ark: add a Jupyter kernel definition

pkgs/applications/editors/jupyter-kernels/r-ark/default.nix

@@ -0,0 +1,31 @@
+{ ark }:
+
+# Jupyter notebook:
+# nix shell --impure --expr 'with import ./. {}; [ (jupyter.override { definitions.r = r-ark-kernel.definition; }) ]' -c jupyter-notebook
+
+{
+  definition = {
+    displayName = "Ark R Kernel";
+    argv = [
+      "${ark}/bin/ark"
+      "--connection_file"
+      "{connection_file}"
+      "--session-mode"
+      "notebook"
+    ];
+    language = "R";
+    # Ark logs at INFO to stderr by default, which includes Jupyter messages.
+    # The notebook forwards this to the cell output, so quiet it to warnings.
+    #
+    # The `ark::console::console_comm=error` directive additionally silences a
+    # per-cell "UI comm is absent during dispatch" warning: after every execute,
+    # ark unconditionally tries to push an environment-pane update over the
+    # Positron-only `positron.ui` comm, which a plain Jupyter frontend never
+    # opens.
+    env = {
+      RUST_LOG = "ark=warn,ark::console::console_comm=error";
+    };
+    logo32 = null;
+    logo64 = null;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -2327,6 +2327,7 @@ with pkgs;
     definitions = {
       clojure = clojupyter.definition;
       octave = octave-kernel.definition;
+      r = r-ark-kernel.definition;
       # wolfram = wolfram-for-jupyter-kernel.definition; # unfree
     };
   };
@@ -4557,6 +4558,8 @@ with pkgs;
 
   octave-kernel = recurseIntoAttrs (callPackage ../applications/editors/jupyter-kernels/octave { });
 
+  r-ark-kernel = callPackage ../applications/editors/jupyter-kernels/r-ark { };
+
   octavePackages = recurseIntoAttrs octave.pkgs;
 
   # PHP interpreters, packages and extensions.