From 8a6746b54440128d17d27727310dbe81586ef607 Mon Sep 17 00:00:00 2001
From: Kevin Newton <kddnewton@gmail.com>
Date: Thu, 3 Sep 2026 15:31:36 -0400
Subject: [PATCH] Check heredoc state for escaped newlines

When escaped newlines are encountered, they are added to the newline
list. We need to check that we aren't backing up to read the rest of
the line because of a heredoc, in which case the newline would have
already have been added to the list.
---
 src/prism.c               | 10 +++++-----
 test/prism/fuzzer_test.rb |  4 ++++
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/src/prism.c b/src/prism.c
index ecb329bef6..8754aecc9b 100644
--- a/src/prism.c
+++ b/src/prism.c
@@ -9064,7 +9064,7 @@ escape_write_escape_encoded(pm_parser_t *parser, pm_buffer_t *buffer, pm_buffer_
     }
 
     if (width == 1) {
-        if (*parser->current.end == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
+        if (parser->heredoc_end == NULL && *parser->current.end == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
         escape_write_byte(parser, buffer, regular_expression_buffer, flags, escape_byte(*parser->current.end++, flags));
     } else if (width > 1) {
         // Valid multibyte character.  Just ignore escape.
@@ -9381,7 +9381,7 @@ escape_read(pm_parser_t *parser, pm_buffer_t *buffer, pm_buffer_t *regular_expre
                         return;
                     }
 
-                    if (peeked == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
+                    if (parser->heredoc_end == NULL && peeked == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
                     parser->current.end++;
                     escape_write_byte(parser, buffer, regular_expression_buffer, flags, escape_byte(peeked, flags | PM_ESCAPE_FLAG_CONTROL));
                     return;
@@ -9440,7 +9440,7 @@ escape_read(pm_parser_t *parser, pm_buffer_t *buffer, pm_buffer_t *regular_expre
                         return;
                     }
 
-                    if (peeked == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
+                    if (parser->heredoc_end == NULL && peeked == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
                     parser->current.end++;
                     escape_write_byte(parser, buffer, regular_expression_buffer, flags, escape_byte(peeked, flags | PM_ESCAPE_FLAG_CONTROL));
                     return;
@@ -9494,7 +9494,7 @@ escape_read(pm_parser_t *parser, pm_buffer_t *buffer, pm_buffer_t *regular_expre
                         return;
                     }
 
-                    if (peeked == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
+                    if (parser->heredoc_end == NULL && peeked == '\n') pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 1);
                     parser->current.end++;
                     escape_write_byte(parser, buffer, regular_expression_buffer, flags, escape_byte(peeked, flags | PM_ESCAPE_FLAG_META));
                     return;
@@ -9502,7 +9502,7 @@ escape_read(pm_parser_t *parser, pm_buffer_t *buffer, pm_buffer_t *regular_expre
         }
         case '\r': {
             if (peek_offset(parser, 1) == '\n') {
-                pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 2);
+                if (parser->heredoc_end == NULL) pm_line_offset_list_append(&parser->metadata_arena, &parser->line_offsets, PM_TOKEN_END(parser, &parser->current) + 2);
                 parser->current.end += 2;
                 escape_write_byte_encoded(parser, buffer, flags, escape_byte('\n', flags));
                 return;
diff --git a/test/prism/fuzzer_test.rb b/test/prism/fuzzer_test.rb
index 4927478bdc..b6a18ab51e 100644
--- a/test/prism/fuzzer_test.rb
+++ b/test/prism/fuzzer_test.rb
@@ -63,5 +63,9 @@ def self.snippet(name, source)
       a
       /{/, ''\\
     RUBY
+
+    snippet "escaped newline in char literal after heredoc opener", "<<i=?\\\n\n\n"
+    snippet "escaped newline in char literal after heredoc opener with operator", "<<T^?\\\n\n\n"
+    snippet "control escape consuming newline after heredoc in interpolation", "%\n\#{<<e}\\c\n\n"
   end
 end