direnv: Apply nushell env transformations

In nushell, the ENV_CONVERSIONS environment variable is used to
transform the defined variables from a string to a nushell value (PATH
to a list being one of the most common uses). This commit applies
user-defined conversions to direnv-loaded variables.

This fixes binary autocompletion not being triggered for newly added
paths and makes direnv work consistently with nushell

modules/programs/direnv.nix

@@ -132,16 +132,21 @@ in {
       # Using mkAfter to make it more likely to appear after other
       # manipulations of the prompt.
       mkAfter ''
-        $env.config = ($env | default {} config).config
-        $env.config = ($env.config | default {} hooks)
-        $env.config = ($env.config | update hooks ($env.config.hooks | default [] pre_prompt))
-        $env.config = ($env.config | update hooks.pre_prompt ($env.config.hooks.pre_prompt | append {
-          code: "
-            let direnv = (${cfg.package}/bin/direnv export json | from json)
-            let direnv = if not ($direnv | is-empty) { $direnv } else { {} }
-            $direnv | load-env
-            "
-        }))
+        $env.config = ($env.config? | default {})
+        $env.config.hooks = ($env.config.hooks? | default {})
+        $env.config.hooks.pre_prompt = ($env.config.hooks.pre_prompt? | default [] | append {||
+            let direnv = (${cfg.package}/bin/direnv export json | from json | default {})
+            if ($direnv | is-empty) {
+                return
+            }
+            $direnv
+            | items {|key, value|
+                {
+                    key: $key
+                    value: (do ($env.ENV_CONVERSIONS? | default {} | get -i $key | get -i from_string | default {|x| $x}) $value)
+                }
+            } | transpose -ird | load-env
+        })
       '');
   };
 }

tests/modules/programs/direnv/nushell.nix

@@ -14,6 +14,6 @@
   in ''
     assertFileExists "${configFile}"
     assertFileRegex "${configFile}" \
-      'let direnv = (/nix/store/.*direnv.*/bin/direnv export json | from json)'
+      'let direnv = (/nix/store/.*direnv.*/bin/direnv export json \| from json | default {})'
   '';
 }