From 09b9a73c2d8abcd8d459a0e412fa4bef5f4ded95 Mon Sep 17 00:00:00 2001
From: nsfisis <nsfisis@gmail.com>
Date: Thu, 8 Jan 2026 02:44:13 +0900
Subject: fix: infinite loop when tokenizing "#include HEADER_MACRO"

---
 src/tokenize.c          | 10 ++++++++++
 tests/include_errors.sh | 11 +++++++++++
 2 files changed, 21 insertions(+)

diff --git a/src/tokenize.c b/src/tokenize.c
index 1e7a8df..26c6e13 100644
--- a/src/tokenize.c
+++ b/src/tokenize.c
@@ -361,6 +361,16 @@ static void do_tokenize_all(Lexer* l) {
         } else if (c == '\n') {
             infile_next_char(l->src);
             tok->kind = TokenKind_newline;
+
+            // Reset expect_header_name at the end of line. It handles cases like:
+            //
+            // #ifdef ADDITIONAL_HEADER
+            // #include ADDITIONAL_HEADER
+            // #endif
+            //
+            // Even if ADDITIONAL_HEADER is undefined, this include directive line is tokenized. If the flag were not
+            // reset, the next occurrence of '<' or '"' would be recognized as part of a header name.
+            l->expect_header_name = false;
         } else if (isspace(c)) {
             while (isspace((c = infile_peek_char(l->src)))) {
                 if (c == '\n')
diff --git a/tests/include_errors.sh b/tests/include_errors.sh
index 3ac546f..e0f856e 100644
--- a/tests/include_errors.sh
+++ b/tests/include_errors.sh
@@ -50,3 +50,14 @@ test_compile_error <<'EOF'
 #include <hoge.h>
 EOF
 
+cat <<'EOF' > expected
+42
+EOF
+
+test_exit_code 0 <<'EOF'
+#ifdef FOO
+#include FOO
+#endif
+
+int main() { 1 < 2; }
+EOF
-- 
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