Rollup merge of #107175 - compiler-errors:bad-types-in-vec-push, r=estebank

Fix escaping inference var ICE in `point_at_expr_source_of_inferred_type`

Fixes #107158

`point_at_expr_source_of_inferred_type` uses `lookup_probe` to adjust the self type of a method receiver -- but that method returns inference variables from inside a probe. That means that the ty vars are no longer valid, so we can't use any infcx methods on them.

Also, pass some extra span info to hack a quick solution to bad labels, resulting in this diagnostic improvement:

```rust
fn example2() {
    let mut x = vec![1];
    x.push("");
}
```

```diff
  error[E0308]: mismatched types
   --> src/main.rs:5:12
    |
  5 |     x.push("");
    |       ---- ^^
    |       |    |
    |       |    expected integer, found `&str`
-   |       |    this is of type `&'static str`, which causes `x` to be inferred as `Vec<{integer}>`
    |       arguments to this method are incorrect
```
(since that "which causes `x` to be inferred as `Vec<{integer}>` part is wrong)

r? `@estebank`

(we really should make this code better in general, cc #106590, but that's a bit bigger issue that needs some more thinking about)

2 files changed, 49 insertions, 0 deletions

diff --git a/tests/ui/typeck/bad-type-in-vec-push.rs b/tests/ui/typeck/bad-type-in-vec-push.rs
new file mode 100644
index 00000000000..a807f030cfc
--- /dev/null
+++ b/tests/ui/typeck/bad-type-in-vec-push.rs
@@ -0,0 +1,20 @@
+// The error message here still is pretty confusing.
+
+fn main() {
+    let mut result = vec![1];
+    // The type of `result` is constrained to be `Vec<{integer}>` here.
+    // But the logic we use to find what expression constrains a type
+    // is not sophisticated enough to know this.
+
+    let mut vector = Vec::new();
+    vector.sort();
+    result.push(vector);
+    //~^ ERROR mismatched types
+    // So it thinks that the type of `result` is constrained here.
+}
+
+fn example2() {
+    let mut x = vec![1];
+    x.push("");
+    //~^ ERROR mismatched types
+}
diff --git a/tests/ui/typeck/bad-type-in-vec-push.stderr b/tests/ui/typeck/bad-type-in-vec-push.stderr
new file mode 100644
index 00000000000..e4c99ec8e70
--- /dev/null
+++ b/tests/ui/typeck/bad-type-in-vec-push.stderr
@@ -0,0 +1,29 @@
+error[E0308]: mismatched types
+  --> $DIR/bad-type-in-vec-push.rs:11:17
+   |
+LL |     vector.sort();
+   |     ------ here the type of `vector` is inferred to be `Vec<_>`
+LL |     result.push(vector);
+   |            ---- ^^^^^^ expected integer, found struct `Vec`
+   |            |
+   |            arguments to this method are incorrect
+   |
+   = note: expected type `{integer}`
+            found struct `Vec<_>`
+note: associated function defined here
+  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
+
+error[E0308]: mismatched types
+  --> $DIR/bad-type-in-vec-push.rs:18:12
+   |
+LL |     x.push("");
+   |       ---- ^^ expected integer, found `&str`
+   |       |
+   |       arguments to this method are incorrect
+   |
+note: associated function defined here
+  --> $SRC_DIR/alloc/src/vec/mod.rs:LL:COL
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.