[confmap] - add a more targeted version of append-merging strategy

.chloggen/confmap-append-merge-components.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confmap
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Update the behavior of the confmap.enableMergeAppendOption feature gate to merge only component lists.
+
+# One or more tracking issues or pull requests related to the change
+issues: [12926]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

cmd/mdatagen/go.mod

@@ -37,6 +37,7 @@ require (
 	github.com/go-logr/logr v1.4.2 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect

cmd/otelcorecol/go.mod

@@ -47,6 +47,7 @@ require (
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-ole/go-ole v1.2.6 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/snappy v1.0.0 // indirect
 	github.com/google/uuid v1.6.0 // indirect

confmap/go.mod

@@ -4,6 +4,7 @@ go 1.23.0
 
 require (
 	github.com/go-viper/mapstructure/v2 v2.2.1
+	github.com/gobwas/glob v0.2.3
 	github.com/knadh/koanf/maps v0.1.2
 	github.com/knadh/koanf/providers/confmap v1.0.0
 	github.com/knadh/koanf/v2 v2.2.0

confmap/internal/e2e/go.mod

@@ -13,6 +13,7 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
 	github.com/knadh/koanf/providers/confmap v1.0.0 // indirect

confmap/merge.go

@@ -5,47 +5,70 @@ package confmap // import "go.opentelemetry.io/collector/confmap"
 
 import (
 	"reflect"
+
+	"github.com/gobwas/glob"
+	"github.com/knadh/koanf/maps"
 )
 
 func mergeAppend(src, dest map[string]any) error {
 	// mergeAppend recursively merges the src map into the dest map (left to right),
 	// modifying and expanding the dest map in the process.
-	// This function does not overwrite lists, and ensures that the final value is a name-aware
-	// copy of lists from src and dest.
+	// This function does not overwrite component lists, and ensures that the
+	// final value is a name-aware copy of lists from src and dest.
 
-	for sKey, sVal := range src {
-		dVal, dOk := dest[sKey]
-		if !dOk {
-			// key is not present in destination config. Hence, add it to destination map
-			dest[sKey] = sVal
-			continue
+	// Compile the globs once
+	patterns := []string{
+		"service::extensions",
+		"service::**::receivers",
+		"service::**::exporters",
+	}
+	var globs []glob.Glob
+	for _, p := range patterns {
+		if g, err := glob.Compile(p); err == nil {
+			globs = append(globs, g)
 		}
+	}
 
-		srcVal := reflect.ValueOf(sVal)
-		destVal := reflect.ValueOf(dVal)
+	// Flatten both source and destination maps
+	srcFlat, _ := maps.Flatten(src, []string{}, KeyDelimiter)
+	destFlat, _ := maps.Flatten(dest, []string{}, KeyDelimiter)
 
-		if destVal.Kind() != srcVal.Kind() {
-			// different kinds. Override the destination map
-			dest[sKey] = sVal
+	for sKey, sVal := range srcFlat {
+		if !isMatch(sKey, globs) {
 			continue
 		}
 
-		switch srcVal.Kind() {
-		case reflect.Array, reflect.Slice:
-			// both of them are array. Merge them
-			dest[sKey] = mergeSlice(srcVal, destVal)
-		case reflect.Map:
-			// both of them are maps. Recursively call the mergeAppend
-			_ = mergeAppend(sVal.(map[string]any), dVal.(map[string]any))
-		default:
-			// any other datatype. Override the destination map
-			dest[sKey] = sVal
+		dVal, dOk := destFlat[sKey]
+		if !dOk {
+			continue // Let maps.Merge handle missing keys
+		}
+
+		srcVal := reflect.ValueOf(sVal)
+		destVal := reflect.ValueOf(dVal)
+
+		// Only merge if the value is a slice or array; let maps.Merge handle other types
+		if srcVal.Kind() == reflect.Slice || srcVal.Kind() == reflect.Array {
+			srcFlat[sKey] = mergeSlice(srcVal, destVal)
 		}
 	}
 
+	// Unflatten and merge
+	mergedSrc := maps.Unflatten(srcFlat, KeyDelimiter)
+	maps.Merge(mergedSrc, dest)
+
 	return nil
 }
 
+// isMatch checks if a key matches any glob in the list
+func isMatch(key string, globs []glob.Glob) bool {
+	for _, g := range globs {
+		if g.Match(key) {
+			return true
+		}
+	}
+	return false
+}
+
 func mergeSlice(src, dest reflect.Value) any {
 	slice := reflect.MakeSlice(src.Type(), 0, src.Cap()+dest.Cap())
 	for i := 0; i < dest.Len(); i++ {

confmap/provider/envprovider/go.mod

@@ -12,6 +12,7 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
 	github.com/knadh/koanf/providers/confmap v1.0.0 // indirect

confmap/provider/fileprovider/go.mod

@@ -11,6 +11,7 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
 	github.com/knadh/koanf/providers/confmap v1.0.0 // indirect

confmap/provider/httpprovider/go.mod

@@ -11,6 +11,7 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
 	github.com/knadh/koanf/providers/confmap v1.0.0 // indirect

confmap/provider/httpsprovider/go.mod

@@ -11,6 +11,7 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
 	github.com/knadh/koanf/providers/confmap v1.0.0 // indirect

confmap/provider/yamlprovider/go.mod

@@ -11,6 +11,7 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.2.1 // indirect
+	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect
 	github.com/knadh/koanf/providers/confmap v1.0.0 // indirect

confmap/testdata/config2.yaml

@@ -0,0 +1,7 @@
+service:
+    extensions: [nop2]
+    pipelines:
+        traces:
+            receivers: [nop2]
+            processors: [nop]
+            exporters: [nop2]