d/patches: Don't require lcms runtime version >= compile-time version

If no new symbols referenced by GIMP have been introduced (as is the
case when upgrading from 2.9 to 2.12~rc1), we only need a dependency
on version 2.9.

Closes: #900819
Closes: #986192

debian/patches/app-Don-t-second-guess-the-dependency-system.patch

@@ -0,0 +1,56 @@
+From: Simon McVittie <smcv@debian.org>
+Date: Sat, 3 Apr 2021 11:40:22 +0100
+Subject: app: Don't second-guess the dependency system
+
+Removing this check makes the treatment of LittleCMS consistent with
+all the other dependencies checked in the same file, which only check
+that the runtime version is at least the required version.
+
+As long as we were compiled against LittleCMS >= 2.8, and are now
+running against a version that has at least the same symbols, it doesn't
+necessarily matter whether the version we are running against is the
+same one we were compiled against.
+
+Distributions like Debian and Ubuntu track the versions in which
+individual symbols were introduced, which allows runtime dependencies
+to be weakened when no newer symbols are actually used; this is
+practically necessary when working with very large numbers of packages,
+to avoid a new version of a dependency library unnecessarily blocking
+upgrade of dependent packages. However, this doesn't work if dependent
+packages add their own checks that bypass this mechanism.
+
+Bug-Debian: https://bugs.debian.org/900819
+Bug-Debian: https://bugs.debian.org/986192
+Signed-off-by: Simon McVittie <smcv@debian.org>
+Forwarded: https://gitlab.gnome.org/GNOME/gimp/-/merge_requests/430
+---
+ app/sanity.c | 16 ----------------
+ 1 file changed, 16 deletions(-)
+
+diff --git a/app/sanity.c b/app/sanity.c
+index 7360fd0..a0550d3 100644
+--- a/app/sanity.c
++++ b/app/sanity.c
+@@ -391,22 +391,6 @@ sanity_check_lcms (void)
+ 
+   gint lcms_version = cmsGetEncodedCMMversion ();
+ 
+-  if (LCMS_VERSION > lcms_version)
+-    {
+-      return g_strdup_printf
+-        ("Liblcms2 version mismatch!\n\n"
+-         "GIMP was compiled against LittleCMS version %d.%d, but the\n"
+-         "LittleCMS version found at runtime is only %d.%d.\n\n"
+-         "Somehow you or your software packager managed\n"
+-         "to install a LittleCMS that is older than what GIMP was\n"
+-         "built against.\n\n"
+-         "Please make sure that the installed LittleCMS version\n"
+-         "is at least %d.%d and that headers and library match.",
+-         LCMS_VERSION / 1000, LCMS_VERSION % 1000 / 10,
+-         lcms_version / 1000, lcms_version % 1000 / 10,
+-         LCMS_VERSION / 1000, LCMS_VERSION % 1000 / 10);
+-    }
+-
+   if (lcms_version < (LCMS_REQUIRED_MAJOR * 1000 +
+                       LCMS_REQUIRED_MINOR * 10))
+     {

debian/patches/series

@@ -1,3 +1,4 @@
 app-Print-2-digit-LittleCMS-minor-versions-correctly.patch
+app-Don-t-second-guess-the-dependency-system.patch
 01_hurd_ftbfs.patch
 02_hurd_ftbfs.patch