For prism parser, do not update $_ from STDIN

Fixes [Bug #21635]

2 files changed, 11 insertions, 3 deletions

diff --git a/io.c b/io.c
index caa364a70b..d412d14963 100644
--- a/io.c
+++ b/io.c
@@ -4307,11 +4307,17 @@ rb_io_gets(VALUE io)
 }
 
 VALUE
-rb_io_gets_internal(VALUE io)
+rb_io_gets_limit_internal(VALUE io, long limit)
 {
     rb_io_t *fptr;
     GetOpenFile(io, fptr);
-    return rb_io_getline_0(rb_default_rs, -1, FALSE, fptr);
+    return rb_io_getline_0(rb_default_rs, limit, FALSE, fptr);
+}
+
+VALUE
+rb_io_gets_internal(VALUE io)
+{
+    return rb_io_gets_limit_internal(io, -1);
 }
 
 /*
diff --git a/prism_compile.c b/prism_compile.c
index 66bee579c9..86753c90cc 100644
--- a/prism_compile.c
+++ b/prism_compile.c
@@ -11466,6 +11466,8 @@ pm_parse_stdin_eof(void *stream)
     return wrapped_stdin->eof_seen;
 }
 
+VALUE rb_io_gets_limit_internal(VALUE io, long limit);
+
 /**
  * An implementation of fgets that is suitable for use with Ruby IO objects.
  */
@@ -11476,7 +11478,7 @@ pm_parse_stdin_fgets(char *string, int size, void *stream)
 
     struct rb_stdin_wrapper * wrapped_stdin = (struct rb_stdin_wrapper *)stream;
 
-    VALUE line = rb_funcall(wrapped_stdin->rb_stdin, rb_intern("gets"), 1, INT2FIX(size - 1));
+    VALUE line = rb_io_gets_limit_internal(wrapped_stdin->rb_stdin, size - 1);
     if (NIL_P(line)) {
         return NULL;
     }