Rollup merge of #131593 - RalfJung:alloc-no-clone, r=saethlin

miri: avoid cloning AllocExtra

We shouldn't be cloning Miri allocations, so make `AllocExtra::clone` panic instead, and adjust the one case where we *do* clone (the leak check) to avoid cloning.

This is in preparation for rust-lang#3966 where I am adding something to `AllocExtra` that cannot (easily) be cloned.

r? ``@saethlin``

Author: matthiaskrgr

src/diagnostics.rs

@@ -473,14 +473,14 @@ pub fn report_leaks<'tcx>(
     leaks: Vec<(AllocId, MemoryKind, Allocation<Provenance, AllocExtra<'tcx>, MiriAllocBytes>)>,
 ) {
     let mut any_pruned = false;
-    for (id, kind, mut alloc) in leaks {
+    for (id, kind, alloc) in leaks {
         let mut title = format!(
             "memory leaked: {id:?} ({}, size: {:?}, align: {:?})",
             kind,
             alloc.size().bytes(),
             alloc.align.bytes()
         );
-        let Some(backtrace) = alloc.extra.backtrace.take() else {
+        let Some(backtrace) = alloc.extra.backtrace else {
             ecx.tcx.dcx().err(title);
             continue;
         };

src/eval.rs

@@ -476,7 +476,7 @@ pub fn eval_entry<'tcx>(
         }
         // Check for memory leaks.
         info!("Additional static roots: {:?}", ecx.machine.static_roots);
-        let leaks = ecx.find_leaked_allocations(&ecx.machine.static_roots);
+        let leaks = ecx.take_leaked_allocations(|ecx| &ecx.machine.static_roots);
         if !leaks.is_empty() {
             report_leaks(&ecx, leaks);
             tcx.dcx().note("set `MIRIFLAGS=-Zmiri-ignore-leaks` to disable this check");

src/machine.rs

@@ -321,7 +321,7 @@ impl ProvenanceExtra {
 }
 
 /// Extra per-allocation data
-#[derive(Debug, Clone)]
+#[derive(Debug)]
 pub struct AllocExtra<'tcx> {
     /// Global state of the borrow tracker, if enabled.
     pub borrow_tracker: Option<borrow_tracker::AllocState>,
@@ -338,6 +338,14 @@ pub struct AllocExtra<'tcx> {
     pub backtrace: Option<Vec<FrameInfo<'tcx>>>,
 }
 
+// We need a `Clone` impl because the machine passes `Allocation` through `Cow`...
+// but that should never end up actually cloning our `AllocExtra`.
+impl<'tcx> Clone for AllocExtra<'tcx> {
+    fn clone(&self) -> Self {
+        panic!("our allocations should never be cloned");
+    }
+}
+
 impl VisitProvenance for AllocExtra<'_> {
     fn visit_provenance(&self, visit: &mut VisitWith<'_>) {
         let AllocExtra { borrow_tracker, data_race, weak_memory, backtrace: _ } = self;