https://git.ruby-lang.org/ruby.git/commit/?id=3754e15530

From 3754e155309ed430250781c616a6e52b54ef511d Mon Sep 17 00:00:00 2001
From: Nobuyoshi Nakada <nobu@r...>
Date: Thu, 29 Aug 2019 22:07:45 +0900
Subject: Warn local variables which conflict with new numbered parameters


diff --git a/defs/id.def b/defs/id.def
index 9b3fb00..6bfce29 100644
--- a/defs/id.def
+++ b/defs/id.def
@@ -57,6 +57,19 @@ firstline, predefined = __LINE__+1, %[\ https://github.com/ruby/ruby/blob/trunk/defs/id.def#L57
   nil
 
   _                                                     UScore
+
+  # MUST be successive
+  _0  NUMPARAM_0
+  _1  NUMPARAM_1
+  _2  NUMPARAM_2
+  _3  NUMPARAM_3
+  _4  NUMPARAM_4
+  _5  NUMPARAM_5
+  _6  NUMPARAM_6
+  _7  NUMPARAM_7
+  _8  NUMPARAM_8
+  _9  NUMPARAM_9
+
   "/*NULL*/"                                            NULL
   empty?
   eql?
diff --git a/parse.y b/parse.y
index 63d8f53..602c572 100644
--- a/parse.y
+++ b/parse.y
@@ -11652,6 +11652,10 @@ arg_var(struct parser_params *p, ID id) https://github.com/ruby/ruby/blob/trunk/parse.y#L11652
 static void
 local_var(struct parser_params *p, ID id)
 {
+    if (id >= idNUMPARAM_0 && id <= idNUMPARAM_9) {
+	rb_warn1("`_%d' is used as numbered parameter",
+		 WARN_I((int)(id - idNUMPARAM_0)));
+    }
     vtable_add(p->lvtbl->vars, id);
     if (p->lvtbl->used) {
 	vtable_add(p->lvtbl->used, (ID)p->ruby_sourceline);
-- 
cgit v0.10.2


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