From 3535c75fa87d780db2436955c5d105de3e68f125 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B8rn=20Erik=20Pedersen?=
 <bjorn.erik.pedersen@gmail.com>
Date: Wed, 5 Dec 2018 15:19:25 +0100
Subject: [PATCH] Add MergeConfigMap

Fixes #605
---
 go.mod        |  2 ++
 go.sum        |  5 +++++
 viper.go      | 12 +++++++++---
 viper_test.go | 35 +++++++++++++++++++++++++++++++++++
 4 files changed, 51 insertions(+), 3 deletions(-)

diff --git a/go.mod b/go.mod
index 3f4e1c2..ce610b3 100644
--- a/go.mod
+++ b/go.mod
@@ -6,10 +6,12 @@ require (
 	github.com/magiconair/properties v1.8.0
 	github.com/mitchellh/mapstructure v1.0.0
 	github.com/pelletier/go-toml v1.2.0
+	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/spf13/afero v1.1.2
 	github.com/spf13/cast v1.2.0
 	github.com/spf13/jwalterweatherman v1.0.0
 	github.com/spf13/pflag v1.0.2
+	github.com/stretchr/testify v1.2.2
 	golang.org/x/sys v0.0.0-20180906133057-8cf3aee42992 // indirect
 	golang.org/x/text v0.3.0 // indirect
 	gopkg.in/yaml.v2 v2.2.1
diff --git a/go.sum b/go.sum
index 3e3b874..24cf77e 100644
--- a/go.sum
+++ b/go.sum
@@ -1,3 +1,4 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/fsnotify/fsnotify v1.4.7 h1:IXs+QLmnXW2CcXuY+8Mzv/fWEsPGWxqefPtCP5CnV9I=
 github.com/fsnotify/fsnotify v1.4.7/go.mod h1:jwhsz4b93w/PPRr/qN1Yymfu8t87LnFCMoQvtojpjFo=
@@ -9,6 +10,8 @@ github.com/mitchellh/mapstructure v1.0.0 h1:vVpGvMXJPqSDh2VYHF7gsfQj8Ncx+Xw5Y1KH
 github.com/mitchellh/mapstructure v1.0.0/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
 github.com/pelletier/go-toml v1.2.0 h1:T5zMGML61Wp+FlcbWjRDT7yAxhJNAiPPLOFECq181zc=
 github.com/pelletier/go-toml v1.2.0/go.mod h1:5z9KED0ma1S8pY6P1sdut58dfprrGBbd/94hg7ilaic=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/spf13/afero v1.1.2 h1:m8/z1t7/fwjysjQRYbP0RD+bUIF/8tJwPdEZsI83ACI=
 github.com/spf13/afero v1.1.2/go.mod h1:j4pytiNVoe2o6bmDsKpLACNPDBIoEAkihy7loJ1B0CQ=
 github.com/spf13/cast v1.2.0 h1:HHl1DSRbEQN2i8tJmtS6ViPyHx35+p51amrdsiTCrkg=
@@ -17,6 +20,8 @@ github.com/spf13/jwalterweatherman v1.0.0 h1:XHEdyB+EcvlqZamSM4ZOMGlc93t6AcsBEu9
 github.com/spf13/jwalterweatherman v1.0.0/go.mod h1:cQK4TGJAtQXfYWX+Ddv3mKDzgVb68N+wFjFa4jdeBTo=
 github.com/spf13/pflag v1.0.2 h1:Fy0orTDgHdbnzHcsOgfCN4LtHf0ec3wwtiwJqwvf3Gc=
 github.com/spf13/pflag v1.0.2/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
+github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 golang.org/x/sys v0.0.0-20180906133057-8cf3aee42992 h1:BH3eQWeGbwRU2+wxxuuPOdFBmaiBH81O8BugSjHeTFg=
 golang.org/x/sys v0.0.0-20180906133057-8cf3aee42992/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/text v0.3.0 h1:g61tztE5qeGQ89tm6NTjjM9VPIm088od1l6aSorWRWg=
diff --git a/viper.go b/viper.go
index 1875627..ca1a2de 100644
--- a/viper.go
+++ b/viper.go
@@ -1259,13 +1259,19 @@ func (v *Viper) ReadConfig(in io.Reader) error {
 // MergeConfig merges a new configuration with an existing config.
 func MergeConfig(in io.Reader) error { return v.MergeConfig(in) }
 func (v *Viper) MergeConfig(in io.Reader) error {
-	if v.config == nil {
-		v.config = make(map[string]interface{})
-	}
 	cfg := make(map[string]interface{})
 	if err := v.unmarshalReader(in, cfg); err != nil {
 		return err
 	}
+	return v.MergeConfigMap(cfg)
+}
+
+// MergeConfigMap merges the configuration from the map given with an existing config.
+func MergeConfigMap(cfg map[string]interface{}) error { return v.MergeConfigMap(cfg) }
+func (v *Viper) MergeConfigMap(cfg map[string]interface{}) error {
+	if v.config == nil {
+		v.config = make(map[string]interface{})
+	}
 	mergeMaps(cfg, v.config, nil)
 	return nil
 }
diff --git a/viper_test.go b/viper_test.go
index 6097867..e4b4b83 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -1230,6 +1230,41 @@ func TestMergeConfigNoMerge(t *testing.T) {
 	}
 }
 
+func TestMergeConfigMap(t *testing.T) {
+	v := New()
+	v.SetConfigType("yml")
+	if err := v.ReadConfig(bytes.NewBuffer(yamlMergeExampleTgt)); err != nil {
+		t.Fatal(err)
+	}
+
+	assert := func(i int) {
+		large := v.GetInt("hello.lagrenum")
+		pop := v.GetInt("hello.pop")
+		if large != 765432101234567 {
+			t.Fatal("Got large num:", large)
+		}
+
+		if pop != i {
+			t.Fatal("Got pop:", pop)
+		}
+	}
+
+	assert(37890)
+
+	update := map[string]interface{}{
+		"hello": map[string]interface{}{
+			"pop": 1234,
+		},
+	}
+
+	if err := v.MergeConfigMap(update); err != nil {
+		t.Fatal(err)
+	}
+
+	assert(1234)
+
+}
+
 func TestUnmarshalingWithAliases(t *testing.T) {
 	v := New()
 	v.SetDefault("ID", 1)