1 files changed, 50 insertions, 0 deletions
diff --git a/lib/std/testing/leak_count_allocator.zig b/lib/std/testing/leak_count_allocator.zig
new file mode 100644
index 0000000000..65244e529b
--- /dev/null
+++ b/lib/std/testing/leak_count_allocator.zig
@@ -0,0 +1,50 @@
+const std = @import("../std.zig");
+
+/// This allocator is used in front of another allocator and counts the numbers of allocs and frees.
+/// The test runner asserts every alloc has a corresponding free at the end of each test.
+///
+/// The detection algorithm is incredibly primitive and only accounts for number of calls.
+/// This should be replaced by the general purpose debug allocator.
+pub const LeakCountAllocator = struct {
+    count: usize,
+    allocator: std.mem.Allocator,
+    internal_allocator: *std.mem.Allocator,
+
+    pub fn init(allocator: *std.mem.Allocator) LeakCountAllocator {
+        return .{
+            .count = 0,
+            .allocator = .{
+                .reallocFn = realloc,
+                .shrinkFn = shrink,
+            },
+            .internal_allocator = allocator,
+        };
+    }
+
+    fn realloc(allocator: *std.mem.Allocator, old_mem: []u8, old_align: u29, new_size: usize, new_align: u29) ![]u8 {
+        const self = @fieldParentPtr(LeakCountAllocator, "allocator", allocator);
+        var data = try self.internal_allocator.reallocFn(self.internal_allocator, old_mem, old_align, new_size, new_align);
+        if (old_mem.len == 0) {
+            self.count += 1;
+        }
+        return data;
+    }
+
+    fn shrink(allocator: *std.mem.Allocator, old_mem: []u8, old_align: u29, new_size: usize, new_align: u29) []u8 {
+        const self = @fieldParentPtr(LeakCountAllocator, "allocator", allocator);
+        if (new_size == 0) {
+            if (self.count == 0) {
+                std.debug.panic("error - too many calls to free, most likely double free", .{});
+            }
+            self.count -= 1;
+        }
+        return self.internal_allocator.shrinkFn(self.internal_allocator, old_mem, old_align, new_size, new_align);
+    }
+
+    pub fn validate(self: LeakCountAllocator) !void {
+        if (self.count > 0) {
+            std.debug.warn("error - detected leaked allocations without matching free: {}\n", .{self.count});
+            return error.Leak;
+        }
+    }
+};