Recently I found that GIMP from git would not compile, as it couldn't get past the ./autogen.sh step..
It would produce quite a few errors, like this:

gtk-doc.make:53: GTK_DOC_BUILD_HTML does not appear in AM_CONDITIONAL devel-docs/app/Makefile.am:116: `gtk-doc.make' included from here gtk-doc.make:58: GTK_DOC_BUILD_PDF does not appear in AM_CONDITIONAL devel-docs/app/Makefile.am:116: `gtk-doc.make' included from here gtk-doc.make:53: GTK_DOC_BUILD_HTML does not appear in AM_CONDITIONAL devel-docs/libgimp/Makefile.am:64: `gtk-doc.make' included from here gtk-doc.make:58: GTK_DOC_BUILD_PDF does not appear in AM_CONDITIONAL devel-docs/libgimp/Makefile.am:64: `gtk-doc.make' included from here gtk-doc.make:53: GTK_DOC_BUILD_HTML does not appear in AM_CONDITIONAL devel-docs/libgimpbase/Makefile.am:52: `gtk-doc.make' included from here gtk-doc.make:58: GTK_DOC_BUILD_PDF does not appear in AM_CONDITIONAL devel-docs/libgimpbase/Makefile.am:52: `gtk-doc.make' included from here gtk-doc.make:53: GTK_DOC_BUILD_HTML does not appear in AM_CONDITIONAL devel-docs/libgimpcolor/Makefile.am:46: `gtk-doc.make' included from here

I noticed in my pacman logs, I had upgraded gtk-doc recently:

"[2009-12-21 10:55] upgraded gtk-doc (1.11-2 -> 1.13-1)"

So I eventually decided these BUILD_PDF and BUILD_HTML flags were new in 1.13 (or 1.12 if it exists) and required in configure.ac, and I hacked around this, by adding

AM_CONDITIONAL(GTK_DOC_BUILD_HTML, test "x$jpeg_ok" = xyes) AM_CONDITIONAL(GTK_DOC_BUILD_PDF, test "x$jpeg_ok" = xyes)

after

AM_CONDITIONAL(BUILD_JPEG, test "x$jpeg_ok" = xyes) AC_SUBST(JPEG_LIBS)

to configure.ac

Of course, that is somewhat nonsensical.. perhaps 'true = xyes' would work instead of 'test "x$jpeg_ok" = xyes'. The above fix allowed me to build GIMP successfully (actually is in progress now, so I'll check it actually finishes OK.. yep:)

It does seem odd to me that I get the above errors even if building devel docs with gtk-doc is disabled... Is that a bug in configure.ac?