[PATCH] MNG detection fails with libjpeg-turbo

The Wanderer <[email protected]> Sun, 26 Nov 2017 15:36:34 -0500

Newsgroups	gmane.comp.video.mplayer.devel
Organization	This space intentionally left blank.
Message-ID	<[email protected]>

With current SVN (and for as long as I can remember checking), the
configure check for the availability of libmng fails. Today I finally
got around to looking into why.


The test performs a compile check against libmng.h, which includes
jpeglib.h. With libjpeg-turbo (the source of jpeglib.h in current
Debian), this test fails because FILE is undefined. This is typedef is
normally expected to come from stdio.h.

https://github.com/libjpeg-turbo/libjpeg-turbo/issues/17
indicates that this is intentional, for backwards compatibility with
libjpeg, and that "it is actually a design requirement of the libjpeg
API that you include stdio.h before including jpeglib.h.".

This would seem to indicate that this has been broken for a very long
time, and quite possibly no one noticed (which would imply that no one
bothered trying to compile with MNG support). The last MNG-related
commits seem to have been in 2012; support was originally added in 2011.


The compilation check is performed by the return_statement_check
function, which only permits passing one header-file argument. There is
an existing statement_check_broken function, specifically for use with
headers which don't include some of their own dependencies; however, it
hardcodes a 'return 0', whereas return_statement_check permits passing
in an expression to be used in the return statement.

Rather than try to add an ' 0' to all callers of statement_check_broken,
I've duplicated it into return_statement_check_broken, which adds the
return-statement argument from return_statement_check.

With that, detection of libmng succeeds. With an include of stdio.h
added to vo_mng.c, compilation also succeeds.

The attached patch makes both changes.

-- 
   The Wanderer

The reasonable man adapts himself to the world; the unreasonable one
persists in trying to adapt the world to himself. Therefore all
progress depends on the unreasonable man.         -- George Bernard Shaw

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libmng-detection-fix.diff (text/x-diff, 1.1 KB)

Index: configure
===================================================================
--- configure	(revision 38007)
+++ configure	(working copy)
@@ -177,6 +177,16 @@
   compile_check $TMPC $@
 }
 
+return_statement_check_broken() {
+  cat > $TMPC << EOF
+#include <$1>
+#include <$2>
+int main(void) { $3; return $4; }
+EOF
+  shift 4
+  compile_check $TMPC $@
+}
+
 yasm_check() {
   echo >> "$TMPLOG"
   cat "$TMPS" >> "$TMPLOG"
@@ -5303,7 +5313,7 @@
 if test "$_mng" = auto ; then
   _mng=no
   for mnglibs in '-lmng -lz' '-lmng -ljpeg -lz' ; do
-    return_statement_check libmng.h 'const char * p_ver = mng_version_text()' '!p_ver || p_ver[0] == 0' $mnglibs && _mng=yes
+    return_statement_check_broken stdio.h libmng.h 'const char * p_ver = mng_version_text()' '!p_ver || p_ver[0] == 0' $mnglibs && _mng=yes
   done
 fi
 echores "$_mng"
Index: libvo/vo_mng.c
===================================================================
--- libvo/vo_mng.c	(revision 38007)
+++ libvo/vo_mng.c	(working copy)
@@ -20,6 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>

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