Rollup merge of #105332 - estebank:iterator-chains, r=oli-obk

Point out the type of associated types in every method call of iterator chains

Partially address #105184 by pointing out the type of associated types in every method call of iterator chains:

```
note: the expression is of type `Map<std::slice::Iter<'_, {integer}>, [closure@src/test/ui/iterators/invalid-iterator-chain.rs:12:18: 12:21]>`
    --> src/test/ui/iterators/invalid-iterator-chain.rs:12:14
     |
10   |         vec![0, 1]
     |         ---------- this expression has type `Vec<{integer}>`
11   |             .iter()
     |              ------ associated type `std::iter::Iterator::Item` is `&{integer}` here
12   |             .map(|x| { x; })
     |              ^^^^^^^^^^^^^^^ associated type `std::iter::Iterator::Item` is `()` here
```

We also reduce the number of impls we mention when any of the candidates is an "exact match". This benefits the output of cases with numerics greatly.

Outstanding work would be to provide a structured suggestion for appropriate changes, like in this case detecting the spurious `;` in the closure.

6 files changed, 48 insertions, 42 deletions

diff --git a/src/test/ui/issues/issue-20162.stderr b/src/test/ui/issues/issue-20162.stderr
index 3f9b3be9851..d70bf6e1d92 100644
--- a/src/test/ui/issues/issue-20162.stderr
+++ b/src/test/ui/issues/issue-20162.stderr
@@ -1,10 +1,8 @@
 error[E0277]: the trait bound `X: Ord` is not satisfied
-  --> $DIR/issue-20162.rs:5:5
+  --> $DIR/issue-20162.rs:5:7
    |
 LL |     b.sort();
-   |     ^ ---- required by a bound introduced by this call
-   |     |
-   |     the trait `Ord` is not implemented for `X`
+   |       ^^^^ the trait `Ord` is not implemented for `X`
    |
 note: required by a bound in `slice::<impl [T]>::sort`
   --> $SRC_DIR/alloc/src/slice.rs:LL:COL
diff --git a/src/test/ui/issues/issue-31173.rs b/src/test/ui/issues/issue-31173.rs
index 04efa27189b..f678df5b42b 100644
--- a/src/test/ui/issues/issue-31173.rs
+++ b/src/test/ui/issues/issue-31173.rs
@@ -4,12 +4,11 @@ pub fn get_tok(it: &mut IntoIter<u8>) {
     let mut found_e = false;
 
     let temp: Vec<u8> = it
-        //~^ ERROR to be an iterator that yields `&_`, but it yields `u8`
         .take_while(|&x| {
             found_e = true;
             false
         })
-        .cloned()
+        .cloned() //~ ERROR to be an iterator that yields `&_`, but it yields `u8`
         .collect(); //~ ERROR the method
 }
 
diff --git a/src/test/ui/issues/issue-31173.stderr b/src/test/ui/issues/issue-31173.stderr
index 58d9b564427..62d841f3789 100644
--- a/src/test/ui/issues/issue-31173.stderr
+++ b/src/test/ui/issues/issue-31173.stderr
@@ -1,16 +1,8 @@
-error[E0271]: expected `TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]>` to be an iterator that yields `&_`, but it yields `u8`
-  --> $DIR/issue-31173.rs:6:25
-   |
-LL |       let temp: Vec<u8> = it
-   |  _________________________^
-LL | |
-LL | |         .take_while(|&x| {
-LL | |             found_e = true;
-LL | |             false
-LL | |         })
-   | |__________^ expected reference, found `u8`
-LL |           .cloned()
-   |            ------ required by a bound introduced by this call
+error[E0271]: expected `TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>` to be an iterator that yields `&_`, but it yields `u8`
+  --> $DIR/issue-31173.rs:11:10
+   |
+LL |         .cloned()
+   |          ^^^^^^ expected reference, found `u8`
    |
    = note: expected reference `&_`
                    found type `u8`
@@ -20,11 +12,11 @@ note: required by a bound in `cloned`
 LL |         Self: Sized + Iterator<Item = &'a T>,
    |                                ^^^^^^^^^^^^ required by this bound in `Iterator::cloned`
 
-error[E0599]: the method `collect` exists for struct `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]>>`, but its trait bounds were not satisfied
-  --> $DIR/issue-31173.rs:13:10
+error[E0599]: the method `collect` exists for struct `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>>`, but its trait bounds were not satisfied
+  --> $DIR/issue-31173.rs:12:10
    |
 LL |         .collect();
-   |          ^^^^^^^ method cannot be called on `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]>>` due to unsatisfied trait bounds
+   |          ^^^^^^^ method cannot be called on `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>>` due to unsatisfied trait bounds
    |
   ::: $SRC_DIR/core/src/iter/adapters/take_while.rs:LL:COL
    |
@@ -37,10 +29,10 @@ LL | pub struct Cloned<I> {
    | -------------------- doesn't satisfy `_: Iterator`
    |
    = note: the following trait bounds were not satisfied:
-           `<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]> as Iterator>::Item = &_`
-           which is required by `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]>>: Iterator`
-           `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]>>: Iterator`
-           which is required by `&mut Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:8:21: 8:25]>>: Iterator`
+           `<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]> as Iterator>::Item = &_`
+           which is required by `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>>: Iterator`
+           `Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>>: Iterator`
+           which is required by `&mut Cloned<TakeWhile<&mut std::vec::IntoIter<u8>, [closure@$DIR/issue-31173.rs:7:21: 7:25]>>: Iterator`
 
 error: aborting due to 2 previous errors
 
diff --git a/src/test/ui/issues/issue-33941.stderr b/src/test/ui/issues/issue-33941.stderr
index c28986a2985..73a9b786fe2 100644
--- a/src/test/ui/issues/issue-33941.stderr
+++ b/src/test/ui/issues/issue-33941.stderr
@@ -1,10 +1,8 @@
 error[E0271]: expected `std::collections::hash_map::Iter<'_, _, _>` to be an iterator that yields `&_`, but it yields `(&_, &_)`
-  --> $DIR/issue-33941.rs:6:14
+  --> $DIR/issue-33941.rs:6:36
    |
 LL |     for _ in HashMap::new().iter().cloned() {}
-   |              ^^^^^^^^^^^^^^^^^^^^^ ------ required by a bound introduced by this call
-   |              |
-   |              expected reference, found tuple
+   |                                    ^^^^^^ expected reference, found tuple
    |
    = note: expected reference `&_`
                   found tuple `(&_, &_)`
diff --git a/src/test/ui/issues/issue-34334.stderr b/src/test/ui/issues/issue-34334.stderr
index 3188cd80cca..b610e5c1366 100644
--- a/src/test/ui/issues/issue-34334.stderr
+++ b/src/test/ui/issues/issue-34334.stderr
@@ -13,15 +13,23 @@ LL |     let sr: Vec<(u32, _, _)> = vec![];
    |                            +
 
 error[E0277]: a value of type `Vec<(u32, _, _)>` cannot be built from an iterator over elements of type `()`
-  --> $DIR/issue-34334.rs:5:33
+  --> $DIR/issue-34334.rs:5:87
    |
 LL |     let sr2: Vec<(u32, _, _)> = sr.iter().map(|(faction, th_sender, th_receiver)| {}).collect();
-   |                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ------- required by a bound introduced by this call
-   |                                 |
-   |                                 value of type `Vec<(u32, _, _)>` cannot be built from `std::iter::Iterator<Item=()>`
+   |                                                                                       ^^^^^^^ value of type `Vec<(u32, _, _)>` cannot be built from `std::iter::Iterator<Item=()>`
    |
    = help: the trait `FromIterator<()>` is not implemented for `Vec<(u32, _, _)>`
    = help: the trait `FromIterator<T>` is implemented for `Vec<T>`
+note: the method call chain might not have had the expected associated types
+  --> $DIR/issue-34334.rs:5:43
+   |
+LL |     let sr: Vec<(u32, _, _) = vec![];
+   |                               ------ this expression has type `Vec<(_, _, _)>`
+...
+LL |     let sr2: Vec<(u32, _, _)> = sr.iter().map(|(faction, th_sender, th_receiver)| {}).collect();
+   |                                    ------ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Iterator::Item` changed to `()` here
+   |                                    |
+   |                                    `Iterator::Item` is `&(_, _, _)` here
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
    |
diff --git a/src/test/ui/issues/issue-66923-show-error-for-correct-call.stderr b/src/test/ui/issues/issue-66923-show-error-for-correct-call.stderr
index ce38c3320bb..c6352978613 100644
--- a/src/test/ui/issues/issue-66923-show-error-for-correct-call.stderr
+++ b/src/test/ui/issues/issue-66923-show-error-for-correct-call.stderr
@@ -1,13 +1,18 @@
 error[E0277]: a value of type `Vec<f64>` cannot be built from an iterator over elements of type `&f64`
-  --> $DIR/issue-66923-show-error-for-correct-call.rs:8:24
+  --> $DIR/issue-66923-show-error-for-correct-call.rs:8:39
    |
 LL |     let x2: Vec<f64> = x1.into_iter().collect();
-   |                        ^^^^^^^^^^^^^^ ------- required by a bound introduced by this call
-   |                        |
-   |                        value of type `Vec<f64>` cannot be built from `std::iter::Iterator<Item=&f64>`
+   |                                       ^^^^^^^ value of type `Vec<f64>` cannot be built from `std::iter::Iterator<Item=&f64>`
    |
    = help: the trait `FromIterator<&f64>` is not implemented for `Vec<f64>`
    = help: the trait `FromIterator<T>` is implemented for `Vec<T>`
+note: the method call chain might not have had the expected associated types
+  --> $DIR/issue-66923-show-error-for-correct-call.rs:8:27
+   |
+LL |     let x1: &[f64] = &v;
+   |                      -- this expression has type `&Vec<f64>`
+LL |     let x2: Vec<f64> = x1.into_iter().collect();
+   |                           ^^^^^^^^^^^ `Iterator::Item` is `&f64` here
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
    |
@@ -15,15 +20,21 @@ LL |     fn collect<B: FromIterator<Self::Item>>(self) -> B
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Iterator::collect`
 
 error[E0277]: a value of type `Vec<f64>` cannot be built from an iterator over elements of type `&f64`
-  --> $DIR/issue-66923-show-error-for-correct-call.rs:12:14
+  --> $DIR/issue-66923-show-error-for-correct-call.rs:12:29
    |
 LL |     let x3 = x1.into_iter().collect::<Vec<f64>>();
-   |              ^^^^^^^^^^^^^^ ------- required by a bound introduced by this call
-   |              |
-   |              value of type `Vec<f64>` cannot be built from `std::iter::Iterator<Item=&f64>`
+   |                             ^^^^^^^ value of type `Vec<f64>` cannot be built from `std::iter::Iterator<Item=&f64>`
    |
    = help: the trait `FromIterator<&f64>` is not implemented for `Vec<f64>`
    = help: the trait `FromIterator<T>` is implemented for `Vec<T>`
+note: the method call chain might not have had the expected associated types
+  --> $DIR/issue-66923-show-error-for-correct-call.rs:12:17
+   |
+LL |     let x1: &[f64] = &v;
+   |                      -- this expression has type `&Vec<f64>`
+...
+LL |     let x3 = x1.into_iter().collect::<Vec<f64>>();
+   |                 ^^^^^^^^^^^ `Iterator::Item` is `&f64` here
 note: required by a bound in `collect`
   --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
    |