From 3d3bc029c5b48ddfbb7c5f7b062cb364894c64af Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@ruby-lang.org>
Date: Thu, 11 Jan 2024 18:46:51 +0900
Subject: [PATCH] Reject encodings determined at runtime as source code
 encodings

The encodings determined at runtime are affected by the runtime
environment, such as the OS and locale, while the file contents are
not.
---
 parse.y                 | 11 ++++++++++-
 test/ruby/test_parse.rb | 28 ++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/parse.y b/parse.y
index 8eef24ebba..08bd3fb97d 100644
--- a/parse.y
+++ b/parse.y
@@ -9477,11 +9477,20 @@ parser_encode_length(struct parser_params *p, const char *name, long len)
 static void
 parser_set_encode(struct parser_params *p, const char *name)
 {
-    int idx = rb_enc_find_index(name);
     rb_encoding *enc;
     VALUE excargs[3];
 
+    const char *wrong = 0;
+    switch (*name) {
+      case 'e': case 'E': wrong = "external"; break;
+      case 'i': case 'I': wrong = "internal"; break;
+      case 'f': case 'F': wrong = "filesystem"; break;
+      case 'l': case 'L': wrong = "locale"; break;
+    }
+    if (wrong && STRCASECMP(name, wrong) == 0) goto unknown;
+    int idx = rb_enc_find_index(name);
     if (idx < 0) {
+      unknown:
         excargs[1] = rb_sprintf("unknown encoding name: %s", name);
       error:
         excargs[0] = rb_eArgError;
diff --git a/test/ruby/test_parse.rb b/test/ruby/test_parse.rb
index c2f02ff809..858c623bcc 100644
--- a/test/ruby/test_parse.rb
+++ b/test/ruby/test_parse.rb
@@ -767,6 +767,34 @@ x = __ENCODING__
       END
     end
     assert_equal(__ENCODING__, x)
+
+    assert_raise(ArgumentError) do
+      EnvUtil.with_default_external(Encoding::US_ASCII) {eval <<-END, nil, __FILE__, __LINE__+1}
+# coding = external
+x = __ENCODING__
+      END
+    end
+
+    assert_raise(ArgumentError) do
+      EnvUtil.with_default_internal(Encoding::US_ASCII) {eval <<-END, nil, __FILE__, __LINE__+1}
+# coding = internal
+x = __ENCODING__
+      END
+    end
+
+    assert_raise(ArgumentError) do
+      eval <<-END, nil, __FILE__, __LINE__+1
+# coding = filesystem
+x = __ENCODING__
+      END
+    end
+
+    assert_raise(ArgumentError) do
+      eval <<-END, nil, __FILE__, __LINE__+1
+# coding = locale
+x = __ENCODING__
+      END
+    end
   end
 
   def test_utf8_bom