I noticed this recently too on some boxes. Thanks for the good decription. This support for pkg-config style .pc files for our config scripts seems to be a never ending story. The alternative name for libgpg-error-config does not make it easier.

Just to clarify: I personally think it would be perfectly fine to say that AM_PATH_* is only supported when AM_PATH_GPG_ERROR is also used. Adding an invocation AM_PATH_GPG_ERROR is not a great hassle and alternatively pkg-config/pkgconf exists and works perfectly fine (and is a lot faster).

I just did not want to start checking 70-100 packages in Debian and submitting patches for the broken ones only to find out that my patches were made superfluous by an upstream change.
cu Andreas

In general, asking an application change is not good. Migrating to pkg-config should be an option (not requirement).
However, it's usually recommended to use libgpg-error when an application is used with libgcrypt/libksba/libassuan.

I'm going to apply changes of:

• Updating m4 just like in T6273 (of gpgme), so that AM_PATH_GPG_ERROR is not needed for existing applications.
• Updating documentation for use of PKG_CONFIG_MODULES.

I'll do that for libksba and libassuan, too.

The gcrypt change works for me. Thanks!

Ditto for ksba and assuan.

Minor nitpick regarding gpgme: It uses $host without AC_CANONICAL_HOST andf therefore throws a warning if used alone:

*** The config script "/usr/bin/gpgrt-config --libdir=/usr/lib/x86_64-linux-gnu gpgme" was
*** built for x86_64-pc-linux-gnu and thus may not match the
*** used host .
*** You may want to use the configure option --with-gpgme-prefix
*** to specify a matching config script or use $SYSROOT.

(The other m4 snippets have AC_REQUIRE([AC_CANONICAL_HOST]). This would work:

diff
--- a/src/gpgme.m4
+++ b/src/gpgme.m4
@@ -184,7 +184,8 @@ dnl config script does not match the host specification the script
 dnl is added to the gpg_config_script_warn variable.
 dnl
 AC_DEFUN([AM_PATH_GPGME],
-[ AC_REQUIRE([_AM_PATH_GPGME_CONFIG])dnl
+[ AC_REQUIRE([AC_CANONICAL_HOST])dnl
+  AC_REQUIRE([_AM_PATH_GPGME_CONFIG])dnl
   tmp=ifelse([$1], ,1:0.4.2,$1)

Thank you. Applied by : rM87061c0260bb: gpgme.m4: Set $host correctly always.