vscode-extensions.prince781.vala: fix vala language server path (#451273)

pkgs/applications/editors/vscode/extensions/prince781.vala/default.nix

@@ -2,6 +2,8 @@
   lib,
   vala-language-server,
   vscode-utils,
+  jq,
+  moreutils,
 }:
 
 vscode-utils.buildVscodeMarketplaceExtension {
@@ -13,9 +15,15 @@ vscode-utils.buildVscodeMarketplaceExtension {
   };
 
   nativeBuildInputs = [
-    vala-language-server
+    jq
+    moreutils
   ];
 
+  postInstall = ''
+    cd "$out/$installPrefix"
+    jq '.contributes.configuration.properties."vala.languageServerPath".default = "${lib.getExe vala-language-server}"' package.json | sponge package.json
+  '';
+
   meta = {
     changelog = "https://marketplace.visualstudio.com/items/prince781.vala/changelog";
     description = "Syntax highlighting and language support for the Vala / Genie languages";