From 3358629dd1da63be117716b33e8bf32a22c13db9 Mon Sep 17 00:00:00 2001
From: Ethiraric <ethiraric@gmail.com>
Date: Sat, 19 Oct 2024 04:14:50 +0200
Subject: [PATCH] Fix infinite loop on `{...`.

---
 parser/src/scanner.rs           | 20 +++++++++++++++-----
 parser/tests/issues.rs          | 11 +++++++++++
 parser/tests/yaml-test-suite.rs |  3 ++-
 3 files changed, 28 insertions(+), 6 deletions(-)

diff --git a/parser/src/scanner.rs b/parser/src/scanner.rs
index 3fcbeb0..0509181 100644
--- a/parser/src/scanner.rs
+++ b/parser/src/scanner.rs
@@ -2177,7 +2177,7 @@ impl<T: Input> Scanner<T> {
         loop {
             self.input.lookahead(4);
             if self.input.next_is_document_end()
-                || (self.input.next_is_document_start() && self.leading_whitespace)
+                || (self.leading_whitespace && self.input.next_is_document_start())
                 || self.input.peek() == '#'
             {
                 break;
@@ -2293,10 +2293,20 @@ impl<T: Input> Scanner<T> {
             self.allow_simple_key();
         }
 
-        Ok(Token(
-            Span::new(start_mark, end_mark),
-            TokenType::Scalar(TScalarStyle::Plain, string),
-        ))
+        if string.is_empty() {
+            // `fetch_plain_scalar` must absolutely consume at least one byte. Otherwise,
+            // `fetch_next_token` will never stop calling it. An empty plain scalar may happen with
+            // erroneous inputs such as "{...".
+            Err(ScanError::new_str(
+                start_mark,
+                "unexpected end of plain scalar",
+            ))
+        } else {
+            Ok(Token(
+                Span::new(start_mark, end_mark),
+                TokenType::Scalar(TScalarStyle::Plain, string),
+            ))
+        }
     }
 
     fn fetch_key(&mut self) -> ScanResult {
diff --git a/parser/tests/issues.rs b/parser/tests/issues.rs
index e8e9d38..d056d6f 100644
--- a/parser/tests/issues.rs
+++ b/parser/tests/issues.rs
@@ -214,6 +214,17 @@ fn test_issue14() {
     );
 }
 
+#[test]
+fn test_issue14_v2() {
+    let s = "{...";
+    let Err(error) = run_parser(s) else { panic!() };
+    assert_eq!(error.info(), "unexpected end of plain scalar");
+    assert_eq!(
+        error.to_string(),
+        "unexpected end of plain scalar at byte 1 line 1 column 2"
+    );
+}
+
 #[test]
 fn test_issue13() {
     // The following input creates an infinite loop.
diff --git a/parser/tests/yaml-test-suite.rs b/parser/tests/yaml-test-suite.rs
index 554bac3..866ba16 100644
--- a/parser/tests/yaml-test-suite.rs
+++ b/parser/tests/yaml-test-suite.rs
@@ -94,7 +94,8 @@ fn load_tests_from_file(entry: &DirEntry) -> Result<Vec<Test<YamlTest>>> {
     let test_name = file_name
         .strip_suffix(".yaml")
         .ok_or("unexpected filename")?;
-    let tests = Yaml::load_from_str(&fs::read_to_string(entry.path())?)?;
+    let tests = Yaml::load_from_str(&fs::read_to_string(entry.path())?)
+        .map_err(|e| format!("While reading {file_name}: {e}"))?;
     let tests = tests[0].as_vec().ok_or("no test list found in file")?;
 
     let mut result = vec![];