From d40ec25228e581ada37957c1dc3bb894bc642366 Mon Sep 17 00:00:00 2001
From: Jeremy Evans <code@jeremyevans.net>
Date: Tue, 9 Aug 2016 08:33:14 -0700
Subject: [PATCH] Add Warning module for customized warning handling

This makes all warnings raised call Warning.warn, which by default
does the same thing it does currently (rb_write_error_str).  You can
override Warning.warn to change the behavior.
---
 error.c                     | 37 +++++++++++++++++++++++++++++--------
 test/ruby/test_exception.rb | 27 +++++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 8 deletions(-)

diff --git a/error.c b/error.c
index 27ca7db..198e399 100644
--- a/error.c
+++ b/error.c
@@ -42,6 +42,9 @@ VALUE rb_iseqw_new(const rb_iseq_t *);
 VALUE rb_eEAGAIN;
 VALUE rb_eEWOULDBLOCK;
 VALUE rb_eEINPROGRESS;
+VALUE rb_mWarning;
+
+static ID id_warn;
 
 extern const char ruby_description[];
 
@@ -147,6 +150,19 @@ ruby_only_for_internal_use(const char *func)
 }
 
 static VALUE
+rb_warning_s_warn(VALUE mod, VALUE str)
+{
+    rb_write_error_str(str);
+    return Qnil;
+}
+
+static void
+rb_write_warning_str(VALUE str)
+{
+    rb_funcall(rb_mWarning, id_warn, 1, str);
+}
+
+static VALUE
 warn_vsprintf(rb_encoding *enc, const char *file, int line, const char *fmt, va_list args)
 {
     VALUE str = rb_enc_str_new(0, 0, enc);
@@ -166,7 +182,7 @@ rb_compile_warn(const char *file, int line, const char *fmt, ...)
     va_start(args, fmt);
     str = warn_vsprintf(NULL, file, line, fmt, args);
     va_end(args);
-    rb_write_error_str(str);
+    rb_write_warning_str(str);
 }
 
 /* rb_compile_warning() reports only in verbose mode */
@@ -181,7 +197,7 @@ rb_compile_warning(const char *file, int line, const char *fmt, ...)
     va_start(args, fmt);
     str = warn_vsprintf(NULL, file, line, fmt, args);
     va_end(args);
-    rb_write_error_str(str);
+    rb_write_warning_str(str);
 }
 
 static VALUE
@@ -206,7 +222,7 @@ rb_warn(const char *fmt, ...)
     va_start(args, fmt);
     mesg = warning_string(0, fmt, args);
     va_end(args);
-    rb_write_error_str(mesg);
+    rb_write_warning_str(mesg);
 }
 
 void
@@ -220,7 +236,7 @@ rb_enc_warn(rb_encoding *enc, const char *fmt, ...)
     va_start(args, fmt);
     mesg = warning_string(enc, fmt, args);
     va_end(args);
-    rb_write_error_str(mesg);
+    rb_write_warning_str(mesg);
 }
 
 /* rb_warning() reports only in verbose mode */
@@ -235,7 +251,7 @@ rb_warning(const char *fmt, ...)
     va_start(args, fmt);
     mesg = warning_string(0, fmt, args);
     va_end(args);
-    rb_write_error_str(mesg);
+    rb_write_warning_str(mesg);
 }
 
 #if 0
@@ -250,7 +266,7 @@ rb_enc_warning(rb_encoding *enc, const char *fmt, ...)
     va_start(args, fmt);
     mesg = warning_string(enc, fmt, args);
     va_end(args);
-    rb_write_error_str(mesg);
+    rb_write_warning_str(mesg);
 }
 #endif
 
@@ -2052,6 +2068,10 @@ Init_Exception(void)
 
     rb_mErrno = rb_define_module("Errno");
 
+    rb_mWarning = rb_define_module("Warning");
+    rb_define_method(rb_mWarning, "warn", rb_warning_s_warn, 1);
+    rb_extend_object(rb_mWarning, rb_mWarning);
+
     rb_define_global_function("warn", rb_warn_m, -1);
 
     id_new = rb_intern_const("new");
@@ -2066,6 +2086,7 @@ Init_Exception(void)
     id_Errno = rb_intern_const("Errno");
     id_errno = rb_intern_const("errno");
     id_i_path = rb_intern_const("@path");
+    id_warn = rb_intern_const("warn");
     id_iseq = rb_make_internal_id();
 }
 
@@ -2289,7 +2310,7 @@ rb_sys_warning(const char *fmt, ...)
     va_end(args);
     rb_str_set_len(mesg, RSTRING_LEN(mesg)-1);
     rb_str_catf(mesg, ": %s\n", strerror(errno_save));
-    rb_write_error_str(mesg);
+    rb_write_warning_str(mesg);
     errno = errno_save;
 }
 
@@ -2309,7 +2330,7 @@ rb_sys_enc_warning(rb_encoding *enc, const char *fmt, ...)
     va_end(args);
     rb_str_set_len(mesg, RSTRING_LEN(mesg)-1);
     rb_str_catf(mesg, ": %s\n", strerror(errno_save));
-    rb_write_error_str(mesg);
+    rb_write_warning_str(mesg);
     errno = errno_save;
 }
 
diff --git a/test/ruby/test_exception.rb b/test/ruby/test_exception.rb
index 5023262..3107b61 100644
--- a/test/ruby/test_exception.rb
+++ b/test/ruby/test_exception.rb
@@ -855,4 +855,31 @@ def test_message_of_name_error
       end
     end
   end
+
+  def test_warning_warn
+    verbose = $VERBOSE
+    warning = nil
+
+    ::Warning.class_eval do
+      alias_method :warn2, :warn
+      remove_method :warn
+
+      define_method(:warn) do |str|
+        warning = str
+      end
+    end
+
+    $VERBOSE = true
+    a = @a
+
+    assert_match(/instance variable @a not initialized/, warning)
+  ensure
+    $VERBOSE = verbose
+
+    ::Warning.class_eval do
+      remove_method :warn
+      alias_method :warn, :warn2
+      remove_method :warn2
+    end
+  end
 end
-- 
2.9.0