lib: init strings.join

lib/default.nix

@@ -331,6 +331,7 @@ let
         hasInfix
         hasPrefix
         hasSuffix
+        join
         stringToCharacters
         stringAsChars
         escape

lib/strings.nix

@@ -41,6 +41,36 @@ rec {
     unsafeDiscardStringContext
     ;
 
+  /**
+    Concatenates a list of strings with a separator between each element.
+
+    # Inputs
+
+    `sep`
+    : Separator to add between elements
+
+    `list`
+    : List of strings that will be joined
+
+    # Type
+
+    ```
+    join :: string -> [ string ] -> string
+    ```
+
+    # Examples
+    :::{.example}
+    ## `lib.strings.join` usage example
+
+    ```nix
+    join ", " ["foo" "bar"]
+    => "foo, bar"
+    ```
+
+    :::
+  */
+  join = builtins.concatStringsSep;
+
   /**
     Concatenate a list of strings.
 

lib/tests/misc.nix

@@ -69,6 +69,7 @@ let
     id
     ifilter0
     isStorePath
+    join
     lazyDerivation
     length
     lists
@@ -435,6 +436,15 @@ runTests {
 
   # STRINGS
 
+  testJoin = {
+    expr = join "," [
+      "a"
+      "b"
+      "c"
+    ];
+    expected = "a,b,c";
+  };
+
   testConcatMapStrings = {
     expr = concatMapStrings (x: x + ";") [
       "a"