Simplify code, have errors match CPython implementation.

parser/src/fstring.rs

@@ -29,39 +29,25 @@ impl<'a> FStringParser<'a> {
 
         while let Some(ch) = self.chars.next() {
             match ch {
-                '!' if delims.is_empty() => {
-                    let x = self.chars.next();
-                    if let Some('=') = x {
-                        expression.push(ch);
-                        expression.push('=');
-                    } else {
-                        if expression.is_empty() {
-                            return Err(EmptyExpression);
-                        }
+                '!' if delims.is_empty() && self.chars.peek() != Some(&'=') => {
+                    if expression.trim().is_empty() {
+                        return Err(EmptyExpression);
+                    }
 
-                        conversion = Some(match x {
-                            Some('s') => ConversionFlag::Str,
-                            Some('a') => ConversionFlag::Ascii,
-                            Some('r') => ConversionFlag::Repr,
-                            Some(_) => {
-                                return Err(InvalidConversionFlag);
-                            }
-                            None => {
-                                break;
-                            }
-                        });
-
-                        match self.chars.peek() {
-                            Some('}') => {
-                                continue;
-                            }
-                            Some(_) => {
-                                return Err(ExpectedRbrace);
-                            }
-                            None => {
-                                break;
-                            }
+                    conversion = Some(match self.chars.next() {
+                        Some('s') => ConversionFlag::Str,
+                        Some('a') => ConversionFlag::Ascii,
+                        Some('r') => ConversionFlag::Repr,
+                        Some(_) => {
+                            return Err(InvalidConversionFlag);
                         }
+                        None => {
+                            return Err(ExpectedRbrace);
+                        }
+                    });
+
+                    if self.chars.peek() != Some(&'}') {
+                        return Err(ExpectedRbrace);
                     }
                 }
                 ':' if delims.is_empty() => {
@@ -314,16 +300,23 @@ mod tests {
 
     #[test]
     fn test_parse_invalid_fstring() {
-        assert_eq!(parse_fstring("{"), Err(UnclosedLbrace));
-        assert_eq!(parse_fstring("}"), Err(UnopenedRbrace));
-        assert_eq!(parse_fstring("{5!a"), Err(UnclosedLbrace));
+        assert_eq!(parse_fstring("{5!a"), Err(ExpectedRbrace));
         assert_eq!(parse_fstring("{5!a1}"), Err(ExpectedRbrace));
+        assert_eq!(parse_fstring("{5!"), Err(ExpectedRbrace));
+
         assert_eq!(parse_fstring("abc{!a 'cat'}"), Err(EmptyExpression));
-        assert_eq!(parse_fstring("{!x}"), Err(EmptyExpression));
+        assert_eq!(parse_fstring("{!a"), Err(EmptyExpression));
+        assert_eq!(parse_fstring("{ !a}"), Err(EmptyExpression));
+
+        assert_eq!(parse_fstring("{5!}"), Err(InvalidConversionFlag));
+        assert_eq!(parse_fstring("{5!x}"), Err(InvalidConversionFlag));
 
         assert_eq!(parse_fstring("{a:{a:{b}}"), Err(ExpressionNestedTooDeeply));
+
         assert_eq!(parse_fstring("{a:b}}"), Err(UnopenedRbrace));
+        assert_eq!(parse_fstring("}"), Err(UnopenedRbrace));
         assert_eq!(parse_fstring("{a:{b}"), Err(UnclosedLbrace));
+        assert_eq!(parse_fstring("{"), Err(UnclosedLbrace));
 
         // TODO: check for InvalidExpression enum?
         assert!(parse_fstring("{class}").is_err());
@@ -333,6 +326,6 @@ mod tests {
     fn test_parse_fstring_not_equals() {
         let source = String::from("{1 != 2}");
         let parse_ast = parse_fstring(&source);
-        assert_ne!(parse_ast, Err(InvalidConversionFlag));
+        assert!(parse_ast.is_ok());
     }
 }