Reject YAML keys that collide after JSON conversion

key_collision_test.go

@@ -0,0 +1,60 @@
+package yaml
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+func TestRejectCollidingJSONMapKeys(t *testing.T) {
+	for _, test := range []struct {
+		name, input, key string
+	}{
+		{"fuzz input", "  0:\n  7:\n  .0:\n   02", "0"},
+		{"integer and string", "0x1: integer\n'1': string\n", "1"},
+		{"boolean and string", "TRUE: boolean\n\"true\": string\n", "true"},
+		{"nested mapping", "nested: {1.0: number, '1': string}\n", "1"},
+		{"sequence mapping", "- {1.0: number, '1': string}\n", "1"},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			want := fmt.Sprintf("multiple YAML keys map to JSON key %q", test.key)
+			for _, origin := range []bool{false, true} {
+				t.Run(fmt.Sprintf("origin=%t", origin), func(t *testing.T) {
+					var out any
+					_, err := Unmarshal([]byte(test.input), &out, DecodeOpts{Origin: OriginOpt{Enabled: origin}})
+					if err == nil || !strings.Contains(err.Error(), want) {
+						t.Fatalf("Unmarshal error = %v, want %q", err, want)
+					}
+				})
+			}
+			if _, err := YAMLToJSON([]byte(test.input)); err == nil || !strings.Contains(err.Error(), want) {
+				t.Fatalf("YAMLToJSON error = %v, want %q", err, want)
+			}
+		})
+	}
+}
+
+func TestDistinctJSONMapKeys(t *testing.T) {
+	for _, test := range []struct {
+		name, input, want string
+	}{
+		{"numeric keys", "1: one\n2: two\n", `{"1":"one","2":"two"}`},
+		{"distinct strings", "'0': one\n'0.0': two\n", `{"0":"one","0.0":"two"}`},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			for _, origin := range []bool{false, true} {
+				var out any
+				if _, err := Unmarshal([]byte(test.input), &out, DecodeOpts{Origin: OriginOpt{Enabled: origin}}); err != nil {
+					t.Fatalf("Unmarshal with origin=%t: %v", origin, err)
+				}
+			}
+			out, err := YAMLToJSON([]byte(test.input))
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(out) != test.want {
+				t.Fatalf("YAMLToJSON = %s, want %s", out, test.want)
+			}
+		})
+	}
+}

yaml.go

@@ -334,6 +334,9 @@ func convertToJSONableObject(yamlObj interface{}, jsonTarget *reflect.Value) (in
 				return nil, fmt.Errorf("unsupported map key of type: %s, key: %+#v, value: %+#v",
 					reflect.TypeOf(k), k, v)
 			}
+			if _, exists := strMap[keyString]; exists {
+				return nil, fmt.Errorf("multiple YAML keys map to JSON key %q", keyString)
+			}
 			strMap[keyString] = v
 		}
 		// replace yamlObj with our new string map