From ec4fddfada2ff6a67a0338a0898b96e2c16c3ede Mon Sep 17 00:00:00 2001
From: illarion Kovalchuk <illarion.kovalchuk@gmail.com>
Date: Wed, 23 Dec 2020 15:28:47 +0200
Subject: [PATCH 1/2] Allow merging configs with different types of leaf values

---
 viper.go      | 29 ++++++++++++++++-------------
 viper_test.go | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 13 deletions(-)

diff --git a/viper.go b/viper.go
index e5accf7ab..343253382 100644
--- a/viper.go
+++ b/viper.go
@@ -1780,17 +1780,6 @@ func mergeMaps(
 
 		svType := reflect.TypeOf(sv)
 		tvType := reflect.TypeOf(tv)
-		if tvType != nil && svType != tvType { // Allow for the target to be nil
-			v.logger.Error(
-				"svType != tvType",
-				"key", sk,
-				"st", svType,
-				"tt", tvType,
-				"sv", sv,
-				"tv", tv,
-			)
-			continue
-		}
 
 		v.logger.Trace(
 			"processing",
@@ -1804,13 +1793,27 @@ func mergeMaps(
 		switch ttv := tv.(type) {
 		case map[interface{}]interface{}:
 			v.logger.Trace("merging maps (must convert)")
-			tsv := sv.(map[interface{}]interface{})
+			tsv, ok := sv.(map[interface{}]interface{})
+			if !ok {
+				v.logger.Error(
+					"Could not cast sv to map[interface{}]interface{}; key=%s, st=%v, tt=%v, sv=%v, tv=%v",
+					sk, svType, tvType, sv, tv)
+				continue
+			}
+
 			ssv := castToMapStringInterface(tsv)
 			stv := castToMapStringInterface(ttv)
 			mergeMaps(ssv, stv, ttv)
 		case map[string]interface{}:
 			v.logger.Trace("merging maps")
-			mergeMaps(sv.(map[string]interface{}), ttv, nil)
+			tsv, ok := sv.(map[string]interface{})
+			if !ok {
+				jww.ERROR.Printf(
+					"Could not cast sv to map[string]interface{}; key=%s, st=%v, tt=%v, sv=%v, tv=%v",
+					sk, svType, tvType, sv, tv)
+				continue
+			}
+			mergeMaps(tsv, ttv, nil)
 		default:
 			v.logger.Trace("setting value")
 			tgt[tk] = sv
diff --git a/viper_test.go b/viper_test.go
index 8c864f117..f882fdc46 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -1912,6 +1912,22 @@ hello:
 fu: bar
 `)
 
+var jsonMergeExampleTgt = []byte(`
+{
+	"hello": {
+		"pop": 123456
+	}
+}
+`)
+
+var jsonMergeExampleSrc = []byte(`
+{
+	"hello": {
+		"pop": "pop str"
+	}
+}
+`)
+
 func TestMergeConfig(t *testing.T) {
 	v := New()
 	v.SetConfigType("yml")
@@ -1984,6 +2000,22 @@ func TestMergeConfig(t *testing.T) {
 	}
 }
 
+func TestMergeConfigOverrideType(t *testing.T) {
+	v := New()
+	v.SetConfigType("json")
+	if err := v.ReadConfig(bytes.NewBuffer(jsonMergeExampleTgt)); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := v.MergeConfig(bytes.NewBuffer(jsonMergeExampleSrc)); err != nil {
+		t.Fatal(err)
+	}
+
+	if pop := v.GetString("hello.pop"); pop != "pop str" {
+		t.Fatalf("pop != \"pop str\", = %s", pop)
+	}
+}
+
 func TestMergeConfigNoMerge(t *testing.T) {
 	v := New()
 	v.SetConfigType("yml")

From 02cf2b2406312c14d45061d2cb7e7c5d0ebc57e7 Mon Sep 17 00:00:00 2001
From: Illarion Kovalchuk <illarion.kovalchuk@gmail.com>
Date: Thu, 14 Oct 2021 16:29:39 +0300
Subject: [PATCH 2/2] Added test case for merging configs, where target is
 null, and source is not null

---
 viper.go      | 2 +-
 viper_test.go | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/viper.go b/viper.go
index 343253382..3481d1da1 100644
--- a/viper.go
+++ b/viper.go
@@ -1808,7 +1808,7 @@ func mergeMaps(
 			v.logger.Trace("merging maps")
 			tsv, ok := sv.(map[string]interface{})
 			if !ok {
-				jww.ERROR.Printf(
+				v.logger.Error(
 					"Could not cast sv to map[string]interface{}; key=%s, st=%v, tt=%v, sv=%v, tv=%v",
 					sk, svType, tvType, sv, tv)
 				continue
diff --git a/viper_test.go b/viper_test.go
index f882fdc46..8a5dec688 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -1915,6 +1915,7 @@ fu: bar
 var jsonMergeExampleTgt = []byte(`
 {
 	"hello": {
+		"foo": null,
 		"pop": 123456
 	}
 }
@@ -1923,6 +1924,7 @@ var jsonMergeExampleTgt = []byte(`
 var jsonMergeExampleSrc = []byte(`
 {
 	"hello": {
+		"foo": "foo str",
 		"pop": "pop str"
 	}
 }
@@ -2014,6 +2016,10 @@ func TestMergeConfigOverrideType(t *testing.T) {
 	if pop := v.GetString("hello.pop"); pop != "pop str" {
 		t.Fatalf("pop != \"pop str\", = %s", pop)
 	}
+
+	if foo := v.GetString("hello.foo"); foo != "foo str" {
+		t.Fatalf("foo != \"foo str\", = %s", foo)
+	}
 }
 
 func TestMergeConfigNoMerge(t *testing.T) {