Revert error message changes

Changes in PR 65 modified error messages. While some of the changes read better,
also produced duplicate prefixes (like "error converting YAML to JSON: error converting YAML to JSON:").

Even the improvements broke downstream unit tests relying on exact prefix matching.

Reverting the error message changes before tagging a new release to avoid disrupting consumers
until we consider the impact of these changes more thoroughly.

Author: liggitt

err_test.go

@@ -0,0 +1,130 @@
+/*
+Copyright 2023 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package yaml
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestErrors(t *testing.T) {
+	type Into struct {
+		Map map[string]interface{} `json:"map"`
+		Int int32                  `json:"int"`
+	}
+
+	testcases := []struct {
+		Name                   string
+		Data                   string
+		UnmarshalPrefix        string
+		UnmarshalStrictPrefix  string
+		YAMLToJSONPrefix       string
+		YAMLToJSONStrictPrefix string
+	}{
+		{
+			Name:                   "unmarshal syntax",
+			Data:                   `map: {`,
+			UnmarshalPrefix:        `error converting YAML to JSON: yaml: line 1: `,
+			UnmarshalStrictPrefix:  `error converting YAML to JSON: yaml: line 1: `,
+			YAMLToJSONPrefix:       `yaml: line 1: `,
+			YAMLToJSONStrictPrefix: `yaml: line 1: `,
+		},
+		{
+			Name:                   "unmarshal type",
+			Data:                   `map: ""`,
+			UnmarshalPrefix:        `error unmarshaling JSON: while decoding JSON: json: `,
+			UnmarshalStrictPrefix:  `error unmarshaling JSON: while decoding JSON: json: `,
+			YAMLToJSONPrefix:       ``,
+			YAMLToJSONStrictPrefix: ``,
+		},
+		{
+			Name:                   "unmarshal unknown",
+			Data:                   `unknown: {}`,
+			UnmarshalPrefix:        ``,
+			UnmarshalStrictPrefix:  `error unmarshaling JSON: while decoding JSON: json: `,
+			YAMLToJSONPrefix:       ``,
+			YAMLToJSONStrictPrefix: ``,
+		},
+		{
+			Name: "unmarshal duplicate",
+			Data: `
+int: 0
+int: 0`,
+			UnmarshalPrefix:        ``,
+			UnmarshalStrictPrefix:  `error converting YAML to JSON: yaml: `,
+			YAMLToJSONPrefix:       ``,
+			YAMLToJSONStrictPrefix: `yaml: unmarshal errors:`,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.Name, func(t *testing.T) {
+			v := Into{}
+			if err := Unmarshal([]byte(tc.Data), &v); err == nil {
+				if len(tc.UnmarshalPrefix) > 0 {
+					t.Fatal("expected err")
+				}
+			} else {
+				if len(tc.UnmarshalPrefix) == 0 {
+					t.Fatalf("unexpected err %v", err)
+				}
+				if !strings.HasPrefix(err.Error(), tc.UnmarshalPrefix) {
+					t.Fatalf("expected '%s' to start with '%s'", err.Error(), tc.UnmarshalPrefix)
+				}
+			}
+
+			if err := UnmarshalStrict([]byte(tc.Data), &v); err == nil {
+				if len(tc.UnmarshalStrictPrefix) > 0 {
+					t.Fatal("expected err")
+				}
+			} else {
+				if len(tc.UnmarshalStrictPrefix) == 0 {
+					t.Fatalf("unexpected err %v", err)
+				}
+				if !strings.HasPrefix(err.Error(), tc.UnmarshalStrictPrefix) {
+					t.Fatalf("expected '%s' to start with '%s'", err.Error(), tc.UnmarshalStrictPrefix)
+				}
+			}
+
+			if _, err := YAMLToJSON([]byte(tc.Data)); err == nil {
+				if len(tc.YAMLToJSONPrefix) > 0 {
+					t.Fatal("expected err")
+				}
+			} else {
+				if len(tc.YAMLToJSONPrefix) == 0 {
+					t.Fatalf("unexpected err %v", err)
+				}
+				if !strings.HasPrefix(err.Error(), tc.YAMLToJSONPrefix) {
+					t.Fatalf("expected '%s' to start with '%s'", err.Error(), tc.YAMLToJSONPrefix)
+				}
+			}
+
+			if _, err := YAMLToJSONStrict([]byte(tc.Data)); err == nil {
+				if len(tc.YAMLToJSONStrictPrefix) > 0 {
+					t.Fatal("expected err")
+				}
+			} else {
+				if len(tc.YAMLToJSONStrictPrefix) == 0 {
+					t.Fatalf("unexpected err %v", err)
+				}
+				if !strings.HasPrefix(err.Error(), tc.YAMLToJSONStrictPrefix) {
+					t.Fatalf("expected '%s' to start with '%s'", err.Error(), tc.YAMLToJSONStrictPrefix)
+				}
+			}
+		})
+	}
+}

yaml.go

@@ -91,7 +91,10 @@ func jsonUnmarshal(reader io.Reader, obj interface{}, opts ...JSONOpt) error {
 	for _, opt := range opts {
 		d = opt(d)
 	}
-	return d.Decode(obj)
+	if err := d.Decode(&obj); err != nil {
+		return fmt.Errorf("while decoding JSON: %v", err)
+	}
+	return nil
 }
 
 // JSONToYAML converts JSON to YAML. Notable implementation details:
@@ -110,13 +113,13 @@ func JSONToYAML(j []byte) ([]byte, error) {
 	// number type, so we can preserve number type throughout this process.
 	err := yaml.Unmarshal(j, &jsonObj)
 	if err != nil {
-		return nil, fmt.Errorf("error converting JSON to YAML: %w", err)
+		return nil, err
 	}
 
 	// Marshal this object into YAML.
 	yamlBytes, err := yaml.Marshal(jsonObj)
 	if err != nil {
-		return nil, fmt.Errorf("error converting JSON to YAML: %w", err)
+		return nil, err
 	}
 
 	return yamlBytes, nil
@@ -155,7 +158,7 @@ func yamlToJSONTarget(yamlBytes []byte, jsonTarget *reflect.Value, unmarshalFn f
 	var yamlObj interface{}
 	err := unmarshalFn(yamlBytes, &yamlObj)
 	if err != nil {
-		return nil, fmt.Errorf("error converting YAML to JSON: %w", err)
+		return nil, err
 	}
 
 	// YAML objects are not completely compatible with JSON objects (e.g. you
@@ -164,13 +167,13 @@ func yamlToJSONTarget(yamlBytes []byte, jsonTarget *reflect.Value, unmarshalFn f
 	// incompatibilties happen along the way.
 	jsonObj, err := convertToJSONableObject(yamlObj, jsonTarget)
 	if err != nil {
-		return nil, fmt.Errorf("error converting YAML to JSON: %w", err)
+		return nil, err
 	}
 
 	// Convert this object to JSON and return the data.
 	jsonBytes, err := json.Marshal(jsonObj)
 	if err != nil {
-		return nil, fmt.Errorf("error converting YAML to JSON: %w", err)
+		return nil, err
 	}
 	return jsonBytes, nil
 }