Rollup merge of #106740 - petar-dambovaliev:float-iterator-hint, r=Nilstrieb

Adding a hint on iterator type errors

Issue reference https://github.com/rust-lang/rust/issues/106728

- [x] add a case in the attribute
- [x] add a test

closes #106728

4 files changed, 34 insertions, 0 deletions

diff --git a/library/core/src/iter/traits/iterator.rs b/library/core/src/iter/traits/iterator.rs
index 99aaf798e41..a4a665d48d5 100644
--- a/library/core/src/iter/traits/iterator.rs
+++ b/library/core/src/iter/traits/iterator.rs
@@ -58,6 +58,11 @@ fn _assert_is_object_safe(_: &dyn Iterator<Item = ()>) {}
         note = "if you want to iterate between `start` until a value `end`, use the exclusive range \
               syntax `start..end` or the inclusive range syntax `start..=end`"
     ),
+    on(
+        _Self = "{float}",
+        note = "if you want to iterate between `start` until a value `end`, use the exclusive range \
+              syntax `start..end` or the inclusive range syntax `start..=end`"
+    ),
     label = "`{Self}` is not an iterator",
     message = "`{Self}` is not an iterator"
 )]
diff --git a/tests/ui/iterators/float_iterator_hint.rs b/tests/ui/iterators/float_iterator_hint.rs
new file mode 100644
index 00000000000..a3335ca41f7
--- /dev/null
+++ b/tests/ui/iterators/float_iterator_hint.rs
@@ -0,0 +1,15 @@
+// #106728
+
+fn main() {
+    for i in 0.2 {
+        //~^ ERROR `{float}` is not an iterator
+        //~| `{float}` is not an iterator
+        //~| NOTE in this expansion of desugaring of `for` loop
+        //~| NOTE in this expansion of desugaring of `for` loop
+        //~| NOTE in this expansion of desugaring of `for` loop
+        //~| NOTE in this expansion of desugaring of `for` loop
+        //~| NOTE if you want to iterate between `start` until a value `end`, use the exclusive range syntax `start..end` or the inclusive range syntax `start..=end`
+        //~| NOTE required for `{float}` to implement `IntoIterator`
+        println!();
+    }
+}
diff --git a/tests/ui/iterators/float_iterator_hint.stderr b/tests/ui/iterators/float_iterator_hint.stderr
new file mode 100644
index 00000000000..bae23a1f8ff
--- /dev/null
+++ b/tests/ui/iterators/float_iterator_hint.stderr
@@ -0,0 +1,13 @@
+error[E0277]: `{float}` is not an iterator
+  --> $DIR/float_iterator_hint.rs:4:14
+   |
+LL |     for i in 0.2 {
+   |              ^^^ `{float}` is not an iterator
+   |
+   = help: the trait `Iterator` is not implemented for `{float}`
+   = note: if you want to iterate between `start` until a value `end`, use the exclusive range syntax `start..end` or the inclusive range syntax `start..=end`
+   = note: required for `{float}` to implement `IntoIterator`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/iterators/integral.stderr b/tests/ui/iterators/integral.stderr
index 047a71f98d9..c142fec8da0 100644
--- a/tests/ui/iterators/integral.stderr
+++ b/tests/ui/iterators/integral.stderr
@@ -115,6 +115,7 @@ LL |     for _ in 42.0 {}
    |              ^^^^ `{float}` is not an iterator
    |
    = help: the trait `Iterator` is not implemented for `{float}`
+   = note: if you want to iterate between `start` until a value `end`, use the exclusive range syntax `start..end` or the inclusive range syntax `start..=end`
    = note: required for `{float}` to implement `IntoIterator`
 
 error: aborting due to 12 previous errors