Improve error messages when deserializing enums

Author: avandecreme

src/de.rs

@@ -1873,7 +1873,14 @@ 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);
 
@@ -1882,12 +1889,11 @@ 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![