Eliminate panics and enable the missing panics docs check

parser/CHANGELOG.md

@@ -16,6 +16,8 @@
 - `Yaml::load_from_bytes()` is now available.
   ([#156](https://github.com/chyh1990/yaml-rust/pull/156))
 
+- The parser and scanner now return Err() instead of calling panic.
+
 **Development**:
 
 - The documentation was updated to include a security note mentioning that

parser/src/lib.rs

@@ -33,11 +33,7 @@
 #![cfg_attr(feature = "cargo-clippy", warn(clippy::pedantic))]
 #![cfg_attr(
     feature = "cargo-clippy",
-    allow(
-        clippy::should_implement_trait,
-        clippy::missing_errors_doc,
-        clippy::missing_panics_doc,
-    )
+    allow(clippy::should_implement_trait, clippy::missing_errors_doc,)
 )]
 
 extern crate hashlink;

parser/src/parser.rs

@@ -306,7 +306,9 @@ impl<T: Iterator<Item = char>> Parser<T> {
     ) -> Result<(), ScanError> {
         if !self.scanner.stream_started() {
             let (ev, mark) = self.next()?;
-            assert_eq!(ev, Event::StreamStart);
+            if ev != Event::StreamStart {
+                return Err(ScanError::new(mark, "did not find expected <stream-start>"));
+            }
             recv.on_event(ev, mark);
         }
 
@@ -337,7 +339,12 @@ impl<T: Iterator<Item = char>> Parser<T> {
         mark: Marker,
         recv: &mut R,
     ) -> Result<(), ScanError> {
-        assert_eq!(first_ev, Event::DocumentStart);
+        if first_ev != Event::DocumentStart {
+            return Err(ScanError::new(
+                mark,
+                "did not find expected <document-start>",
+            ));
+        }
         recv.on_event(first_ev, mark);
 
         let (ev, mark) = self.next()?;

parser/src/scanner.rs

@@ -716,7 +716,12 @@ impl<T: Iterator<Item = char>> Scanner<T> {
         if !self.token_available {
             self.fetch_more_tokens()?;
         }
-        let t = self.tokens.pop_front().unwrap();
+        let Some(t) = self.tokens.pop_front() else {
+            return Err(ScanError::new(
+                self.mark,
+                "did not find expected next token",
+            ));
+        };
         self.token_available = false;
         self.tokens_parsed += 1;