$match

README.md

@@ -99,7 +99,6 @@ $match:
   metadata:
     name: myService
 ```
-* K8s paths: If `kind` and `metadata.name` are present, they are used as match keys.
 * Ordering: Stream position is used to match documents.
 
 ## Merge Behavior

bkl.go

@@ -20,6 +20,7 @@ var (
 	ErrInvalidDirective = fmt.Errorf("invalid directive (%w)", Err)
 	ErrInvalidType      = fmt.Errorf("invalid type (%w)", Err)
 	ErrMissingFile      = fmt.Errorf("missing file (%w)", Err)
+	ErrNoMatchFound     = fmt.Errorf("no document matched $match (%w)", Err)
 	ErrRequiredField    = fmt.Errorf("required field not set (%w)", Err)
 	ErrUnknownFormat    = fmt.Errorf("unknown format (%w)", Err)
 
@@ -90,6 +91,8 @@ func (p *Parser) MergePatch(index int, patch any) error {
 
 // MergeIndexBytes parses the supplied doc bytes as the format specified by ext
 // (file extension), then calls [MergePatch()].
+//
+// index is taken as a hint but can be overridden by $match.
 func (p *Parser) MergeIndexBytes(index int, doc []byte, ext string) error {
 	f, found := formatByExtension[ext]
 	if !found {
@@ -101,6 +104,26 @@ func (p *Parser) MergeIndexBytes(index int, doc []byte, ext string) error {
 		return fmt.Errorf("%w / %w", err, ErrDecode)
 	}
 
+	if patchMap, ok := CanonicalizeType(patch).(map[string]any); ok {
+		m, found := patchMap["$match"]
+		if found {
+			delete(patchMap, "$match")
+
+			index = -1
+
+			for i, doc := range p.docs {
+				if Match(doc, m) {
+					index = i
+					break
+				}
+			}
+
+			if index == -1 {
+				return fmt.Errorf("%#v: %w", m, ErrNoMatchFound)
+			}
+		}
+	}
+
 	err = p.MergePatch(index, patch)
 	if err != nil {
 		return err

tests/match-map/a.b.yaml

@@ -0,0 +1,7 @@
+$match:
+  b: 2
+c: 3
+---
+$match:
+  a: 1
+d: 4

tests/match-map/a.yaml

@@ -0,0 +1,3 @@
+a: 1
+---
+b: 2

tests/match-map/cmd

@@ -0,0 +1 @@
+bkl -f yaml a.b.yaml

tests/match-map/expected

@@ -0,0 +1,5 @@
+a: 1
+d: 4
+---
+b: 2
+c: 3