Auto merge of #131326 - dingxiangfei2009:issue-130836-attempt-2, r=nikomatsakis

Reduce false positives of tail-expr-drop-order from consumed values (attempt #2)

r? `@nikomatsakis`

Tracked by #123739.

Related to #129864 but not replacing, yet.

Related to #130836.

This is an implementation of the approach suggested in the [Zulip stream](https://rust-lang.zulipchat.com/#narrow/stream/213817-t-lang/topic/temporary.20drop.20order.20changes). A new MIR statement `BackwardsIncompatibleDrop` is added to the MIR syntax. The lint now works by inspecting possibly live move paths before at the `BackwardsIncompatibleDrop` location and the actual drop under the current edition, which should be one before Edition 2024 in practice.

1 files changed, 5 insertions, 0 deletions

diff --git a/compiler/rustc_middle/src/mir/pretty.rs b/compiler/rustc_middle/src/mir/pretty.rs
index f0e2b7a376c..2bfcd0a6227 100644
--- a/compiler/rustc_middle/src/mir/pretty.rs
+++ b/compiler/rustc_middle/src/mir/pretty.rs
@@ -834,6 +834,11 @@ impl Debug for Statement<'_> {
             Intrinsic(box ref intrinsic) => write!(fmt, "{intrinsic}"),
             ConstEvalCounter => write!(fmt, "ConstEvalCounter"),
             Nop => write!(fmt, "nop"),
+            BackwardIncompatibleDropHint { ref place, reason: _ } => {
+                // For now, we don't record the reason because there is only one use case,
+                // which is to report breaking change in drop order by Edition 2024
+                write!(fmt, "backward incompatible drop({place:?})")
+            }
         }
     }
 }