assert: add `ASSERT_WITH_CLEANUP`

Now that we safely assert and return, we may need to be in a place where
we need to unlock mutexes or cleanup resources.  Provide
`ASSERT_WITH_CLEANUP` that permits for this behavior by taking a block.

src/util/assert_safe.h

@@ -24,6 +24,8 @@
 
 # define GIT_ASSERT_WITH_RETVAL(expr, fail) assert(expr)
 # define GIT_ASSERT_ARG_WITH_RETVAL(expr, fail) assert(expr)
+
+# define GIT_ASSERT_WITH_CLEANUP(expr, cleanup) assert(expr)
 #else
 
 /** Internal consistency check to stop the function. */
@@ -53,6 +55,20 @@
 		} \
 	} while(0)
 
+/**
+ * Go to to the given label on assertion failures; useful when you have
+ * taken a lock or otherwise need to release a resource.
+ */
+# define GIT_ASSERT_WITH_CLEANUP(expr, cleanup) \
+	GIT_ASSERT__WITH_CLEANUP(expr, GIT_ERROR_INTERNAL, "unrecoverable internal error", cleanup)
+
+# define GIT_ASSERT__WITH_CLEANUP(expr, code, msg, cleanup) do { \
+		if (!(expr)) { \
+			git_error_set(code, "%s: '%s'", msg, #expr); \
+			cleanup; \
+		} \
+	} while(0)
+
 #endif /* GIT_ASSERT_HARD */
 
 #endif

tests/util/assert.c

@@ -36,6 +36,21 @@ static const char *bad_returns_string(void)
 	return hello_world;
 }
 
+static int has_cleanup(void)
+{
+	int error = 42;
+
+	GIT_ASSERT_WITH_CLEANUP(1 + 1 == 3, {
+		error = 99;
+		goto foobar;
+	});
+
+	return 0;
+
+foobar:
+	return error;
+}
+
 void test_assert__argument(void)
 {
 	cl_git_fail(dummy_fn(NULL));
@@ -92,3 +107,11 @@ void test_assert__internal(void)
 	cl_assert_equal_i(GIT_ERROR_INTERNAL, git_error_last()->klass);
 	cl_assert_equal_s("unrecoverable internal error: '1 + 1 == 3'", git_error_last()->message);
 }
+
+void test_assert__with_cleanup(void)
+{
+	cl_git_fail_with(99, has_cleanup());
+	cl_assert(git_error_last());
+	cl_assert_equal_i(GIT_ERROR_INTERNAL, git_error_last()->klass);
+	cl_assert_equal_s("unrecoverable internal error: '1 + 1 == 3'", git_error_last()->message);
+}