shell.nix: Pin R to prevent API breakage

shell.nix

@@ -1,43 +1,71 @@
-{ pkgs ? import ./nixpkgs.nix { }, ghc ? pkgs.haskell.compiler.ghc8107 }:
-
-with pkgs;
-
+{
+  pkgs ? import ./nixpkgs.nix {},
+  ghc ? pkgs.haskell.compiler.ghc8107,
+}:
 let
-  # Uncomment the line below to build HaskellR against a version of R with
+  callPackage = pkgs.lib.flip pkgs.callPackage {inherit R;};
+  # Set enableStrictBarrier to true to build HaskellR against a version of R with
   # the --enable-strict-barrier configure flag enabled for better memory
   # diagnostics.
+  R = (pkgs.R.override {enableStrictBarrier = false;}).overrideAttrs (
+    # Pin R to a specific version to avoid breaking changes in the R API.
+    finalAttrs: prevAttrs: {
+      version = "4.2.3";
+      src = pkgs.fetchurl {
+        url = "https://cran.r-project.org/src/base/R-${pkgs.lib.versions.major finalAttrs.version}/R-${finalAttrs.version}.tar.gz";
+        sha256 = "sha256-VeSpptQ74xTiwD0CZqb6VESv3OULMDv8O4Kzl5UW4HQ=";
+      };
+    }
+  );
+in
+callPackage (
+  {
+    fetchurl,
+    haskell,
+    lib,
+    python3,
+    rPackages,
+    rWrapper,
+    stdenv,
+    zeromq,
+    R,
+    zlib,
+  }:
+  let
+    # NOTE: Workaround https://ghc.haskell.org/trac/ghc/ticket/11042.
+    libHack =
+      if stdenv.isDarwin then
+        {DYLD_LIBRARY_PATH = ["${R}/lib/R/lib"];}
+      else
+        {LD_LIBRARY_PATH = ["${R}/lib/R"];};
 
-  # R = pkgs.R.override { enableStrictBarrier = true; };
-
-  # XXX Workaround https://ghc.haskell.org/trac/ghc/ticket/11042.
-  libHack =
-    if stdenv.isDarwin
-    then { DYLD_LIBRARY_PATH = [ "${R}/lib/R/lib" ]; }
-    else { LD_LIBRARY_PATH = [ "${R}/lib/R" ]; }
-  ;
-
-  python3Env = python3.withPackages (ps: with ps; [
-    ipython
-    jupyter_client
-    notebook
-  ]);
+    python3Env = python3.withPackages (
+      ps:
+      with ps; [
+        ipython
+        jupyter_client
+        notebook
+      ]
+    );
 
-  rEnv = rWrapper.override {
-    packages = with rPackages; [
+    rEnv = rWrapper.override {
+      inherit R;
       # ggplot2 is required for ./IHaskell/examples/tutorial-ihaskell-inline-r.ipynb
-      ggplot2
-    ];
-  };
-in
-
-haskell.lib.buildStackProject ({
-  name = "HaskellR";
-  inherit ghc;
-  buildInputs = [
-    zeromq
-    zlib
-    python3Env
-    rEnv
-  ];
-  LANG = "en_US.UTF-8";
-} // libHack)
+      packages = with rPackages; [ggplot2];
+    };
+  in
+  haskell.lib.buildStackProject (
+    {
+      name = "HaskellR";
+      inherit ghc;
+      buildInputs = [
+        zeromq
+        zlib
+        python3Env
+        rEnv
+      ];
+      LANG = "en_US.UTF-8";
+    }
+    // libHack
+  )
+)