IntoIter;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: `[i32]` is not an iterator
+  --> $DIR/slice-issue-87994.rs:3:12
+   |
+LL |   for _ in v[1..] {
+   |            ^^^^^^
+   |            |
+   |            expected an implementor of trait `IntoIterator`
+   |            help: consider borrowing here: `&v[1..]`
+   |
+   = note: the trait bound `[i32]: IntoIterator` is not satisfied
+   = note: required because of the requirements on the impl of `IntoIterator` for `[i32]`
+note: required by `into_iter`
+  --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
+   |
+LL |     fn into_iter(self) -> Self::IntoIter;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the size for values of type `[K]` cannot be known at compilation time
+  --> $DIR/slice-issue-87994.rs:11:13
+   |
+LL |   for i2 in v2[1..] {
+   |             ^^^^^^^
+   |             |
+   |             expected an implementor of trait `IntoIterator`
+   |             help: consider borrowing here: `&v2[1..]`
+   |
+   = note: the trait bound `[K]: IntoIterator` is not satisfied
+   = note: required because of the requirements on the impl of `IntoIterator` for `[K]`
+note: required by `into_iter`
+  --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
+   |
+LL |     fn into_iter(self) -> Self::IntoIter;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: `[K]` is not an iterator
+  --> $DIR/slice-issue-87994.rs:11:13
+   |
+LL |   for i2 in v2[1..] {
+   |             ^^^^^^^
+   |             |
+   |             expected an implementor of trait `IntoIterator`
+   |             help: consider borrowing here: `&v2[1..]`
+   |
+   = note: the trait bound `[K]: IntoIterator` is not satisfied
+   = note: required because of the requirements on the impl of `IntoIterator` for `[K]`
+note: required by `into_iter`
+  --> $SRC_DIR/core/src/iter/traits/collect.rs:LL:COL
+   |
+LL |     fn into_iter(self) -> Self::IntoIter;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 4 previous errors
+
+For more information about this error, try `rustc --explain E0277`.