Improve error messages when deserializing enums

Author: avandecreme

src/de.rs

@@ -1879,7 +1879,14 @@ impl<'de, R: Read<'de>> de::Deserializer<'de> for &mut Deserializer<R> {
  Some(b'{') => {
  check_recursion! {
  self.eat_char();
- let ret = visitor.visit_enum(VariantAccess::new(self));
+ let ret = match tri!(self.parse_whitespace()) {
+ Some(b'}') => Err(self.fix_position(de::Error::invalid_value(
+ Unexpected::Other("empty map"),
+ &"enum variant",
+ ))),
+ Some(_) => visitor.visit_enum(VariantAccess::new(self)),
+ None => Err(self.error(ErrorCode::EofWhileParsingObject)),
+ };
  }
  let value = tri!(ret);
 
@@ -1888,12 +1895,11 @@ impl<'de, R: Read<'de>> de::Deserializer<'de> for &mut Deserializer<R> {
  self.eat_char();
  Ok(value)
  }
- Some(_) => Err(self.error(ErrorCode::ExpectedSomeValue)),
+ Some(_) => Err(self.error(ErrorCode::ExpectedObjectEnd)),
  None => Err(self.error(ErrorCode::EofWhileParsingObject)),
  }
  }
- Some(b'"') => visitor.visit_enum(UnitVariantAccess::new(self)),
- Some(_) => Err(self.peek_error(ErrorCode::ExpectedSomeValue)),
+ Some(_) => visitor.visit_enum(UnitVariantAccess::new(self)),
  None => Err(self.peek_error(ErrorCode::EofWhileParsingValue)),
  }
  }

src/error.rs

@@ -62,6 +62,7 @@ impl Error {
  ErrorCode::ExpectedColon
  | ErrorCode::ExpectedListCommaOrEnd
  | ErrorCode::ExpectedObjectCommaOrEnd
+ | ErrorCode::ExpectedObjectEnd
  | ErrorCode::ExpectedSomeIdent
  | ErrorCode::ExpectedSomeValue
  | ErrorCode::ExpectedDoubleQuote
@@ -261,6 +262,9 @@ pub(crate) enum ErrorCode {
  /// Expected this character to be either a `','` or a `'}'`.
  ExpectedObjectCommaOrEnd,
 
+ /// Expected this character to be `'}'`.
+ ExpectedObjectEnd,
+
  /// Expected to parse either a `true`, `false`, or a `null`.
  ExpectedSomeIdent,
 
@@ -358,6 +362,7 @@ impl Display for ErrorCode {
  ErrorCode::ExpectedColon => f.write_str("expected `:`"),
  ErrorCode::ExpectedListCommaOrEnd => f.write_str("expected `,` or `]`"),
  ErrorCode::ExpectedObjectCommaOrEnd => f.write_str("expected `,` or `}`"),
+ ErrorCode::ExpectedObjectEnd => f.write_str("expected `}`"),
  ErrorCode::ExpectedSomeIdent => f.write_str("expected ident"),
  ErrorCode::ExpectedSomeValue => f.write_str("expected value"),
  ErrorCode::ExpectedDoubleQuote => f.write_str("expected `\"`"),

tests/test.rs

@@ -70,6 +70,12 @@ enum Animal {
  AntHive(Vec<String>),
 }
 
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+enum BoardGame {
+ Chess,
+ Checkers,
+}
+
 #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
 struct Inner {
  a: (),
@@ -1304,12 +1310,15 @@ fn test_parse_option() {
 fn test_parse_enum_errors() {
  test_parse_err::<Animal>(
  &[
- ("{}", "expected value at line 1 column 2"),
- ("[]", "expected value at line 1 column 1"),
+ ("{}", "invalid value: empty map, expected enum variant at line 1 column 1"),
+ ("[]", "invalid type: sequence, expected variant identifier at line 1 column 0"),
+ ("true", "invalid type: boolean `true`, expected variant identifier at line 1 column 4"),
  ("\"unknown\"",
  "unknown variant `unknown`, expected one of `Dog`, `Frog`, `Cat`, `AntHive` at line 1 column 9"),
  ("{\"unknown\":null}",
  "unknown variant `unknown`, expected one of `Dog`, `Frog`, `Cat`, `AntHive` at line 1 column 10"),
+ ("{\"AntHive\": []", "EOF while parsing an object at line 1 column 14"),
+ ("{\"AntHive\": [],", "expected `}` at line 1 column 14"),
  ("{\"Dog\":", "EOF while parsing a value at line 1 column 7"),
  ("{\"Dog\":}", "expected value at line 1 column 8"),
  ("{\"Dog\":{}}", "invalid type: map, expected unit at line 1 column 7"),
@@ -1331,6 +1340,40 @@ fn test_parse_enum_errors() {
  );
 }
 
+#[test]
+fn test_parse_value_less_enum_errors() {
+ test_parse_err::<BoardGame>(&[
+ (
+ "1",
+ "invalid type: integer `1`, expected variant identifier at line 1 column 1",
+ ),
+ (
+ "null",
+ "invalid type: null, expected variant identifier at line 1 column 4",
+ ),
+ (
+ "true",
+ "invalid type: boolean `true`, expected variant identifier at line 1 column 4",
+ ),
+ (
+ "[]",
+ "invalid type: sequence, expected variant identifier at line 1 column 0",
+ ),
+ (
+ "{}",
+ "invalid value: empty map, expected enum variant at line 1 column 1",
+ ),
+ (
+ "{\"unknown\": \"unknown\"}",
+ "unknown variant `unknown`, expected `Chess` or `Checkers` at line 1 column 10",
+ ),
+ (
+ "{\"Chess\": \"unknown\"}",
+ "invalid type: string \"unknown\", expected unit at line 1 column 19",
+ ),
+ ]);
+}
+
 #[test]
 fn test_parse_enum() {
  test_parse_ok(vec![