(#20200) Add a recursive merge function.

Issue #20200 notes that the merge function does not
support nested hashes.

To prevent unintended side effects with changing merge,
add a deep_merge function instead.

1 files changed, 44 insertions, 0 deletions

diff --git a/lib/puppet/parser/functions/deep_merge.rb b/lib/puppet/parser/functions/deep_merge.rb
new file mode 100644
index 0000000..94677b8
--- /dev/null
+++ b/lib/puppet/parser/functions/deep_merge.rb
@@ -0,0 +1,44 @@
+module Puppet::Parser::Functions
+  newfunction(:deep_merge, :type => :rvalue, :doc => <<-'ENDHEREDOC') do |args|
+    Recursively merges two or more hashes together and returns the resulting hash.
+
+    For example:
+
+        $hash1 = {'one' => 1, 'two' => 2, 'three' => { 'four' => 4 } }
+        $hash2 = {'two' => 'dos', 'three' => { 'five' => 5 } }
+        $merged_hash = deep_merge($hash1, $hash2)
+        # The resulting hash is equivalent to:
+        # $merged_hash = { 'one' => 1, 'two' => 'dos', 'three' => { 'four' => 4, 'five' => 5 } }
+
+    When there is a duplicate key that is a hash, they are recursively merged.
+    When there is a duplicate key that is not a hash, the key in the rightmost hash will "win."
+
+    ENDHEREDOC
+
+    if args.length < 2
+      raise Puppet::ParseError, ("deep_merge(): wrong number of arguments (#{args.length}; must be at least 2)")
+    end
+
+    deep_merge = Proc.new do |hash1,hash2|
+      hash1.merge!(hash2) do |key,old_value,new_value|
+        if old_value.is_a?(Hash) && new_value.is_a?(Hash)
+          deep_merge.call(old_value, new_value)
+        else
+          new_value
+        end
+      end
+    end
+
+    result = Hash.new
+    args.each do |arg|
+      next if arg.is_a? String and arg.empty? # empty string is synonym for puppet's undef
+      # If the argument was not a hash, skip it.
+      unless arg.is_a?(Hash)
+        raise Puppet::ParseError, "deep_merge: unexpected argument type #{arg.class}, only expects hash arguments"
+      end
+
+      deep_merge.call(result, arg)
+    end
+    return( result )
+  end
+end