Optimize text lexer with predictive parsing

src/text/de.rs

@@ -252,7 +252,7 @@ impl<'de, 'a, R: Read, E: Encoding> de::MapAccess<'de> for TextReaderMap<'a, R,
         V: DeserializeSeed<'de>,
     {
         let de = unsafe { &mut *(self.de as *mut _) };
-        let token = self.de.reader.read()?;
+        let token = self.de.reader.read_expect_equals()?;
         let deser = if let Token::Operator(op) = token {
             let new_token = self.de.reader.read()?;
             let mut deser = TextReaderTokenDeserializer::new(de, new_token);

src/text/reader.rs

@@ -681,6 +681,17 @@ where
         }
     }
 
+    #[inline]
+    pub(crate) fn read_expect_equals(&mut self) -> Result<Token, ReaderError> {
+        match self.buf.window().first() {
+            Some(b'=') => {
+                self.buf.advance(1);
+                Ok(Token::Operator(Operator::Equal))
+            }
+            _ => self.read(),
+        }
+    }
+
     /// Read a token, returning none when all the data has been consumed
     ///
     /// ```rust