[confmap]- Implement yaml tags based strategy for merge append mode

.chloggen/13256.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: pkg/confmap
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add YAML tag based list merging strategy.
+
+# One or more tracking issues or pull requests related to the change
+issues: [8754]
+
+# (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

@@ -38,7 +38,6 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // 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

@@ -47,7 +47,6 @@ 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 v2.4.0 // 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/go-tpm v0.9.6 // indirect

config/configgrpc/go.mod

@@ -35,7 +35,6 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
-	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/golang/snappy v0.0.4 // indirect
 	github.com/google/go-tpm v0.9.6 // indirect

config/confighttp/go.mod

@@ -38,7 +38,6 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
-	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/google/go-tpm v0.9.6 // indirect
 	github.com/google/uuid v1.6.0 // indirect

config/confighttp/xconfighttp/go.mod

@@ -19,7 +19,6 @@ require (
 	github.com/go-logr/logr v1.4.3 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // 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/go-tpm v0.9.6 // indirect

config/configoptional/go.mod

@@ -12,7 +12,6 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // 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

config/configtls/go.mod

@@ -14,7 +14,6 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
-	github.com/gobwas/glob v0.2.3 // indirect
 	github.com/google/go-tpm-tools v0.4.4 // indirect
 	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.2 // indirect

confmap/README.md

@@ -96,11 +96,32 @@ The `Resolve` method proceeds in the following steps:
 #### (Experimental) Append merging strategy for lists
 
 You can opt-in to experimentally combine slices instead of discarding the existing ones by enabling the `confmap.enableMergeAppendOption` feature flag. Lists are appended in the order in which they appear in their configuration sources.
-This will **not** become the default in the future, we are still deciding how this should be configured and want your feedback on [this issue](https://github.com/open-telemetry/opentelemetry-collector/issues/8754).
+This lets you combine slices from multiple configuration sources, with control over ordering, duplicates, and targeted merge paths using YAML tags or URI query parameters.
+
+#### How It Works
+
+Annotate any list in your YAML config with a custom tag (URI-style parameters) to specify how it should be merged.
+
+**Tag format:**  
+`!mode=append&duplicates=false`
+
+**Options:**
+- `mode`: `append` (default)
+- `duplicates`: `true` or `false` (default: `false`)
+  - Setting this to `true` allows duplicate entries in the final list.
+
+> [!WARNING]
+> Specifying incorrect values in YAML tags will result in fallback to the default behavior.
+
+#### Default Behavior (Override)
+
+If you do **NOT** specify any merge options or tags, lists are merged using the default override behavior (the last config wins).
 
 ##### Example
-Consider the following configs,
 
+Suppose you have the following configurations:
+
+**main.yaml**
 ```yaml
 # main.yaml
 receivers:
@@ -126,24 +147,20 @@ service:
   extensions: [ file_storage ]
 ```
 
-
+**extra_extension.yaml**
 ```yaml
-# extra_extension.yaml
 extensions:
   healthcheckv2:
-
 service:
-  extensions: [ healthcheckv2 ]
-  pipelines:
-    traces:
+  extensions: !mode=append [healthcheckv2]
 ```
 
-If you run the Collector with following command,
-```
+If you run the Collector with:
+```bash
 otelcol --config=main.yaml --config=extra_extension.yaml --feature-gates=confmap.enableMergeAppendOption
 ```
-then the final configuration after config resolution will look like following:
 
+The result after merging will be:
 ```yaml
 # main.yaml
 receivers:
@@ -169,10 +186,10 @@ service:
   extensions: [ file_storage, healthcheckv2 ]
 ```
 
-Notice that the `service::extensions` list is a combination of both configurations. By default, the value of the last configuration source passed, `extra_extension`, would be used, so the extensions list would be: `service::extensions: [healthcheckv2]`.
+Notice how the `service::extensions` list is a combination of both configurations, preserving both values.
 
 > [!NOTE]
-> By enabling this feature gate, all the lists in the given configuration will be merged. 
+> By enabling this feature gate, only the lists annotated with YAML merge tags will be merged according to your specified strategy. Unannotated lists will continue to use the default override behavior (last list wins).
 
 ### Watching for Updates
 After the configuration was processed, the `Resolver` can be used as a single point to watch for updates in the

confmap/go.mod

@@ -4,7 +4,6 @@ go 1.24.0
 
 require (
 	github.com/go-viper/mapstructure/v2 v2.4.0
-	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 v2.3.0

confmap/internal/conf.go

@@ -32,6 +32,8 @@ type Conf struct {
 	// isNil is true if this Conf was created from a nil field, as opposed to an empty map.
 	// AllKeys must return an empty slice if this is true.
 	isNil bool
+
+	mergeOpts map[string]*MergeOptions
 }
 
 // New creates a new empty confmap.Conf instance.
@@ -51,6 +53,11 @@ func NewFromStringMap(data map[string]any) *Conf {
 	return p
 }
 
+func (l *Conf) WithMergeOptions(opt map[string]*MergeOptions) *Conf {
+	l.mergeOpts = opt
+	return l
+}
+
 // Unmarshal unmarshalls the config into a struct using the given options.
 // Tags on the fields of the structure must be properly set.
 func (l *Conf) Unmarshal(result any, opts ...UnmarshalOption) error {
@@ -122,7 +129,7 @@ func (l *Conf) Delete(key string) bool {
 // For example, if listA = [extension1, extension2] and listB = [extension1, extension3],
 // the resulting list will be [extension1, extension2, extension3].
 func (l *Conf) mergeAppend(in *Conf) error {
-	err := l.k.Load(confmap.Provider(in.ToStringMap(), ""), nil, koanf.WithMergeFunc(mergeAppend))
+	err := l.k.Load(confmap.Provider(in.ToStringMap(), ""), nil, koanf.WithMergeFunc(mergeAppend(in.mergeOpts)))
 	if err != nil {
 		return err
 	}

confmap/internal/e2e/go.mod

@@ -13,7 +13,6 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // 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