Fix some cases of overlapping $merge races

merge.go

@@ -2,8 +2,6 @@ package bkl
 
 import (
 	"fmt"
-
-	"github.com/gopatchy/bkl/polyfill"
 )
 
 func merge(dst any, src any) (any, error) {
@@ -40,13 +38,13 @@ func mergeMap(dst map[string]any, src any) (map[string]any, error) {
 }
 
 func mergeMapMap(dst map[string]any, src map[string]any) (map[string]any, error) {
-	replace, src := popMapBoolValue(src, "$replace", true)
-	if replace {
+	replace, found := getMapBoolValue(src, "$replace")
+	if found && replace {
+		delete(src, "$replace")
+
 		return src, nil
 	}
 
-	dst = polyfill.MapsClone(dst)
-
 	for k, v := range src {
 		existing, found := dst[k]
 

polyfill/with_go1_21.go

@@ -20,6 +20,10 @@ func SlicesClone[S ~[]E, E any](s S) S { //nolint:ireturn
 	return slices.Clone(s)
 }
 
+func SlicesDeleteFunc[S ~[]E, E any](s S, del func(E) bool) S { //nolint:ireturn
+	return slices.DeleteFunc(s, del)
+}
+
 func SlicesReverse[S ~[]E, E any](s S) {
 	slices.Reverse(s)
 }

polyfill/without_go1_21.go

@@ -36,6 +36,28 @@ func SlicesClone[S ~[]E, E any](s S) S { //nolint:ireturn
 	return append(S([]E{}), s...)
 }
 
+// Copied from go1.21 slices
+func SlicesDeleteFunc[S ~[]E, E any](s S, del func(E) bool) S { //nolint:ireturn
+	for i, v := range s {
+		if del(v) {
+			j := i
+
+			for i++; i < len(s); i++ {
+				v = s[i]
+
+				if !del(v) {
+					s[j] = v
+					j++
+				}
+			}
+
+			return s[:j]
+		}
+	}
+
+	return s
+}
+
 // Copied from go1.21 slices
 func SlicesReverse[S ~[]E, E any](s S) {
 	for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {

process.go

@@ -9,6 +9,8 @@ func Process(obj, mergeFrom any, mergeFromDocs []any) (any, error) {
 	return process(obj, mergeFrom, mergeFromDocs, 0)
 }
 
+// process() and descendants intentionally mutate obj to handle chained
+// references
 func process(obj, mergeFrom any, mergeFromDocs []any, depth int) (any, error) {
 	if depth > 1000 {
 		return nil, fmt.Errorf("%#v: %w", obj, ErrCircularRef)
@@ -30,8 +32,10 @@ func process(obj, mergeFrom any, mergeFromDocs []any, depth int) (any, error) {
 }
 
 func processMap(obj map[string]any, mergeFrom any, mergeFromDocs []any, depth int) (any, error) {
-	m, obj := popMapValue(obj, "$merge")
+	m := obj["$merge"]
 	if m != nil {
+		delete(obj, "$merge")
+
 		in, err := get(mergeFrom, mergeFromDocs, m)
 		if err != nil {
 			return nil, err
@@ -45,8 +49,10 @@ func processMap(obj map[string]any, mergeFrom any, mergeFromDocs []any, depth in
 		return process(next, mergeFrom, mergeFromDocs, depth)
 	}
 
-	m, obj = popMapValue(obj, "$replace")
+	m = obj["$replace"]
 	if m != nil {
+		delete(obj, "$replace")
+
 		next, err := get(mergeFrom, mergeFromDocs, m)
 		if err != nil {
 			return nil, err
@@ -55,27 +61,28 @@ func processMap(obj map[string]any, mergeFrom any, mergeFromDocs []any, depth in
 		return process(next, mergeFrom, mergeFromDocs, depth)
 	}
 
-	output, obj := popMapBoolValue(obj, "$output", false)
-	if output {
+	output, found := getMapBoolValue(obj, "$output")
+	if found && !output {
 		return nil, nil
 	}
 
-	encode, obj := popMapStringValue(obj, "$encode")
+	encode := getMapStringValue(obj, "$encode")
+	if encode != "" {
+		delete(obj, "$encode")
+	}
 
-	obj, err := filterMap(obj, func(k string, v any) (map[string]any, error) {
+	for k, v := range obj {
 		v2, err := process(v, mergeFrom, mergeFromDocs, depth)
 		if err != nil {
 			return nil, err
 		}
 
 		if v2 == nil {
-			return nil, nil
+			delete(obj, k)
+			continue
 		}
 
-		return map[string]any{k: v2}, nil
-	})
-	if err != nil {
-		return nil, err
+		obj[k] = v2
 	}
 
 	if encode != "" {

tests/merge-race/a.b.yaml

@@ -0,0 +1 @@
+$merge: c

tests/merge-race/a.yaml

@@ -0,0 +1,4 @@
+a: $required
+b: $merge:a
+c:
+  a: 1

tests/merge-race/cmd

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

tests/merge-race/expected

@@ -0,0 +1,4 @@
+a: 1
+b: 1
+c:
+  a: 1