(#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.

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

spec/unit/puppet/parser/functions/deep_merge_spec.rb

@@ -0,0 +1,77 @@
+#! /usr/bin/env ruby -S rspec
+
+require 'spec_helper'
+
+describe Puppet::Parser::Functions.function(:deep_merge) do
+  let(:scope) { PuppetlabsSpec::PuppetInternals.scope }
+
+  describe 'when calling deep_merge from puppet' do
+    it "should not compile when no arguments are passed" do
+      pending("Fails on 2.6.x, see bug #15912") if Puppet.version =~ /^2\.6\./
+      Puppet[:code] = '$x = deep_merge()'
+      expect {
+        scope.compiler.compile
+      }.to raise_error(Puppet::ParseError, /wrong number of arguments/)
+    end
+
+    it "should not compile when 1 argument is passed" do
+      pending("Fails on 2.6.x, see bug #15912") if Puppet.version =~ /^2\.6\./
+      Puppet[:code] = "$my_hash={'one' => 1}\n$x = deep_merge($my_hash)"
+      expect {
+        scope.compiler.compile
+      }.to raise_error(Puppet::ParseError, /wrong number of arguments/)
+    end
+  end
+
+  describe 'when calling deep_merge on the scope instance' do
+    it 'should require all parameters are hashes' do
+      expect { new_hash = scope.function_deep_merge([{}, '2'])}.to raise_error(Puppet::ParseError, /unexpected argument type String/)
+      expect { new_hash = scope.function_deep_merge([{}, 2])}.to raise_error(Puppet::ParseError, /unexpected argument type Fixnum/)
+    end
+
+    it 'should accept empty strings as puppet undef' do
+      expect { new_hash = scope.function_deep_merge([{}, ''])}.not_to raise_error(Puppet::ParseError, /unexpected argument type String/)
+    end
+
+    it 'should be able to deep_merge two hashes' do
+      new_hash = scope.function_deep_merge([{'one' => '1', 'two' => '1'}, {'two' => '2', 'three' => '2'}])
+      new_hash['one'].should   == '1'
+      new_hash['two'].should   == '2'
+      new_hash['three'].should == '2'
+    end
+
+    it 'should deep_merge multiple hashes' do
+      hash = scope.function_deep_merge([{'one' => 1}, {'one' => '2'}, {'one' => '3'}])
+      hash['one'].should == '3'
+    end
+
+    it 'should accept empty hashes' do
+      scope.function_deep_merge([{},{},{}]).should == {}
+    end
+
+    it 'should deep_merge subhashes' do
+      hash = scope.function_deep_merge([{'one' => 1}, {'two' => 2, 'three' => { 'four' => 4 } }])
+      hash['one'].should == 1
+      hash['two'].should == 2
+      hash['three'].should == { 'four' => 4 }
+    end
+
+    it 'should append to subhashes' do
+      hash = scope.function_deep_merge([{'one' => { 'two' => 2 } }, { 'one' => { 'three' => 3 } }])
+      hash['one'].should == { 'two' => 2, 'three' => 3 }
+    end
+
+    it 'should append to subhashes 2' do
+      hash = scope.function_deep_merge([{'one' => 1, 'two' => 2, 'three' => { 'four' => 4 } }, {'two' => 'dos', 'three' => { 'five' => 5 } }])
+      hash['one'].should == 1
+      hash['two'].should == 'dos'
+      hash['three'].should == { 'four' => 4, 'five' => 5 }
+    end
+
+    it 'should append to subhashes 3' do
+      hash = scope.function_deep_merge([{ 'key1' => { 'a' => 1, 'b' => 2 }, 'key2' => { 'c' => 3 } }, { 'key1' => { 'b' => 99 } }])
+      hash['key1'].should == { 'a' => 1, 'b' => 99 }
+      hash['key2'].should == { 'c' => 3 }
+    end
+  end
+end