Auto merge of #117292 - estebank:issue-80446, r=davidtwco

Detect misparsed binop caused by missing semi

When encountering

```rust
foo()
*bar = baz;
```

We currently emit potentially two errors, one for the return type of
`foo` not being multiplicative by the type of `bar`, and another for
`foo() * bar` not being assignable.

We now check for this case and suggest adding a semicolon in the right
place and emit only a single error.

Fix #80446.

3 files changed, 37 insertions, 0 deletions

diff --git a/tests/ui/binop/false-binop-caused-by-missing-semi.fixed b/tests/ui/binop/false-binop-caused-by-missing-semi.fixed
new file mode 100644
index 00000000000..b47372c9064
--- /dev/null
+++ b/tests/ui/binop/false-binop-caused-by-missing-semi.fixed
@@ -0,0 +1,10 @@
+// run-rustfix
+fn foo() {}
+fn main() {
+    let mut y = 42;
+    let x = &mut y;
+    foo();
+    *x = 0;  //~ ERROR invalid left-hand side of assignment
+    let _ = x;
+    println!("{y}");
+}
diff --git a/tests/ui/binop/false-binop-caused-by-missing-semi.rs b/tests/ui/binop/false-binop-caused-by-missing-semi.rs
new file mode 100644
index 00000000000..14671de7e51
--- /dev/null
+++ b/tests/ui/binop/false-binop-caused-by-missing-semi.rs
@@ -0,0 +1,10 @@
+// run-rustfix
+fn foo() {}
+fn main() {
+    let mut y = 42;
+    let x = &mut y;
+    foo()
+    *x = 0;  //~ ERROR invalid left-hand side of assignment
+    let _ = x;
+    println!("{y}");
+}
diff --git a/tests/ui/binop/false-binop-caused-by-missing-semi.stderr b/tests/ui/binop/false-binop-caused-by-missing-semi.stderr
new file mode 100644
index 00000000000..fca042b1c57
--- /dev/null
+++ b/tests/ui/binop/false-binop-caused-by-missing-semi.stderr
@@ -0,0 +1,17 @@
+error[E0070]: invalid left-hand side of assignment
+  --> $DIR/false-binop-caused-by-missing-semi.rs:7:8
+   |
+LL | /     foo()
+LL | |     *x = 0;
+   | |      - ^
+   | |______|
+   |        cannot assign to this expression
+   |
+help: you might have meant to write a semicolon here
+   |
+LL |     foo();
+   |          +
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0070`.