Rollup merge of #152103 - eggyal:caught-divergence-not-unused, r=cjgillot

Consider captures to be used by closures that unwind

Assignments to a captured variable within a diverging closure should not be considered unused if the divergence is caught.

This patch considers such assignments/captures to be used by diverging closures irrespective of whether the divergence is caught, but better a false negative unused lint than a false positive one (the latter having caused a stable-to-stable regression).

Fixes #152079
r? compiler

Author: jhpratt

compiler/rustc_mir_transform/src/liveness.rs

@@ -1291,6 +1291,7 @@ impl<'tcx> Visitor<'tcx> for TransferFunction<'_, 'tcx> {
             TerminatorKind::Return
             | TerminatorKind::Yield { .. }
             | TerminatorKind::Goto { target: START_BLOCK } // Inserted for the `FnMut` case.
+            | TerminatorKind::Call { target: None, .. } // unwinding could be caught
                 if self.capture_kind != CaptureKind::None =>
             {
                 // All indirect captures have an effect on the environment, so we mark them as live.

tests/ui/lint/unused/diverging-path.rs

@@ -0,0 +1,21 @@
+//! Assignments to a captured variable within a diverging closure should not be considered unused if
+//! the divergence is caught.
+//!
+//! Regression test for https://github.com/rust-lang/rust/issues/152079
+//@ compile-flags: -Wunused
+//@ check-pass
+
+fn main() {
+    let mut x = 1;
+    catch(|| {
+        x = 2;
+        panic!();
+    });
+    dbg!(x);
+}
+
+fn catch<F: FnOnce()>(f: F) {
+    if let Ok(true) = std::fs::exists("may_or_may_not_call_f") {
+        _ = std::panic::catch_unwind(std::panic::AssertUnwindSafe(f));
+    }
+}