From 5cbc6ca9bb63f939dab2c2c82a63d72f1f30d9b7 Mon Sep 17 00:00:00 2001
From: Profpatsch <mail@profpatsch.de>
Date: Mon, 12 Jun 2017 07:07:59 +0200
Subject: lib/generators: put more information in toPretty lambdas

With `builtins.functionArgs` we can get some information if the first argument
is an attrset and whether the contained fields have default values. Encode that
into the pretty-printed lambda.
---
 lib/generators.nix | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

(limited to 'lib/generators.nix')

diff --git a/lib/generators.nix b/lib/generators.nix
index 0e5ce864356a..4419c3c88917 100644
--- a/lib/generators.nix
+++ b/lib/generators.nix
@@ -91,7 +91,6 @@ rec {
     */
   toYAML = {}@args: toJSON args;
 
-  # TODO we need some kind of pattern matching sometimes
   /* Pretty print a value, akin to `builtins.trace`.
     * Should probably be a builtin as well.
     */
@@ -105,7 +104,13 @@ rec {
     else if isBool     v then (if v == true then "true" else "false")
     else if isString   v then "\"" + v + "\""
     else if null ==    v then "null"
-    else if isFunction v then "<λ>"
+    else if isFunction v then
+      let fna = functionArgs v;
+          showFnas = concatStringsSep "," (libAttr.mapAttrsToList
+                       (name: hasDefVal: if hasDefVal then "(${name})" else name)
+                       fna);
+      in if fna == {}    then "<λ>"
+                         else "<λ:{${showFnas}}>"
     else if isList     v then "[ "
         + libStr.concatMapStringsSep " " (toPretty args) v
       + " ]"
-- 
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