From 9a8facd7042f9fc93b0e1e1c3eea38fa0a6c3147 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Edwin=20T=C3=B6r=C3=B6k?= <edwin@etorok.net>
Date: Tue, 16 Jan 2024 23:32:13 +0000
Subject: [PATCH] Avoid infinite loop in lexer on unclosed code block
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An unclosed code block will cause the lexer to loop infinitely in the
'block' rule, because 'eof' is part of the 'eol' rule and it'll keep
matching the last rule.

Add a separate rule for eof that terminates immediately,
the way the first rule was written it would expect closing quotes after
eof which would never match eof.

Signed-off-by: Edwin Török <edwin@etorok.net>
---
 lib/lexer_mdx.mll                                    |  3 ++-
 test/bin/mdx-test/expect/dune.inc                    | 12 ++++++++++++
 test/bin/mdx-test/expect/unclosed-block/test-case.md |  7 +++++++
 .../expect/unclosed-block/test-case.md.expected      |  8 ++++++++
 4 files changed, 29 insertions(+), 1 deletion(-)
 create mode 100644 test/bin/mdx-test/expect/unclosed-block/test-case.md
 create mode 100644 test/bin/mdx-test/expect/unclosed-block/test-case.md.expected

diff --git a/lib/lexer_mdx.mll b/lib/lexer_mdx.mll
index 683abc818..960d087f4 100644
--- a/lib/lexer_mdx.mll
+++ b/lib/lexer_mdx.mll
@@ -56,7 +56,8 @@ rule text section = parse
         `Text str :: text section lexbuf }
 
 and block = parse
-  | eof | ws* as end_pad "```" ws* eol
+  | eof { [""] }
+  | ws* as end_pad "```" ws* eol
     { newline lexbuf;
       [end_pad] }
   | ([^'\n']* as str) eol
diff --git a/test/bin/mdx-test/expect/dune.inc b/test/bin/mdx-test/expect/dune.inc
index f489a3e2e..82bdf5887 100644
--- a/test/bin/mdx-test/expect/dune.inc
+++ b/test/bin/mdx-test/expect/dune.inc
@@ -575,6 +575,18 @@
  (alias runtest)
  (action (diff trailing-whitespaces/test-case.md.expected trailing-whitespaces.actual)))
 
+(rule
+ (target unclosed-block.actual)
+ (deps (package mdx) (source_tree unclosed-block))
+ (action
+  (with-stdout-to %{target}
+   (chdir unclosed-block
+    (run ocaml-mdx test --output - test-case.md)))))
+
+(rule
+ (alias runtest)
+ (action (diff unclosed-block/test-case.md.expected unclosed-block.actual)))
+
 (rule
  (target warnings.actual)
  (deps (package mdx) (source_tree warnings))
diff --git a/test/bin/mdx-test/expect/unclosed-block/test-case.md b/test/bin/mdx-test/expect/unclosed-block/test-case.md
new file mode 100644
index 000000000..3b1b42a10
--- /dev/null
+++ b/test/bin/mdx-test/expect/unclosed-block/test-case.md
@@ -0,0 +1,7 @@
+Here is a good block:
+
+```ocaml
+```
+
+And here is one that is not closed, this should not cause an infinite loop in the lexer:
+```
diff --git a/test/bin/mdx-test/expect/unclosed-block/test-case.md.expected b/test/bin/mdx-test/expect/unclosed-block/test-case.md.expected
new file mode 100644
index 000000000..14a4ff194
--- /dev/null
+++ b/test/bin/mdx-test/expect/unclosed-block/test-case.md.expected
@@ -0,0 +1,8 @@
+Here is a good block:
+
+```ocaml
+```
+
+And here is one that is not closed, this should not cause an infinite loop in the lexer:
+```
+```