From 0667d23f4f083ca56906a2f1695a60bf4779618a Mon Sep 17 00:00:00 2001
From: Earlopain <14981592+Earlopain@users.noreply.github.com>
Date: Thu, 26 Mar 2026 19:08:45 +0100
Subject: [PATCH] Fix `Source.offsets` with `freeze: true`

We still need to do it eagerly when the result will be frozen, same
as for locations.

Fixes the following error for the added test:
> FrozenError: can't modify frozen Prism::ASCIISource: #<Prism::ASCIISource:0x00007ff9d57586f0 @source="1 + 2", @start_line=1, @offsets="\x00\x00\x00\x00">
---
 templates/ext/prism/api_node.c.erb | 9 ++++++++-
 test/prism/api/freeze_test.rb      | 5 +++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/templates/ext/prism/api_node.c.erb b/templates/ext/prism/api_node.c.erb
index 71f7fe273e..41d7165930 100644
--- a/templates/ext/prism/api_node.c.erb
+++ b/templates/ext/prism/api_node.c.erb
@@ -82,11 +82,18 @@ pm_source_new(const pm_parser_t *parser, rb_encoding *encoding, bool freeze) {
     VALUE source_string = rb_enc_str_new((const char *) start, pm_parser_end(parser) - start, encoding);
 
     const pm_line_offset_list_t *line_offsets = pm_parser_line_offsets(parser);
-    VALUE offsets = rb_str_new((const char *) line_offsets->offsets, line_offsets->size * sizeof(uint32_t));
+    VALUE offsets;
 
     if (freeze) {
+        offsets = rb_ary_new_capa(line_offsets->size);
+        for (size_t index = 0; index < line_offsets->size; index++) {
+            rb_ary_push(offsets, ULONG2NUM(line_offsets->offsets[index]));
+        }
+
         rb_obj_freeze(source_string);
         rb_obj_freeze(offsets);
+    } else {
+        offsets = rb_str_new((const char *) line_offsets->offsets, line_offsets->size * sizeof(uint32_t));
     }
 
     VALUE source = rb_funcall(rb_cPrismSource, rb_intern("for"), 3, source_string, LONG2NUM(pm_parser_start_line(parser)), offsets);
diff --git a/test/prism/api/freeze_test.rb b/test/prism/api/freeze_test.rb
index 5533a00331..bf91792e69 100644
--- a/test/prism/api/freeze_test.rb
+++ b/test/prism/api/freeze_test.rb
@@ -8,6 +8,11 @@ def test_parse
       assert_frozen(Prism.parse("1 + 2; %i{foo} + %i{bar}", freeze: true))
     end
 
+    def test_offsets_usable
+      node = Prism.parse_statement("1 + 2", freeze: true)
+      assert_equal(1, node.start_line)
+    end
+
     def test_lex
       assert_frozen(Prism.lex("1 + 2; %i{foo} + %i{bar}", freeze: true))
     end