Re: Proposal: Add more compile-time asserts to exposeinconsistencies.

At Thu, 19 Sep 2019 10:07:40 +0900, Michael Paquier <michael@paquier.xyz> wrote in <20190919010740.GC22307@paquier.xyz>
> On Wed, Sep 18, 2019 at 04:46:30PM +0100, Dagfinn Ilmari Mannsåker wrote:
> > Postgres doesn't seem to have it, but it would be possible to define a
> > StaticAssertDecl macro that can be used at the file level, outside any
> > function.  See for example Perl's STATIC_ASSERT_DECL:
> >
> > https://github.com/Perl/perl5/blob/v5.30.0/perl.h#L3455-L3488
>
> That sounds like a cleaner alternative.  Thanks for the pointer.

The cause for StaticAssertStmt not being usable outside of
functions is enclosing do-while, which is needed to avoid "mixed
declaration" warnings, which we are inhibiting to use as of
now. Therefore just defining another macro defined as just
_Static_assert() works fine.

I don't find an alternative way for the tool chains that don't
have static assertion feature. In the attached diff the macro is
defined as nothing. I don't find a way to warn that the assertion
is ignored.

regards.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 90ffd89339..822b9846bf 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -4601,7 +4601,6 @@ static void write_auto_conf_file(int fd, const char *filename, ConfigVariable *h
 static void replace_auto_config_value(ConfigVariable **head_p, ConfigVariable **tail_p,
                                       const char *name, const char *value);
 
-
 /*
  * Some infrastructure for checking malloc/strdup/realloc calls
  */
diff --git a/src/include/c.h b/src/include/c.h
index f461628a24..a386a81a19 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -836,11 +836,14 @@ extern void ExceptionalCondition(const char *conditionName,
 #ifdef HAVE__STATIC_ASSERT
 #define StaticAssertStmt(condition, errmessage) \
     do { _Static_assert(condition, errmessage); } while(0)
+#define StaticAssertDecl(condition, errmessage) \
+    _Static_assert(condition, errmessage)
 #define StaticAssertExpr(condition, errmessage) \
     ((void) ({ StaticAssertStmt(condition, errmessage); true; }))
 #else                            /* !HAVE__STATIC_ASSERT */
 #define StaticAssertStmt(condition, errmessage) \
     ((void) sizeof(struct { int static_assert_failure : (condition) ? 1 : -1; }))
+#define StaticAssertDecl(condition, errmessage) /* no alternatives exist */
 #define StaticAssertExpr(condition, errmessage) \
     StaticAssertStmt(condition, errmessage)
 #endif                            /* HAVE__STATIC_ASSERT */
@@ -848,11 +851,14 @@ extern void ExceptionalCondition(const char *conditionName,
 #if defined(__cpp_static_assert) && __cpp_static_assert >= 200410
 #define StaticAssertStmt(condition, errmessage) \
     static_assert(condition, errmessage)
+#define StaticAssertDecl(condition, errmessage) \
+    static_assert(condition, errmessage)
 #define StaticAssertExpr(condition, errmessage) \
     ({ static_assert(condition, errmessage); })
 #else
 #define StaticAssertStmt(condition, errmessage) \
     do { struct static_assert_struct { int static_assert_failure : (condition) ? 1 : -1; }; } while(0)
+#define StaticAssertDecl(condition, errmessage) /* no alternatives exist */
 #define StaticAssertExpr(condition, errmessage) \
     ((void) ({ StaticAssertStmt(condition, errmessage); }))
 #endif