stage2: fix Cache debug deadlock code memory leak

Author: andrewrk

src/Cache.zig

@@ -16,8 +16,8 @@ const Allocator = std.mem.Allocator;
 /// This protection is conditionally compiled depending on `want_debug_deadlock`.
 var all_cache_digest_set: std.AutoHashMapUnmanaged(BinDigest, void) = .{};
 var all_cache_digest_lock: std.Mutex = .{};
-// TODO: Figure out how to make sure that `all_cache_digest_set` does not leak memory!
-pub const want_debug_deadlock = false;
+var all_cache_digest_allocator: ?*Allocator = null;
+const want_debug_deadlock = std.debug.runtime_safety;
 const DebugBinDigest = if (want_debug_deadlock) BinDigest else void;
 const null_debug_bin_digest = if (want_debug_deadlock) ([1]u8{0} ** bin_digest_len) else {};
 
@@ -273,6 +273,14 @@ pub const Manifest = struct {
             const held = all_cache_digest_lock.acquire();
             defer held.release();
 
+            if (all_cache_digest_allocator) |prev_gpa| {
+                if (prev_gpa != self.cache.gpa) {
+                    @panic("The deadlock debug code in Cache depends on using the same allocator for everything");
+                }
+            } else {
+                all_cache_digest_allocator = self.cache.gpa;
+            }
+
             const gop = try all_cache_digest_set.getOrPut(self.cache.gpa, bin_digest);
             if (gop.found_existing) {
                 std.debug.print("Cache deadlock detected in Cache.hit. Manifest has {d} files:\n", .{self.files.items.len});
@@ -717,15 +725,22 @@ fn isProblematicTimestamp(fs_clock: i128) bool {
     return wall_nsec == fs_nsec and wall_sec == fs_sec;
 }
 
+pub fn deinitDebugMap() void {
+    if (!want_debug_deadlock) return;
+
+    if (all_cache_digest_set.count() != 0) {
+        @panic("there's a Cache not deinitialized somewhere");
+    }
+    const gpa = all_cache_digest_allocator orelse return;
+    all_cache_digest_set.clearAndFree(gpa);
+}
+
 test "cache file and then recall it" {
     if (std.Target.current.os.tag == .wasi) {
         // https://github.com/ziglang/zig/issues/5437
         return error.SkipZigTest;
     }
-    defer if (want_debug_deadlock) {
-        testing.expect(all_cache_digest_set.count() == 0);
-        all_cache_digest_set.clearAndFree(testing.allocator);
-    };
+    defer deinitDebugMap();
 
     const cwd = fs.cwd();
 
@@ -804,10 +819,7 @@ test "check that changing a file makes cache fail" {
         // https://github.com/ziglang/zig/issues/5437
         return error.SkipZigTest;
     }
-    defer if (want_debug_deadlock) {
-        testing.expect(all_cache_digest_set.count() == 0);
-        all_cache_digest_set.clearAndFree(testing.allocator);
-    };
+    defer deinitDebugMap();
     const cwd = fs.cwd();
 
     const temp_file = "cache_hash_change_file_test.txt";
@@ -884,10 +896,7 @@ test "no file inputs" {
         // https://github.com/ziglang/zig/issues/5437
         return error.SkipZigTest;
     }
-    defer if (want_debug_deadlock) {
-        testing.expect(all_cache_digest_set.count() == 0);
-        all_cache_digest_set.clearAndFree(testing.allocator);
-    };
+    defer deinitDebugMap();
     const cwd = fs.cwd();
     const temp_manifest_dir = "no_file_inputs_manifest_dir";
     defer cwd.deleteTree(temp_manifest_dir) catch {};
@@ -933,10 +942,7 @@ test "Manifest with files added after initial hash work" {
         // https://github.com/ziglang/zig/issues/5437
         return error.SkipZigTest;
     }
-    defer if (want_debug_deadlock) {
-        testing.expect(all_cache_digest_set.count() == 0);
-        all_cache_digest_set.clearAndFree(testing.allocator);
-    };
+    defer deinitDebugMap();
     const cwd = fs.cwd();
 
     const temp_file1 = "cache_hash_post_file_test1.txt";

src/main.zig

@@ -104,7 +104,10 @@ pub fn log(
 var general_purpose_allocator = std.heap.GeneralPurposeAllocator(.{}){};
 
 pub fn main() anyerror!void {
-    const gpa = if (std.builtin.link_libc) std.heap.raw_c_allocator else &general_purpose_allocator.allocator;
+    const gpa = if (std.builtin.link_libc)
+        std.heap.raw_c_allocator
+    else
+        &general_purpose_allocator.allocator;
     defer if (!std.builtin.link_libc) {
         _ = general_purpose_allocator.deinit();
     };
@@ -3289,6 +3292,7 @@ fn detectNativeTargetInfo(gpa: *Allocator, cross_target: std.zig.CrossTarget) !s
 /// calls exit(0), and does not return.
 pub fn cleanExit() void {
     if (std.builtin.mode == .Debug) {
+        Cache.deinitDebugMap();
         return;
     } else {
         process.exit(0);

src/test.zig

@@ -518,6 +518,7 @@ pub const TestContext = struct {
             case.updates.deinit();
         }
         self.cases.deinit();
+        @import("Cache.zig").deinitDebugMap();
         self.* = undefined;
     }