lib.strings.concatMapAttrsStringSep: init

lib/default.nix

@@ -99,7 +99,7 @@ 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 +269,37 @@ 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.
+
+    # 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 =
+    # Separator to add between items
+    sep:
+    # Function that receives the attribute name and the value
+    f:
+    # Attribute set to map from
+    attrs:
+    concatMapStringsSep sep (name: f name attrs.${name}) (lib.attrNames 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
@@ -330,6 +331,11 @@ 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";

pkgs/applications/virtualization/singularity/generic.nix

@@ -132,10 +132,6 @@ let
     lib.optional (privileged-un-utils != null) (lib.makeBinPath [ privileged-un-utils ])
     ++ args.systemBinPaths or [ "/run/wrappers/bin" ];
 
-  concatMapStringAttrsSep =
-    sep: f: attrs:
-    lib.concatMapStringsSep sep (name: f name attrs.${name}) (lib.attrNames attrs);
-
   addShellDoubleQuotes = s: lib.escapeShellArg ''"'' + s + lib.escapeShellArg ''"'';
 in
 (buildGoModule {
@@ -240,7 +236,7 @@ in
     patchShebangs --build "$configureScript" makeit e2e scripts mlocal/scripts
 
     # Patching the hard-coded defaultPath by prefixing the packages in defaultPathInputs
-    ${concatMapStringAttrsSep "\n" (fileName: originalDefaultPaths: ''
+    ${lib.concatMapAttrsStringSep "\n" (fileName: originalDefaultPaths: ''
       substituteInPlace ${lib.escapeShellArg fileName} \
         ${
           lib.concatMapStringsSep " \\\n  " (

pkgs/test/overriding.nix

@@ -58,5 +58,5 @@ stdenvNoCC.mkDerivation {
   passthru = { inherit tests; };
   buildCommand = ''
     touch $out
-  '' + lib.concatStringsSep "\n" (lib.attrValues (lib.mapAttrs (name: t: "([[ ${lib.boolToString t.expr} == ${lib.boolToString t.expected} ]] && echo '${name} success') || (echo '${name} fail' && exit 1)") tests));
+  '' + lib.concatMapAttrsStringSep "\n" (name: t: "([[ ${lib.boolToString t.expr} == ${lib.boolToString t.expected} ]] && echo '${name} success') || (echo '${name} fail' && exit 1)") tests;
 }