Rollup merge of rust-lang#129340 - stephen-lazaro:u/slazaro/issue-129274, r=compiler-errors

Remove Duplicate E0381 Label

Aims to resolve rust-lang#129274, and adds a test for the case.

Essentially, we are duplicating this span for some reason. For now, I'm just using a set to collect the spans rather than the vec. I imagine there's probably no real reason to inspect duplicates in this area, but if I'm wrong I can adjust to collect "seen spans" in just the point where this label is applied.

I'm not sure why it's producing duplicate spans. Looks like this has been this way for a while? I think it gives the duplicate label on 1.75.0 for example.

Author: matthiaskrgr

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -678,14 +678,15 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, '_, 'infcx, 'tcx> {
         let inits = &self.move_data.init_path_map[mpi];
         let move_path = &self.move_data.move_paths[mpi];
         let decl_span = self.body.local_decls[move_path.place.local].source_info.span;
-        let mut spans = vec![];
+        let mut spans_set = FxIndexSet::default();
         for init_idx in inits {
             let init = &self.move_data.inits[*init_idx];
             let span = init.span(self.body);
             if !span.is_dummy() {
-                spans.push(span);
+                spans_set.insert(span);
             }
         }
+        let spans: Vec<_> = spans_set.into_iter().collect();
 
         let (name, desc) = match self.describe_place_with_options(
             moved_place,

tests/ui/duplicate-label-E0381-issue-129274.rs

@@ -0,0 +1,13 @@
+fn main() {
+    fn test() {
+        loop {
+            let blah: Option<String>;
+            if true {
+                blah = Some("".to_string());
+            }
+            if let Some(blah) = blah.as_ref() { //~ ERROR E0381
+            }
+        }
+    }
+    println!("{:?}", test())
+}

tests/ui/duplicate-label-E0381-issue-129274.stderr

@@ -0,0 +1,15 @@
+error[E0381]: used binding `blah` is possibly-uninitialized
+  --> $DIR/duplicate-label-E0381-issue-129274.rs:8:33
+   |
+LL |             let blah: Option<String>;
+   |                 ---- binding declared here but left uninitialized
+LL |             if true {
+LL |                 blah = Some("".to_string());
+   |                 ---- binding initialized here in some conditions
+LL |             }
+LL |             if let Some(blah) = blah.as_ref() {
+   |                                 ^^^^ `blah` used here but it is possibly-uninitialized
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0381`.