nexusmods-app: fix desktop entry (#421259)

pkgs/by-name/ne/nexusmods-app/package.nix

···
   _7zz,
   avalonia,
   buildDotnetModule,
-  copyDesktopItems,
   desktop-file-utils,
   dotnetCorePackages,
   fetchgit,
···
   nativeCheckInputs = [ _7zz ];
 
   nativeBuildInputs = [
-    copyDesktopItems
     imagemagick # For resizing SVG icon in postInstall
   ];
 
···
   ];
 
   postInstall = ''
+    ${lib.strings.toShellVars {
+      inherit (finalAttrs.meta) mainProgram;
+      INSTALL_EXEC = "\${INSTALL_EXEC}";
+      INSTALL_TRYEXEC = "\${INSTALL_TRYEXEC}";
+    }}
+
     # Desktop entry
     # As per #308324, use mainProgram from PATH, instead of $out/bin/NexusMods.App
     install -D -m 444 -t $out/share/applications src/NexusMods.App/com.nexusmods.app.desktop
     substituteInPlace $out/share/applications/com.nexusmods.app.desktop \
-      --replace-fail '${"$"}{INSTALL_EXEC}' "${finalAttrs.meta.mainProgram}"
+      --replace-fail "$INSTALL_EXEC" "$mainProgram" \
+      --replace-fail "$INSTALL_TRYEXEC" "$mainProgram"
 
     # AppStream metadata
     install -D -m 444 -t $out/share/metainfo src/NexusMods.App/com.nexusmods.app.metainfo.xml
···
     ++ lib.optionals (!_7zz.meta.unfree) [
       "NexusMods.Games.FOMOD.Tests.FomodXmlInstallerTests.InstallsFilesSimple_UsingRar"
     ];
+
+  doInstallCheck = true;
+
+  nativeInstallCheckInputs = [
+    desktop-file-utils
+  ];
+
+  # Upstream use ${...} templates in the desktop entry, so assert that we haven't missed any
+  # See https://github.com/NixOS/nixpkgs/issues/421241
+  installCheckPhase = ''
+    runHook preInstallCheck
+
+    echo 'Checking for issues in $out/share/applications/com.nexusmods.app.desktop'
+    (
+      cd $out/share/applications
+      desktop-file-validate com.nexusmods.app.desktop
+      if grep '\$' com.nexusmods.app.desktop \
+        --with-filename --line-number
+      then
+        echo 'error: unexpected "$"'
+        exit 1
+      fi
+    ) &>/dev/stderr
+
+    runHook postInstallCheck
+  '';
 
   passthru.updateScript = nix-update-script { };