Provide more context on derived obligation error primary label

Expand the primary span of E0277 when the immediate unmet bound is not what the user wrote:

```
error[E0277]: the trait bound `i32: Bar` is not satisfied
 --> f100.rs:6:6
  |
6 |     <i32 as Foo>::foo();
  |      ^^^ the trait `Bar` is not implemented for `i32`, which is required by `i32: Foo`
  |
help: this trait has no implementations, consider adding one
 --> f100.rs:2:1
  |
2 | trait Bar {}
  | ^^^^^^^^^
note: required for `i32` to implement `Foo`
 --> f100.rs:3:14
  |
3 | impl<T: Bar> Foo for T {}
  |         ---  ^^^     ^
  |         |
  |         unsatisfied trait bound introduced here
```

Fix #40120.

2 files changed, 28 insertions, 28 deletions

diff --git a/tests/ui/errors/trait-bound-error-spans/blame-trait-error.stderr b/tests/ui/errors/trait-bound-error-spans/blame-trait-error.stderr
index 9228a047e87..bd4e9348227 100644
--- a/tests/ui/errors/trait-bound-error-spans/blame-trait-error.stderr
+++ b/tests/ui/errors/trait-bound-error-spans/blame-trait-error.stderr
@@ -2,7 +2,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:53:46
    |
 LL |     want(Wrapper { value: Burrito { filling: q } });
-   |     ----                                     ^ the trait `T3` is not implemented for `Q`
+   |     ----                                     ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<Burrito<Q>>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -38,7 +38,7 @@ LL |     want(Some(()));
    |     |
    |     required by a bound introduced by this call
    |
-   = help: the trait `Iterator` is not implemented for `()`
+   = help: the trait `Iterator` is not implemented for `()`, which is required by `Option<()>: T1`
    = help: the trait `T1` is implemented for `Option<It>`
 note: required for `Option<()>` to implement `T1`
   --> $DIR/blame-trait-error.rs:21:20
@@ -109,7 +109,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:65:45
    |
 LL |     want(&ExampleTuple::ExampleTupleVariant(q));
-   |     ----                                    ^ the trait `T3` is not implemented for `Q`
+   |     ----                                    ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleTuple<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -134,7 +134,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:68:31
    |
 LL |     want(&ExampleTupleVariant(q));
-   |     ----                      ^ the trait `T3` is not implemented for `Q`
+   |     ----                      ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleTuple<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -159,7 +159,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:71:50
    |
 LL |     want(&ExampleOtherTuple::ExampleTupleVariant(q));
-   |     ----                                         ^ the trait `T3` is not implemented for `Q`
+   |     ----                                         ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleTuple<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -184,7 +184,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:74:44
    |
 LL |     want(&ExampleDifferentTupleVariantName(q));
-   |     ----                                   ^ the trait `T3` is not implemented for `Q`
+   |     ----                                   ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleTuple<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -209,7 +209,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:77:45
    |
 LL |     want(&ExampleYetAnotherTupleVariantName(q));
-   |     ----                                    ^ the trait `T3` is not implemented for `Q`
+   |     ----                                    ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleTuple<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -234,7 +234,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:80:56
    |
 LL |     want(&ExampleStruct::ExampleStructVariant { field: q });
-   |     ---- required by a bound introduced by this call   ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call   ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleStruct<Q>: T1`
    |
 note: required for `ExampleStruct<Q>` to implement `T1`
   --> $DIR/blame-trait-error.rs:45:9
@@ -257,7 +257,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:83:41
    |
 LL |     want(&ExampleStructVariant { field: q });
-   |     ----                                ^ the trait `T3` is not implemented for `Q`
+   |     ----                                ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleStruct<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -282,7 +282,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:86:61
    |
 LL |     want(&ExampleOtherStruct::ExampleStructVariant { field: q });
-   |     ---- required by a bound introduced by this call        ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call        ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleStruct<Q>: T1`
    |
 note: required for `ExampleStruct<Q>` to implement `T1`
   --> $DIR/blame-trait-error.rs:45:9
@@ -305,7 +305,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:89:54
    |
 LL |     want(&ExampleDifferentStructVariantName { field: q });
-   |     ---- required by a bound introduced by this call ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleStruct<Q>: T1`
    |
 note: required for `ExampleStruct<Q>` to implement `T1`
   --> $DIR/blame-trait-error.rs:45:9
@@ -328,7 +328,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:92:55
    |
 LL |     want(&ExampleYetAnotherStructVariantName { field: q });
-   |     ---- required by a bound introduced by this call  ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call  ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleStruct<Q>: T1`
    |
 note: required for `ExampleStruct<Q>` to implement `T1`
   --> $DIR/blame-trait-error.rs:45:9
@@ -351,7 +351,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:95:38
    |
 LL |     want(&ExampleActuallyTupleStruct(q, 0));
-   |     ----                             ^ the trait `T3` is not implemented for `Q`
+   |     ----                             ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleActuallyTupleStruct<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -376,7 +376,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error.rs:98:43
    |
 LL |     want(&ExampleActuallyTupleStructOther(q, 0));
-   |     ----                                  ^ the trait `T3` is not implemented for `Q`
+   |     ----                                  ^ the trait `T3` is not implemented for `Q`, which is required by `&ExampleActuallyTupleStruct<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
diff --git a/tests/ui/errors/traits/blame-trait-error-spans-on-exprs.stderr b/tests/ui/errors/traits/blame-trait-error-spans-on-exprs.stderr
index b6a24e12bcc..a2df6843f43 100644
--- a/tests/ui/errors/traits/blame-trait-error-spans-on-exprs.stderr
+++ b/tests/ui/errors/traits/blame-trait-error-spans-on-exprs.stderr
@@ -2,7 +2,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:81:60
    |
 LL |     want(Wrapper { value: Burrito { spicy: false, filling: q } });
-   |     ---- required by a bound introduced by this call       ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call       ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<Burrito<Q>>: T1`
    |
 note: required for `Burrito<Q>` to implement `T2`
   --> $DIR/blame-trait-error-spans-on-exprs.rs:22:13
@@ -32,7 +32,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:85:84
    |
 LL |     want(Wrapper { value: BurritoKinds::SmallBurrito { spicy: true, small_filling: q } });
-   |     ---- required by a bound introduced by this call                               ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call                               ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<BurritoKinds<Q>>: T1`
    |
 note: required for `BurritoKinds<Q>` to implement `T2`
   --> $DIR/blame-trait-error-spans-on-exprs.rs:32:13
@@ -62,7 +62,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:89:39
    |
 LL |     want(Wrapper { value: Taco(false, q) });
-   |     ----                              ^ the trait `T3` is not implemented for `Q`
+   |     ----                              ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<Taco<Q>>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -94,7 +94,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:93:53
    |
 LL |     want(Wrapper { value: TacoKinds::OneTaco(false, q) });
-   |     ----                                            ^ the trait `T3` is not implemented for `Q`
+   |     ----                                            ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<TacoKinds<Q>>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -126,7 +126,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:97:74
    |
 LL |     want(Wrapper { value: GenericBurrito { spiciness: NotSpicy, filling: q } });
-   |     ---- required by a bound introduced by this call                     ^ the trait `T3` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call                     ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<GenericBurrito<NotSpicy, Q>>: T1`
    |
 note: required for `GenericBurrito<NotSpicy, Q>` to implement `T2`
   --> $DIR/blame-trait-error-spans-on-exprs.rs:47:16
@@ -156,7 +156,7 @@ error[E0277]: the trait bound `Q: T2` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:101:14
    |
 LL |     want((3, q));
-   |     ----     ^ the trait `T2` is not implemented for `Q`
+   |     ----     ^ the trait `T2` is not implemented for `Q`, which is required by `({integer}, Q): T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -181,7 +181,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:105:31
    |
 LL |     want(Wrapper { value: (3, q) });
-   |     ----                      ^ the trait `T3` is not implemented for `Q`
+   |     ----                      ^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<({integer}, Q)>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -213,7 +213,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:109:15
    |
 LL |     want(((3, q), 5));
-   |     ----      ^ the trait `T3` is not implemented for `Q`
+   |     ----      ^ the trait `T3` is not implemented for `Q`, which is required by `(({integer}, Q), {integer}): T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -245,7 +245,7 @@ error[E0277]: the trait bound `Q: T1` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:112:49
    |
 LL |     want(DoubleWrapper { item: Wrapper { value: q } });
-   |     ----                                        ^ the trait `T1` is not implemented for `Q`
+   |     ----                                        ^ the trait `T1` is not implemented for `Q`, which is required by `DoubleWrapper<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -270,7 +270,7 @@ error[E0277]: the trait bound `Q: T1` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:115:88
    |
 LL |     want(DoubleWrapper { item: Wrapper { value: DoubleWrapper { item: Wrapper { value: q } } } });
-   |     ---- required by a bound introduced by this call                                   ^ the trait `T1` is not implemented for `Q`
+   |     ---- required by a bound introduced by this call                                   ^ the trait `T1` is not implemented for `Q`, which is required by `DoubleWrapper<DoubleWrapper<Q>>: T1`
    |
 note: required for `DoubleWrapper<Q>` to implement `T1`
   --> $DIR/blame-trait-error-spans-on-exprs.rs:72:13
@@ -295,7 +295,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:119:27
    |
 LL |     want(Wrapper { value: AliasBurrito { spiciness: q, filling: q } });
-   |     ----                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `T3` is not implemented for `Q`
+   |     ----                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `T3` is not implemented for `Q`, which is required by `Wrapper<GenericBurrito<Q, Q>>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -327,7 +327,7 @@ error[E0277]: the trait bound `Q: T1` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:122:35
    |
 LL |     want(Two { a: Two { a: (), b: q }, b: () });
-   |     ----                          ^ the trait `T1` is not implemented for `Q`
+   |     ----                          ^ the trait `T1` is not implemented for `Q`, which is required by `Two<Two<(), Q>, ()>: T1`
    |     |
    |     required by a bound introduced by this call
    |
@@ -354,7 +354,7 @@ error[E0277]: the trait bound `Q: T1` is not satisfied
 LL |     want(
    |     ---- required by a bound introduced by this call
 LL |         Two { a: Two { a: (), b: Two { a: Two { a: (), b: q }, b: () } }, b: () },
-   |                                                           ^ the trait `T1` is not implemented for `Q`
+   |                                                           ^ the trait `T1` is not implemented for `Q`, which is required by `Two<Two<(), Two<Two<(), Q>, ()>>, ()>: T1`
    |
 note: required for `Two<Two<(), Q>, ()>` to implement `T1`
   --> $DIR/blame-trait-error-spans-on-exprs.rs:66:19
@@ -379,7 +379,7 @@ error[E0277]: the trait bound `Q: T3` is not satisfied
   --> $DIR/blame-trait-error-spans-on-exprs.rs:133:44
    |
 LL |     want(&Burrito { spicy: false, filling: q });
-   |     ----                                   ^ the trait `T3` is not implemented for `Q`
+   |     ----                                   ^ the trait `T3` is not implemented for `Q`, which is required by `&Burrito<Q>: T1`
    |     |
    |     required by a bound introduced by this call
    |