Changes maps to merge vs. overwrite when processing configs.

Fixes #3716

agent/config/builder.go

@@ -40,7 +40,8 @@ import (
 //
 // The config sources are merged sequentially and later values
 // overwrite previously set values. Slice values are merged by
-// concatenating the two slices.
+// concatenating the two slices. Map values are merged by over-
+// laying the later maps on top of earlier ones.
 //
 // Then call Validate() to perform the semantic validation to ensure
 // that the configuration is ready to be used.

agent/config/merge.go

@@ -11,7 +11,7 @@ import (
 // * only values of type struct, slice, map and pointer to simple types are allowed. Other types panic.
 // * when merging two structs the result is the recursive merge of all fields according to the rules below
 // * when merging two slices the result is the second slice appended to the first
-// * when merging two maps the result is the second map if it is not empty, otherwise the first
+// * when merging two maps the result is the second map overlaid on the first
 // * when merging two pointer values the result is the second value if it is not nil, otherwise the first
 func Merge(files ...Config) Config {
 	var a Config
@@ -28,10 +28,16 @@ func merge(a, b interface{}) interface{} {
 func mergeValue(a, b reflect.Value) reflect.Value {
 	switch a.Kind() {
 	case reflect.Map:
-		if b.Len() > 0 {
-			return b
+		r := reflect.MakeMap(a.Type())
+		for _, k := range a.MapKeys() {
+			v := a.MapIndex(k)
+			r.SetMapIndex(k, v)
 		}
-		return a
+		for _, k := range b.MapKeys() {
+			v := b.MapIndex(k)
+			r.SetMapIndex(k, v)
+		}
+		return r
 
 	case reflect.Ptr:
 		if !b.IsNil() {

agent/config/merge_test.go

@@ -26,6 +26,7 @@ func TestMerge(t *testing.T) {
 				{StartJoinAddrsLAN: []string{"b"}},
 				{NodeMeta: map[string]string{"a": "b"}},
 				{NodeMeta: map[string]string{"c": "d"}},
+				{NodeMeta: map[string]string{"c": "e"}},
 				{Ports: Ports{DNS: pInt(1)}},
 				{Ports: Ports{DNS: pInt(2), HTTP: pInt(3)}},
 			},
@@ -34,8 +35,11 @@ func TestMerge(t *testing.T) {
 				RaftProtocol:      pInt(2),
 				ServerMode:        pBool(true),
 				StartJoinAddrsLAN: []string{"a", "b"},
-				NodeMeta:          map[string]string{"c": "d"},
-				Ports:             Ports{DNS: pInt(2), HTTP: pInt(3)},
+				NodeMeta: map[string]string{
+					"a": "b",
+					"c": "e",
+				},
+				Ports: Ports{DNS: pInt(2), HTTP: pInt(3)},
 			},
 		},
 	}

agent/config/runtime_test.go

@@ -1115,7 +1115,7 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
 						"bootstrap_expect": 0,
 						"datacenter":"b",
 						"start_join": ["c", "d"],
-						"node_meta": {"c":"d"}
+						"node_meta": {"a":"c"}
 					}`,
 			},
 			hcl: []string{
@@ -1131,7 +1131,7 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
 					bootstrap_expect = 0
 					datacenter = "b"
 					start_join = ["c", "d"]
-					node_meta = { "c" = "d" }
+					node_meta = { "a" = "c" }
 					`,
 			},
 			patch: func(rt *RuntimeConfig) {
@@ -1139,7 +1139,7 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
 				rt.BootstrapExpect = 0
 				rt.Datacenter = "b"
 				rt.StartJoinAddrsLAN = []string{"a", "b", "c", "d"}
-				rt.NodeMeta = map[string]string{"c": "d"}
+				rt.NodeMeta = map[string]string{"a": "c"}
 				rt.DataDir = dataDir
 			},
 		},
@@ -1181,7 +1181,7 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
 				`-datacenter=b`,
 				`-data-dir=` + dataDir,
 				`-join`, `c`, `-join=d`,
-				`-node-meta=c:d`,
+				`-node-meta=a:c`,
 				`-recursor`, `1.2.3.6`, `-recursor=5.6.7.10`,
 				`-serf-lan-bind=3.3.3.3`,
 				`-serf-wan-bind=4.4.4.4`,
@@ -1194,7 +1194,7 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
 				rt.SerfAdvertiseAddrWAN = tcpAddr("2.2.2.2:8302")
 				rt.Datacenter = "b"
 				rt.DNSRecursors = []string{"1.2.3.6", "5.6.7.10", "1.2.3.5", "5.6.7.9"}
-				rt.NodeMeta = map[string]string{"c": "d"}
+				rt.NodeMeta = map[string]string{"a": "c"}
 				rt.SerfBindAddrLAN = tcpAddr("3.3.3.3:8301")
 				rt.SerfBindAddrWAN = tcpAddr("4.4.4.4:8302")
 				rt.StartJoinAddrsLAN = []string{"c", "d", "a", "b"}