Fix path add bug when given a record (#15379)

`path add`, when given a record, sets `$env.PATH` according to the value
of the key matching `$nu.os-info.name`. There already existed a check in
place to ensure the correct column existed, but it was never reached
because of an early error on `path expand`ing `null`. This has been
fixed, as well as the out-of-date reference to "darwin" instead of
"macos" in the example.

# User-Facing Changes

`path add` now simply ignores a record that doesn't include a key for the current OS

`path add` also will no longer add duplicate paths.

crates/nu-std/std/util/mod.nu

@@ -7,14 +7,14 @@
         path add "returned" --ret
     }
 } --result [returned bar baz foo fooo]
-@example "adding paths based on the operating system" {
-    path add {linux: "foo", windows: "bar", darwin: "baz"}
+@example "adding paths based on $nu.os-info.name" {
+    path add {linux: "foo", windows: "bar", macos: "baz"}
 }
 export def --env "path add" [
-    --ret (-r)  # return $env.PATH, useful in pipelines to avoid scoping.
+    --ret (-r)     # return $env.PATH, useful in pipelines to avoid scoping.
     --append (-a)  # append to $env.PATH instead of prepending to.
-    ...paths  # the paths to add to $env.PATH.
-] {
+    ...paths: any  # the paths to add to $env.PATH.
+]: [nothing -> nothing, nothing -> list<path>] {
     let span = (metadata $paths).span
     let paths = $paths | flatten
 
@@ -25,34 +25,36 @@ export def --env "path add" [
         }}
     }
 
+    for path in $paths {
+        if ($path | describe -d).type not-in ['string', 'record'] {
+            error make {msg: 'Invalid input', label: {
+                text: 'Path must be a string or record',
+                span: (metadata $path).span
+            }}
+        }
+    }
+
     let path_name = if "PATH" in $env { "PATH" } else { "Path" }
 
     let paths = $paths | each {|p|
-        let p = match ($p | describe | str replace --regex '<.*' '') {
-            "string" => $p,
-            "record" => { $p | get --ignore-errors $nu.os-info.name },
+        match ($p | describe -d).type {
+            'string' => { $p | path expand --no-symlink },
+            'record' => {
+                if $nu.os-info.name in ($p | columns) {
+                    $p | get $nu.os-info.name | path expand --no-symlink
+                }
+            }
         }
-
-        $p | path expand --no-symlink
-    }
-
-    if null in $paths or ($paths | is-empty) {
-        error make {msg: "Empty input", label: {
-            text: $"Received a record, that does not contain a ($nu.os-info.name) key",
-            span: $span
-        }}
-    }
+    } | compact
 
     load-env {$path_name: (
-        $env
-            | get $path_name
-            | split row (char esep)
-            | if $append { append $paths } else { prepend $paths }
+        $env | get $path_name
+        | split row (char esep)
+        | if $append { append $paths } else { prepend $paths }
+        | uniq
     )}
 
-    if $ret {
-        $env | get $path_name
-    }
+    if $ret { $env | get $path_name }
 }
 
 # The cute and friendly mascot of Nushell :)

crates/nu-std/tests/test_std_util.nu

@@ -39,6 +39,12 @@ def path_add [] {
         path add $target_paths
         assert equal (get_path) ([($target_paths | get $nu.os-info.name)] | path expand)
 
+        load-env {$path_name: []}
+        path add {}
+        assert equal (get_path) []
+
+        assert error {|| path add 1 }
+
         load-env {$path_name: [$"(["/foo", "/bar"] | path expand | str join (char esep))"]}
         path add "~/foo"
         assert equal (get_path) (["~/foo", "/foo", "/bar"] | path expand)

crates/nu-std/tests/test_util.nu

@@ -39,6 +39,12 @@ def path_add [] {
         path add $target_paths
         assert equal (get_path) ([($target_paths | get $nu.os-info.name)] | path expand)
 
+        load-env {$path_name: []}
+        path add {}
+        assert equal (get_path) ([])
+
+        assert error {|| path add 1 }
+
         load-env {$path_name: [$"(["/foo", "/bar"] | path expand | str join (char esep))"]}
         path add "~/foo"
         assert equal (get_path) (["~/foo", "/foo", "/bar"] | path expand)