idris2Packages.buildIdris: better nix-shell support via shellHook

pkgs/development/compilers/idris2/build-idris.nix

@@ -32,7 +32,8 @@ let
     "idrisLibraries"
   ];
 
-  sharedAttrs = drvAttrs // {
+  derivation = stdenv.mkDerivation (finalAttrs:
+    drvAttrs // {
       pname = ipkgName;
       inherit version;
       src = src;
@@ -50,10 +51,15 @@ let
       passthru = {
         inherit propagatedIdrisLibraries;
       };
-  };
+
+      shellHook = ''
+        export IDRIS2_PACKAGE_PATH="${finalAttrs.IDRIS2_PACKAGE_PATH}"
+      '';
+    }
+  );
 
 in {
-  executable = stdenv.mkDerivation (sharedAttrs // {
+  executable = derivation.overrideAttrs {
     installPhase = ''
       runHook preInstall
       mkdir -p $out/bin
@@ -76,11 +82,11 @@ in {
       fi
       runHook postInstall
     '';
-  });
+  };
 
   library = { withSource ? false }:
     let installCmd = if withSource then "--install-with-src" else "--install";
-    in stdenv.mkDerivation (sharedAttrs // {
+    in derivation.overrideAttrs {
       installPhase = ''
         runHook preInstall
         mkdir -p $out/${libSuffix}
@@ -88,5 +94,5 @@ in {
         idris2 ${installCmd} ${ipkgFileName}
         runHook postInstall
       '';
-    });
+    };
 }