From 13c5586d7fec4eaf0394ec4d396a1cb773183bd3 Mon Sep 17 00:00:00 2001
From: Yueh-Shun Li <shamrocklee@posteo.net>
Date: Fri, 26 Jul 2024 03:00:09 +0800
Subject: [PATCH] lib.strings.concatMapAttrsStringSep: init

Co-authored-by: Silvan Mosberger <github@infinisil.com>
---
 lib/default.nix    |  2 +-
 lib/strings.nix    | 31 +++++++++++++++++++++++++++++++
 lib/tests/misc.nix |  6 ++++++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/lib/default.nix b/lib/default.nix
index 63a31101eee7f..2a5b11e8b6155 100644
--- a/lib/default.nix
+++ b/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
diff --git a/lib/strings.nix b/lib/strings.nix
index aafbdffaa7bc0..a6a1cafe856c1 100644
--- a/lib/strings.nix
+++ b/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")`.
diff --git a/lib/tests/misc.nix b/lib/tests/misc.nix
index d59f5586b82d7..b170b638b6a83 100644
--- a/lib/tests/misc.nix
+++ b/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";