reduce false positives of tail-expr-drop-order from consumed values

take 2

open up coroutines

tweak the wordings

the lint works up until 2021

We were missing one case, for ADTs, which was
causing `Result` to yield incorrect results.

only include field spans with significant types

deduplicate and eliminate field spans

switch to emit spans to impl Drops

Co-authored-by: Niko Matsakis <nikomat@amazon.com>

collect drops instead of taking liveness diff

apply some suggestions and add explantory notes

small fix on the cache

let the query recurse through coroutine

new suggestion format with extracted variable name

fine-tune the drop span and messages

bugfix on runtime borrows

tweak message wording

filter out ecosystem types earlier

apply suggestions

clippy

check lint level at session level

further restrict applicability of the lint

translate bid into nop for stable mir

detect cycle in type structure

compiler/rustc_middle/src/mir/syntax.rs

@@ -432,6 +432,18 @@ pub enum StatementKind<'tcx> {
 
     /// No-op. Useful for deleting instructions without affecting statement indices.
     Nop,
+
+    /// Marker statement indicating where `place` would be dropped.
+    /// This is semantically equivalent to `Nop`, so codegen and MIRI should interpret this
+    /// statement as such.
+    /// The only use case of this statement is for linting in MIR to detect temporary lifetime
+    /// changes.
+    BackwardIncompatibleDropHint {
+        /// Place to drop
+        place: Box<Place<'tcx>>,
+        /// Reason for backward incompatibility
+        reason: BackwardIncompatibleDropReason,
+    },
 }
 
 impl StatementKind<'_> {
@@ -452,6 +464,7 @@ impl StatementKind<'_> {
             StatementKind::Intrinsic(..) => "Intrinsic",
             StatementKind::ConstEvalCounter => "ConstEvalCounter",
             StatementKind::Nop => "Nop",
+            StatementKind::BackwardIncompatibleDropHint { .. } => "BackwardIncompatibleDropHint",
         }
     }
 }
@@ -897,6 +910,21 @@ pub enum TerminatorKind<'tcx> {
     },
 }
 
+#[derive(
+    Clone,
+    Debug,
+    TyEncodable,
+    TyDecodable,
+    Hash,
+    HashStable,
+    PartialEq,
+    TypeFoldable,
+    TypeVisitable
+)]
+pub enum BackwardIncompatibleDropReason {
+    Edition2024,
+}
+
 impl TerminatorKind<'_> {
     /// Returns a simple string representation of a `TerminatorKind` variant, independent of any
     /// values it might hold (e.g. `TerminatorKind::Call` always returns `"Call"`).