Add `pkgs.lib.renderOptions`

This adds a new utility to intelligently convert Nix records to
command line options to reduce boilerplate for simple use cases and to
also reduce the likelihood of malformed command lines

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/cli.nix b/lib/cli.nix
new file mode 100644
index 00000000000..d794778b21a
--- /dev/null
+++ b/lib/cli.nix
@@ -0,0 +1,33 @@
+{ lib }:
+
+{ /* Automatically convert an attribute set to command-line options.
+
+     This helps protect against malformed command lines and also to reduce
+     boilerplate related to command-line construction for simple use cases.
+
+     Example:
+       renderOptions { foo = "A"; bar = 1; baz = null; qux = true; v = true; }
+       => " --bar '1' --foo 'A' --qux -v"
+  */
+  renderOptions =
+    options:
+      let
+        render = key: value:
+          let
+            hyphenate =
+              k: if builtins.stringLength k == 1 then "-${k}" else "--${k}";
+
+            renderOption = v: if v == null then "" else " ${hyphenate key} ${lib.escapeShellArg v}";
+
+            renderSwitch = if value then " ${hyphenate key}" else "";
+
+          in
+                 if builtins.isBool value
+            then renderSwitch
+            else if builtins.isList value
+            then lib.concatMapStrings renderOption value
+            else renderOption value;
+
+      in
+        lib.concatStrings (lib.mapAttrsToList render options);
+}