Fix khelpcenter manpages (#389602)

pkgs/kde/gear/khelpcenter/default.nix

@@ -1,7 +1,11 @@
 {
   mkKdeDerivation,
+  replaceVars,
   qtwebengine,
   xapian,
+  man-db,
+  python3,
+  kio-extras,
 }:
 mkKdeDerivation {
   pname = "khelpcenter";
@@ -9,6 +13,13 @@ mkKdeDerivation {
   extraBuildInputs = [
     qtwebengine
     xapian
+    python3
+    kio-extras
+  ];
+  patches = [
+    (replaceVars ./use_nix_paths_for_mansearch_utilities.patch {
+      inherit man-db;
+    })
   ];
   meta.mainProgram = "khelpcenter";
 }

pkgs/kde/gear/khelpcenter/use_nix_paths_for_mansearch_utilities.patch

@@ -0,0 +1,23 @@
+diff --git a/searchhandlers/khc_mansearch.py b/searchhandlers/khc_mansearch.py
+index ce61ed9c..a8c4c653 100755
+--- a/searchhandlers/khc_mansearch.py
++++ b/searchhandlers/khc_mansearch.py
+@@ -32,15 +32,15 @@ def main():
+     # If the query is a single word, perhaps it is the literal name of the
+     # command, or a prefix, or a substring
+     if not ' ' in words:
+-        results_prefix = subprocess.run(['whatis', '-w', words + '*'], capture_output=True, text=True)
++        results_prefix = subprocess.run(['@man-db@/bin/whatis', '-w', words + '*'], capture_output=True, text=True)
+         if results_prefix.returncode == 0:
+             command_results += results_prefix.stdout
+-        results_substring = subprocess.run(['whatis', '-w', '*' + words + '*'], capture_output=True, text=True)
++        results_substring = subprocess.run(['@man-db@/bin/whatis', '-w', '*' + words + '*'], capture_output=True, text=True)
+         if results_substring.returncode == 0:
+             command_results += results_substring.stdout
+ 
+     # Build the apropos command line
+-    apropos = ['apropos', '-L', args.lang]
++    apropos = ['@man-db@/bin/apropos', '-L', args.lang]
+     if args.method == 'and':
+         apropos.append('--and')
+     apropos.extend(words.split(' '))

pkgs/kde/gear/kio-extras/add-nixos-man-db-config-path.patch

@@ -0,0 +1,13 @@
+diff --git a/man/kio_man.cpp b/man/kio_man.cpp
+index a2fb6dbf5..cb6f373bc 100644
+--- a/man/kio_man.cpp
++++ b/man/kio_man.cpp
+@@ -868,6 +868,8 @@ void MANProtocol::constructPath(QStringList &constr_path, QStringList constr_cat
+         mc.setFileName("/etc/manpath.config"); // SuSE, Debian
+     if (!mc.exists())
+         mc.setFileName("/etc/man.config"); // Mandrake
++    if (!mc.exists())
++        mc.setFileName("/run/current-system/etc/man_db.conf"); // NixOS
+ 
+     if (mc.open(QIODevice::ReadOnly)) {
+         QTextStream is(&mc);

pkgs/kde/gear/kio-extras/default.nix

@@ -19,6 +19,10 @@
 mkKdeDerivation {
   pname = "kio-extras";
 
+  patches = [
+    # An upstream merge request is pending for this https://invent.kde.org/network/kio-extras/-/merge_requests/422
+    ./add-nixos-man-db-config-path.patch
+  ];
   extraNativeBuildInputs = [
     pkg-config
     gperf