From 5b7185794faf47c8907a386d60516a4fa2249e4f Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Tue, 16 Oct 2018 12:45:44 +0200
Subject: [PATCH] give machine more control over what counts as memory leak

---
 src/librustc_mir/const_eval.rs        |  8 ++++++++
 src/librustc_mir/interpret/machine.rs |  7 ++++++-
 src/librustc_mir/interpret/memory.rs  | 21 +++++++++++++--------
 src/librustc_mir/interpret/mod.rs     |  2 +-
 4 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/src/librustc_mir/const_eval.rs b/src/librustc_mir/const_eval.rs
index 497c6a2a80e..fd9af74c5d7 100644
--- a/src/librustc_mir/const_eval.rs
+++ b/src/librustc_mir/const_eval.rs
@@ -333,6 +333,14 @@ fn get_mut_or<E>(
 type CompileTimeEvalContext<'a, 'mir, 'tcx> =
     EvalContext<'a, 'mir, 'tcx, CompileTimeInterpreter<'a, 'mir, 'tcx>>;
 
+impl interpret::MayLeak for ! {
+    #[inline(always)]
+    fn may_leak(self) -> bool {
+        // `self` is uninhabited
+        self
+    }
+}
+
 impl<'a, 'mir, 'tcx> interpret::Machine<'a, 'mir, 'tcx>
     for CompileTimeInterpreter<'a, 'mir, 'tcx>
 {
diff --git a/src/librustc_mir/interpret/machine.rs b/src/librustc_mir/interpret/machine.rs
index 790a1f6b745..56909938df4 100644
--- a/src/librustc_mir/interpret/machine.rs
+++ b/src/librustc_mir/interpret/machine.rs
@@ -22,6 +22,11 @@
 
 use super::{EvalContext, PlaceTy, OpTy, MemoryKind};
 
+/// Whether this kind of memory is allowed to leak
+pub trait MayLeak: Copy {
+    fn may_leak(self) -> bool;
+}
+
 /// The functionality needed by memory to manage its allocations
 pub trait AllocMap<K: Hash + Eq, V> {
     /// Test if the map contains the given key.
@@ -63,7 +68,7 @@ fn get_mut_or<E>(
 /// and some use case dependent behaviour can instead be applied.
 pub trait Machine<'a, 'mir, 'tcx>: Sized {
     /// Additional memory kinds a machine wishes to distinguish from the builtin ones
-    type MemoryKinds: ::std::fmt::Debug + Copy + Eq + 'static;
+    type MemoryKinds: ::std::fmt::Debug + MayLeak + Eq + 'static;
 
     /// Tag tracked alongside every pointer.  This is used to implement "Stacked Borrows"
     /// <https://www.ralfj.de/blog/2018/08/07/stacked-borrows.html>.
diff --git a/src/librustc_mir/interpret/memory.rs b/src/librustc_mir/interpret/memory.rs
index d61f3e38569..51dd970e0bb 100644
--- a/src/librustc_mir/interpret/memory.rs
+++ b/src/librustc_mir/interpret/memory.rs
@@ -32,7 +32,7 @@
 
 use syntax::ast::Mutability;
 
-use super::{Machine, AllocMap, ScalarMaybeUndef};
+use super::{Machine, AllocMap, MayLeak, ScalarMaybeUndef};
 
 #[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
 pub enum MemoryKind<T> {
@@ -44,6 +44,17 @@ pub enum MemoryKind<T> {
     Machine(T),
 }
 
+impl<T: MayLeak> MayLeak for MemoryKind<T> {
+    #[inline]
+    fn may_leak(self) -> bool {
+        match self {
+            MemoryKind::Stack => false,
+            MemoryKind::Vtable => true,
+            MemoryKind::Machine(k) => k.may_leak()
+        }
+    }
+}
+
 // `Memory` has to depend on the `Machine` because some of its operations
 // (e.g. `get`) call a `Machine` hook.
 pub struct Memory<'a, 'mir, 'tcx: 'a + 'mir, M: Machine<'a, 'mir, 'tcx>> {
@@ -584,13 +595,7 @@ pub fn dump_allocs(&self, mut allocs: Vec<AllocId>) {
     pub fn leak_report(&self) -> usize {
         trace!("### LEAK REPORT ###");
         let leaks: Vec<_> = self.alloc_map.filter_map_collect(|&id, &(kind, _)| {
-            // exclude statics and vtables
-            let exclude = match kind {
-                MemoryKind::Stack => false,
-                MemoryKind::Vtable => true,
-                MemoryKind::Machine(k) => Some(k) == M::STATIC_KIND,
-            };
-            if exclude { None } else { Some(id) }
+            if kind.may_leak() { None } else { Some(id) }
         });
         let n = leaks.len();
         self.dump_allocs(leaks);
diff --git a/src/librustc_mir/interpret/mod.rs b/src/librustc_mir/interpret/mod.rs
index 39628598ef3..a174b12aaac 100644
--- a/src/librustc_mir/interpret/mod.rs
+++ b/src/librustc_mir/interpret/mod.rs
@@ -32,7 +32,7 @@
 
 pub use self::memory::{Memory, MemoryKind};
 
-pub use self::machine::{Machine, AllocMap};
+pub use self::machine::{Machine, AllocMap, MayLeak};
 
 pub use self::operand::{ScalarMaybeUndef, Value, ValTy, Operand, OpTy};