k2pdfopt: fix build against mupdf >= 1.25.0 (#397905)

pkgs/by-name/k2/k2pdfopt/package.nix

@@ -4,6 +4,7 @@
   runCommand,
   fetchzip,
   fetchurl,
+  fetchpatch,
   fetchFromGitHub,
   cmake,
   jbig2dec,
@@ -117,13 +118,43 @@ stdenv.mkDerivation rec {
           cp ${k2pdfopt_src}/mupdf_mod/pdf-* ./source/pdf/
         '';
       };
+      # mupdf_patch no longer applies cleanly against mupdf 1.25.0 or later, due to a conflicting
+      # hunk (mupdf_conflict) introduced in commit bd8d337939f36f55b96cb6984f5c7bbf2f488ce0 of mupdf.
+      # This merge conflict can be resolved as desired by reverting mupdf_conflict, applying mupdf_patch,
+      # and finally reapplying mupdf_conflict, with an increased fuzz factor (see mupdf_modded below).
+      # TODO: remove workaround with conflicting hunk when mupdf in k2pdfopt is updated to 1.25.0 or later
+      mupdf_conflict =
+        hash: revert:
+        fetchpatch {
+          name = "mupdf-conflicting-hunk" + (lib.optionalString revert "-reverted") + ".patch";
+          url = "https://github.com/ArtifexSoftware/mupdf/commit/bd8d337939f36f55b96cb6984f5c7bbf2f488ce0.patch";
+          inherit hash revert;
+          includes = [ "source/fitz/stext-device.c" ];
+          postFetch = ''
+            filterdiff -#6 "$out" > "$tmpfile"
+            mv "$tmpfile" "$out"
+          '';
+        };
       mupdf_modded = mupdf.overrideAttrs (
         {
           patches ? [ ],
           ...
         }:
         {
-          patches = patches ++ [ mupdf_patch ];
+          # The fuzz factor is increased to automatically resolve the merge conflict.
+          patchFlags = [
+            "-p1"
+            "-F3"
+          ];
+          # Reverting and reapplying the conflicting hunk is necessary, otherwise the result will be faulty.
+          patches = patches ++ [
+            # revert conflicting hunk
+            (mupdf_conflict "sha256-24tl9YBuZBYhb12yY3T0lKsA7NswfK0QcMYhb2IpepA=" true)
+            # apply modifications
+            mupdf_patch
+            # reapply conflicting hunk
+            (mupdf_conflict "sha256-bnBV7LyX1w/BXxBFF1bkA8x+/0I9Am33o8GiAeEKHYQ=" false)
+          ];
           # This function is missing in font.c, see font-win32.c
           postPatch = ''
             echo "void pdf_install_load_system_font_funcs(fz_context *ctx) {}" >> source/fitz/font.c