From 682f89d5bc1fbc28260ccf98f4ebc7798a5cd46c Mon Sep 17 00:00:00 2001
From: Michel Hermier <michel.hermier@gmail.com>
Date: Tue, 14 Dec 2021 17:44:43 +0100
Subject: [PATCH] LibC: Allow multiple includes of `<assert.h>`

ISO C requires in section 7.2:
The assert macro is redefined according to the current state of NDEBUG
each time that <assert.h> is included.

Also add tests for `assert` multiple inclusion accordingly.
---
 Meta/check-style.py              |  1 +
 Tests/LibC/TestAssert.cpp        | 23 +++++++++++++++++++++++
 Userland/Libraries/LibC/assert.h | 19 ++++++++++++-------
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/Meta/check-style.py b/Meta/check-style.py
index 24ea096b94..5e70d79ef9 100755
--- a/Meta/check-style.py
+++ b/Meta/check-style.py
@@ -31,6 +31,7 @@ LICENSE_HEADER_CHECK_EXCLUDES = {
 # We check that "#pragma once" is present
 PRAGMA_ONCE_STRING = '#pragma once'
 PRAGMA_ONCE_CHECK_EXCLUDES = {
+    'Userland/Libraries/LibC/assert.h',
 }
 
 # We make sure that there's a blank line before and after pragma once
diff --git a/Tests/LibC/TestAssert.cpp b/Tests/LibC/TestAssert.cpp
index 08eae12c23..2e7b5fb706 100644
--- a/Tests/LibC/TestAssert.cpp
+++ b/Tests/LibC/TestAssert.cpp
@@ -6,6 +6,7 @@
 
 #include <LibTest/TestCase.h>
 
+#undef NDEBUG
 #include <assert.h>
 #include <signal.h>
 
@@ -20,3 +21,25 @@ TEST_CASE(assert)
         return Test::Crash::Failure::DidNotCrash;
     });
 }
+
+#define NDEBUG
+#include <assert.h>
+
+TEST_CASE(assert_reinclude)
+{
+    EXPECT_NO_CRASH("This should not assert", [] {
+        assert(!"This should not assert");
+        return Test::Crash::Failure::DidNotCrash;
+    });
+}
+
+#undef NDEBUG
+#include <assert.h>
+
+TEST_CASE(assert_rereinclude)
+{
+    EXPECT_CRASH("This should assert", [] {
+        assert(!"This should assert");
+        return Test::Crash::Failure::DidNotCrash;
+    });
+}
diff --git a/Userland/Libraries/LibC/assert.h b/Userland/Libraries/LibC/assert.h
index 86c042281c..c64b51ecd0 100644
--- a/Userland/Libraries/LibC/assert.h
+++ b/Userland/Libraries/LibC/assert.h
@@ -4,16 +4,25 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
-#pragma once
+#ifndef _ASSERT_H
+#    define _ASSERT_H
+
+#    define __stringify_helper(x) #    x
+#    define __stringify(x) __stringify_helper(x)
+
+#    ifndef __cplusplus
+#        define static_assert _Static_assert
+#    endif
+#endif
 
 #include <sys/cdefs.h>
 
+#undef assert
+
 __BEGIN_DECLS
 
 #ifndef NDEBUG
 __attribute__((noreturn)) void __assertion_failed(const char* msg);
-#    define __stringify_helper(x) #    x
-#    define __stringify(x) __stringify_helper(x)
 #    define assert(expr)                                                            \
         (__builtin_expect(!(expr), 0)                                               \
                 ? __assertion_failed(#expr "\n" __FILE__ ":" __stringify(__LINE__)) \
@@ -23,8 +32,4 @@ __attribute__((noreturn)) void __assertion_failed(const char* msg);
 #    define assert(expr) ((void)(0))
 #endif
 
-#ifndef __cplusplus
-#    define static_assert _Static_assert
-#endif
-
 __END_DECLS