Fix debug infinite loop

[GuillaumeGomez]

Fixes#41338.

[rust-highfive]

r? @BurntSushi

(rust_highfive has picked a reviewer for you, use r? to override)

[sfackler]

How is this going to fix things? Isn't it just going to recurse the same way?

[GuillaumeGomez]

You give me a doubt on the fact that I tested correctly.

[GuillaumeGomez]

Fixed for good this time.

[ollie27]

Looking at #39002, the same mistake was made for the following types as well which need to be fixed:

enum_set::Iter
linked_list::Iter
linked_list::IterMut
linked_list::IntoIter
linked_list::FrontPlace
linked_list::BackPlace
vec_deque::Iter
vec_deque::IterMut
vec_deque::IntoIter
vec_deque::Drain

[ollie27]

It would be better to use f.debug_tuple("Difference").field(&self.a).field(&self.b).finish() but in this case as it's including every field, #[derive(Debug)] would suffice.

However, like other iterators in std this could use f.debug_list().entries(self.clone()).finish() to display a list of the items the iterator will return.

[GuillaumeGomez]

This seems like a better idea. Updating and testing.

[GuillaumeGomez]

Updated.

[alexcrichton]

@bors: r+

[bors]

📌 Commit a850cdc has been approved by alexcrichton

[bors]

⌛ Testing commit a850cdc with merge 4eb85e2...

[bors]

💔 Test failed - status-appveyor

[alexcrichton]

@bors: retry

• std.dll issue Spurious failure removing std.dll during tests on MSVC #41006

[bors]

⌛ Testing commit a850cdc with merge 535ee6c...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: alexcrichton
Pushing 535ee6c to master...