From 9ced3148ca18e8b057e7f2a7e773c701b95c8741 Mon Sep 17 00:00:00 2001
From: Antonio Ospite <antonio.ospite@collabora.com>
Date: Wed, 30 Jul 2025 10:33:33 +0200
Subject: [PATCH] util: avoid calling UNREACHABLE(str) macro without arguments

After commit 2dcd6bed6a9 ("util: enforce unreachable()'s argument being
a literal string", 2023-04-17) the compiler effectively emit errors when
an argument that is not a string literal is passed to UNREACHABLE(str),
however the compiler still allows the macro to be called without
arguments, which can be confusing.

Implement the type check outside of the assert() call so that we have
two types of errors:

1. The compiler will error out when the argument passed to the macro is
   not a string literal because the concatenation with an empty string
   will not be allowed.

2. The compiler will error out when no arguments are passed to the macro
   because the invocation of assert() will be invalid.

This also has the nice side-effect of removing the extra empty string
printed in the assert() messages; after the changes the messages will
look like:

  Assertion `!"Invalid type"' failed.

instead of:

  Assertion `!"" "Invalid type"' failed.

Fixes: 2dcd6bed6a9 ("util: enforce unreachable()'s argument being a literal string", 2023-04-17)

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36437>
---
 src/util/macros.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/util/macros.h b/src/util/macros.h
index af4c8c80b60..9403d337e49 100644
--- a/src/util/macros.h
+++ b/src/util/macros.h
@@ -122,17 +122,23 @@
 #if defined(HAVE___BUILTIN_UNREACHABLE) || __has_builtin(__builtin_unreachable)
 #define UNREACHABLE(str)    \
 do {                        \
-   assert(!"" str);         \
+   (void)"" str; /* str must be a string literal */ \
+   assert(!str);            \
    __builtin_unreachable(); \
 } while (0)
 #elif defined (_MSC_VER)
 #define UNREACHABLE(str)    \
 do {                        \
-   assert(!"" str);         \
+   (void)"" str; /* str must be a string literal */ \
+   assert(!str);            \
    __assume(0);             \
 } while (0)
 #else
-#define UNREACHABLE(str) assert(!"" str)
+#define UNREACHABLE(str)    \
+do {                        \
+   (void)"" str; /* str must be a string literal */ \
+   assert(!str);            \
+} while (0)
 #endif
 
 /**