lib.strings.concatMapAttrsStringSep: init

lib/default.nix

@@ -100,7 +100,7 @@ let
       length head tail elem elemAt isList;
     inherit (self.strings) concatStrings concatMapStrings concatImapStrings
       stringLength substring isString replaceStrings
-      intersperse concatStringsSep concatMapStringsSep
+      intersperse concatStringsSep concatMapStringsSep concatMapAttrsStringSep
       concatImapStringsSep concatLines makeSearchPath makeSearchPathOutput
       makeLibraryPath makeIncludePath makeBinPath optionalString
       hasInfix hasPrefix hasSuffix stringToCharacters stringAsChars escape

lib/strings.nix

@@ -269,6 +269,43 @@ rec {
     f:
     list: concatStringsSep sep (lib.imap1 f list);
 
+  /**
+    Like [`concatMapStringsSep`](#function-library-lib.strings.concatMapStringsSep)
+    but takes an attribute set instead of a list.
+
+    # Inputs
+
+    `sep`
+    : Separator to add between item strings
+
+    `f`
+    : Function that takes each key and value and return a string
+
+    `attrs`
+    : Attribute set to map from
+
+    # Type
+
+    ```
+    concatMapAttrsStringSep :: String -> (String -> Any -> String) -> AttrSet -> String
+    ```
+
+    # Examples
+
+    :::{.example}
+    ## `lib.strings.concatMapAttrsStringSep` usage example
+
+    ```nix
+    concatMapAttrsStringSep "\n" (name: value: "${name}: foo-${value}") { a = "0.1.0"; b = "0.2.0"; }
+    => "a: foo-0.1.0\nb: foo-0.2.0"
+    ```
+
+    :::
+  */
+  concatMapAttrsStringSep =
+    sep: f: attrs:
+    concatStringsSep sep (lib.attrValues (lib.mapAttrs f attrs));
+
   /**
     Concatenate a list of strings, adding a newline at the end of each one.
     Defined as `concatMapStrings (s: s + "\n")`.

lib/tests/misc.nix

@@ -39,6 +39,7 @@ let
     composeManyExtensions
     concatLines
     concatMapAttrs
+    concatMapAttrsStringSep
     concatMapStrings
     concatStrings
     concatStringsSep
@@ -328,6 +329,11 @@ runTests {
     expected = "a,b,c";
   };
 
+  testConcatMapAttrsStringSepExamples = {
+    expr = concatMapAttrsStringSep "\n" (name: value: "${name}: foo-${value}") { a = "0.1.0"; b = "0.2.0"; };
+    expected = "a: foo-0.1.0\nb: foo-0.2.0";
+  };
+
   testConcatLines = {
     expr = concatLines ["a" "b" "c"];
     expected = "a\nb\nc\n";