lib/strings: add concatLines

Like `unlines` from Haskell.

The aim is to replace the `concatStringsSep "\n"` pattern for generated
files, which doesn't add a final newline.

lib/default.nix

@@ -93,7 +93,7 @@ let
       subtractLists mutuallyExclusive groupBy groupBy';
     inherit (self.strings) concatStrings concatMapStrings concatImapStrings
       intersperse concatStringsSep concatMapStringsSep
-      concatImapStringsSep makeSearchPath makeSearchPathOutput
+      concatImapStringsSep concatLines makeSearchPath makeSearchPathOutput
       makeLibraryPath makeBinPath optionalString
       hasInfix hasPrefix hasSuffix stringToCharacters stringAsChars escape
       escapeShellArg escapeShellArgs isValidPosixName toShellVar toShellVars

lib/strings.nix

@@ -127,6 +127,17 @@ rec {
     # List of input strings
     list: concatStringsSep sep (lib.imap1 f list);
 
+  /* Concatenate a list of strings, adding a newline at the end of each one.
+     Defined as `concatMapStrings (s: s + "\n")`.
+
+     Type: concatLines :: [string] -> string
+
+     Example:
+       concatLines [ "foo" "bar" ]
+       => "foo\nbar\n"
+  */
+  concatLines = concatMapStrings (s: s + "\n");
+
   /* Construct a Unix-style, colon-separated search path consisting of
      the given `subDir` appended to each of the given paths.
 

lib/tests/misc.nix

@@ -153,6 +153,11 @@ runTests {
     expected = "a,b,c";
   };
 
+  testConcatLines = {
+    expr = concatLines ["a" "b" "c"];
+    expected = "a\nb\nc\n";
+  };
+
   testSplitStringsSimple = {
     expr = strings.splitString "." "a.b.c.d";
     expected = [ "a" "b" "c" "d" ];