tftypes: Clarified ValueFromJSON error messaging with object attribute key issues

.changelog/214.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+tftypes: Clarified `ValueFromJSON` error messaging with object attribute key issues
+```

tftypes/value_json.go

@@ -435,20 +435,19 @@ func jsonUnmarshalObject(buf []byte, attrTypes map[string]Type, p *AttributePath
 
 	vals := map[string]Value{}
 	for dec.More() {
-		innerPath := p.WithElementKeyValue(NewValue(String, UnknownValue))
 		tok, err := dec.Token()
 		if err != nil {
-			return Value{}, innerPath.NewErrorf("error reading token: %w", err)
+			return Value{}, p.NewErrorf("error reading object attribute key token: %w", err)
 		}
 		key, ok := tok.(string)
 		if !ok {
-			return Value{}, innerPath.NewErrorf("object attribute key was %T, not string", tok)
+			return Value{}, p.NewErrorf("object attribute key was %T with value %v, not string", tok, tok)
 		}
+		innerPath := p.WithAttributeName(key)
 		attrType, ok := attrTypes[key]
 		if !ok {
 			return Value{}, innerPath.NewErrorf("unsupported attribute %q", key)
 		}
-		innerPath = p.WithAttributeName(key)
 
 		var rawVal json.RawMessage
 		err = dec.Decode(&rawVal)

tftypes/value_json_test.go

@@ -1,6 +1,7 @@
 package tftypes
 
 import (
+	"fmt"
 	"math/big"
 	"testing"
 
@@ -10,9 +11,10 @@ import (
 func TestValueFromJSON(t *testing.T) {
 	t.Parallel()
 	type testCase struct {
-		value Value
-		typ   Type
-		json  string
+		value         Value
+		typ           Type
+		json          string
+		expectedError error
 	}
 	tests := map[string]testCase{
 		// Primitives
@@ -211,6 +213,30 @@ func TestValueFromJSON(t *testing.T) {
 			},
 			json: `{}`,
 		},
+		"object-attribute-key-token-error": {
+			value: Value{},
+			typ: Object{
+				AttributeTypes: map[string]Type{},
+			},
+			json: `{{}}`,
+			expectedError: AttributePathError{
+				Path: NewAttributePath(),
+				err:  fmt.Errorf("error reading object attribute key token: invalid character '{'"),
+			},
+		},
+		"object-attribute-key-missing-error": {
+			value: Value{},
+			typ: Object{
+				AttributeTypes: map[string]Type{
+					"test": String,
+				},
+			},
+			json: `{"not-test": "test-value"}`,
+			expectedError: AttributePathError{
+				Path: NewAttributePath().WithAttributeName("not-test"),
+				err:  fmt.Errorf("unsupported attribute \"not-test\""),
+			},
+		},
 		"object-of-bool_number": {
 			value: NewValue(Object{
 				AttributeTypes: map[string]Type{
@@ -371,8 +397,8 @@ func TestValueFromJSON(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			t.Parallel()
 			val, err := ValueFromJSON([]byte(test.json), test.typ)
-			if err != nil {
-				t.Fatalf("unexpected error unmarshaling: %s", err)
+			if diff := cmp.Diff(test.expectedError, err); diff != "" {
+				t.Errorf("unexpected error difference: %s", diff)
 			}
 			if diff := cmp.Diff(test.value, val); diff != "" {
 				t.Errorf("Unexpected results (-wanted +got): %s", diff)