From f50c1365107c09453531f01bcaebc3b197c3627f Mon Sep 17 00:00:00 2001
From: Mark Wooding <mdw@distorted.org.uk>
Date: Thu, 26 Sep 2019 20:18:11 +0100
Subject: [PATCH] utils/macros.h: Introduce a `STATIC_ASSERT' macro.

---
 utils/macros.3 | 14 ++++++++++++++
 utils/macros.h |  9 +++++++++
 2 files changed, 23 insertions(+)

diff --git a/utils/macros.3 b/utils/macros.3
index a2a9003..98ab238 100644
--- a/utils/macros.3
+++ b/utils/macros.3
@@ -5,6 +5,7 @@ macros \- useful macros
 .\" @N
 .\" @STR
 .\" @GLUE
+.\" @STATIC_ASSERT
 .\" @DISCARD
 .\" @IGNORE
 .\" @DEPRECATED
@@ -24,6 +25,7 @@ macros \- useful macros
 .BI "size_t N(" array ");"
 .BI "STR(" tokens\fR... ")"
 .BI "GLUE(" tokens\fR... ", " tokens\fR... ")"
+.BI "STATIC_ASSERT(" cond ", " msg ");"
 
 .BI "void DISCARD(" scalar ");"
 .BI "void IGNORE(" variable ");"
@@ -64,6 +66,18 @@ and the result of gluing these tokens together must be valid
 preprocessing token.
 .PP
 The
+.B STATIC_ASSERT
+causes compilation to fail if the integer constant expression
+.I cond
+evaluates to zero.  This macro uses the C11
+.B static_assert
+declaration if available, and the
+.I msg
+will be reported in the compiler's diagnostic messsage; otherwise, the macro
+falls back to a somewhat ugly hack which currently ignores the
+.IR msg .
+.PP
+The
 .B DISCARD
 macro discards its argument, which must be of some scalar type.  This
 can be useful in muffling warnings about ignoring return codes in cases
diff --git a/utils/macros.h b/utils/macros.h
index 5f432f7..9e27a48 100644
--- a/utils/macros.h
+++ b/utils/macros.h
@@ -34,6 +34,8 @@
 
 /*----- Header files ------------------------------------------------------*/
 
+#include <assert.h>
+
 #ifndef MLIB_COMPILER_H
 #  include "compiler.h"
 #endif
@@ -48,6 +50,13 @@
 #define MLIB__GLUE(x, y) x##y
 #define GLUE(x, y) MLIB__GLUE(x, y)
 
+#ifdef static_assert
+#  define STATIC_ASSERT(cond, msg) static_assert(cond, msg)
+#else
+#  define STATIC_ASSERT(cond, msg)					\
+	IGNORABLE extern char static_assert_failed[2*!!(cond) - 1]
+#endif
+
 /*----- Compiler diagnostics ----------------------------------------------*/
 
 /* --- Compiler-specific definitions --- */
-- 
2.11.0