Turn class variable warnings into exceptions

This changes the following warnings:

* warning: class variable access from toplevel
* warning: class variable @foo of D is overtaken by C

into RuntimeErrors.  Handle defined?(@@foo) at toplevel
by returning nil instead of raising an exception (the previous
behavior warned before returning nil when defined? was used).

Refactor the specs to avoid the warnings even in older versions.
The specs were checking for the warnings, but the purpose of
the related specs as evidenced from their description is to
test for behavior, not for warnings.

Fixes [Bug #14541]

bootstraptest/test_eval.rb

@@ -250,7 +250,9 @@ assert_equal 'ok', %q{
 
 assert_equal 'ok', %q{
   begin
-    12.instance_eval { @@a }
+    class A
+      12.instance_eval { @@a }
+    end
   rescue NameError
     :ok
   end
@@ -258,7 +260,9 @@ assert_equal 'ok', %q{
 
 assert_equal 'ok', %q{
   begin
-    12.instance_exec { @@a }
+    class A
+      12.instance_exec { @@a }
+    end
   rescue NameError
     :ok
   end

bootstraptest/test_insns.rb

@@ -64,8 +64,8 @@ tests = [
   [ 'setinstancevariable', %q{ @x = true }, ],
   [ 'getinstancevariable', %q{ @x = true; @x }, ],
 
-  [ 'setclassvariable', %q{ @@x = true }, ],
-  [ 'getclassvariable', %q{ @@x = true; @@x }, ],
+  [ 'setclassvariable', %q{ class A; @@x = true; end }, ],
+  [ 'getclassvariable', %q{ class A; @@x = true; @@x end }, ],
 
   [ 'setconstant', %q{ X = true }, ],
   [ 'setconstant', %q{ Object::X = true }, ],

bootstraptest/test_syntax.rb

@@ -268,8 +268,10 @@ assert_equal %q{}, %q{
   defined?(@@a)
 }
 assert_equal %q{class variable}, %q{
-  @@a = 1
-  defined?(@@a)
+  class A
+    @@a = 1
+    defined?(@@a)
+  end
 }
 assert_equal %q{}, %q{
   defined?($a)

insns.def

@@ -236,7 +236,7 @@ getclassvariable
 /* "class variable access from toplevel" warning can be hooked. */
 // attr bool leaf = false; /* has rb_warning() */
 {
-    val = rb_cvar_get(vm_get_cvar_base(vm_get_cref(GET_EP()), GET_CFP()), id);
+    val = rb_cvar_get(vm_get_cvar_base(vm_get_cref(GET_EP()), GET_CFP(), 1), id);
 }
 
 /* Set value of class variable id of klass as val. */
@@ -249,7 +249,7 @@ setclassvariable
 // attr bool leaf = false; /* has rb_warning() */
 {
     vm_ensure_not_refinement_module(GET_SELF());
-    rb_cvar_set(vm_get_cvar_base(vm_get_cref(GET_EP()), GET_CFP()), id, val);
+    rb_cvar_set(vm_get_cvar_base(vm_get_cref(GET_EP()), GET_CFP(), 1), id, val);
 }
 
 /* Get constant variable id. If klass is Qnil and allow_nil is Qtrue, constants

spec/ruby/core/exception/name_spec.rb

@@ -21,9 +21,7 @@ describe "NameError#name" do
 
   it "returns a class variable name as a symbol" do
     -> {
-      -> {
-        @@doesnt_exist
-      }.should complain(/class variable access from toplevel/)
+      eval("class singleton_class::A; @@doesnt_exist end", binding, __FILE__, __LINE__)
     }.should raise_error(NameError) { |e| e.name.should == :@@doesnt_exist }
   end
 

spec/ruby/core/exception/receiver_spec.rb

@@ -28,10 +28,8 @@ describe "NameError#receiver" do
 
   it "returns the Object class when an undefined class variable is called" do
     -> {
-      -> {
-        @@doesnt_exist
-      }.should complain(/class variable access from toplevel/)
-    }.should raise_error(NameError) {|e| e.receiver.should equal(Object) }
+      eval("class singleton_class::A; @@doesnt_exist end", binding, __FILE__, __LINE__)
+    }.should raise_error(NameError) {|e| e.receiver.should equal(singleton_class::A) }
   end
 
   it "returns a class when an undefined class variable is called in a subclass' namespace" do

spec/ruby/language/defined_spec.rb

@@ -275,9 +275,7 @@ describe "The defined? keyword for an expression" do
     end
 
     it "returns nil for an expression with '!' and an unset class variable" do
-      -> {
-        @result = defined?(!@@defined_specs_undefined_class_variable)
-      }.should complain(/class variable access from toplevel/)
+      @result = eval("class singleton_class::A; defined?(!@@doesnt_exist) end", binding, __FILE__, __LINE__)
       @result.should be_nil
     end
 
@@ -286,9 +284,7 @@ describe "The defined? keyword for an expression" do
     end
 
     it "returns nil for an expression with 'not' and an unset class variable" do
-      -> {
-        @result = defined?(not @@defined_specs_undefined_class_variable)
-      }.should complain(/class variable access from toplevel/)
+      @result = eval("class singleton_class::A; defined?(not @@doesnt_exist) end", binding, __FILE__, __LINE__)
       @result.should be_nil
     end
 
@@ -897,17 +893,21 @@ describe "The defined? keyword for a variable scoped constant" do
   end
 
   it "returns nil if the class scoped constant is not defined" do
-    -> {
-      @@defined_specs_obj = DefinedSpecs::Basic
-      defined?(@@defined_specs_obj::Undefined).should be_nil
-    }.should complain(/class variable access from toplevel/)
+    eval(<<-END, binding, __FILE__, __LINE__)
+      class singleton_class::A
+        @@defined_specs_obj = DefinedSpecs::Basic
+        defined?(@@defined_specs_obj::Undefined).should be_nil
+      end
+    END
   end
 
   it "returns 'constant' if the constant is defined in the scope of the class variable" do
-    -> {
-      @@defined_specs_obj = DefinedSpecs::Basic
-      defined?(@@defined_specs_obj::A).should == "constant"
-    }.should complain(/class variable access from toplevel/)
+    eval(<<-END, binding, __FILE__, __LINE__)
+      class singleton_class::A
+        @@defined_specs_obj = DefinedSpecs::Basic
+        defined?(@@defined_specs_obj::A).should == "constant"
+      end
+    END
   end
 
   it "returns nil if the local scoped constant is not defined" do

variable.c

@@ -3064,7 +3064,8 @@ cvar_overtaken(VALUE front, VALUE target, ID id)
 	st_data_t did = (st_data_t)id;
 
         if (RTEST(ruby_verbose) && original_module(front) != original_module(target)) {
-	    rb_warning("class variable % "PRIsVALUE" of %"PRIsVALUE" is overtaken by %"PRIsVALUE"",
+            rb_raise(rb_eRuntimeError,
+                     "class variable % "PRIsVALUE" of %"PRIsVALUE" is overtaken by %"PRIsVALUE"",
 		       ID2SYM(id), rb_class_name(original_module(front)),
 		       rb_class_name(original_module(target)));
 	}

vm_insnhelper.c

@@ -989,7 +989,7 @@ vm_get_ev_const(rb_execution_context_t *ec, VALUE orig_klass, ID id, bool allow_
 }
 
 static inline VALUE
-vm_get_cvar_base(const rb_cref_t *cref, rb_control_frame_t *cfp)
+vm_get_cvar_base(const rb_cref_t *cref, rb_control_frame_t *cfp, int top_level_raise)
 {
     VALUE klass;
 
@@ -1002,8 +1002,8 @@ vm_get_cvar_base(const rb_cref_t *cref, rb_control_frame_t *cfp)
 	    CREF_PUSHED_BY_EVAL(cref))) {
 	cref = CREF_NEXT(cref);
     }
-    if (!CREF_NEXT(cref)) {
-	rb_warn("class variable access from toplevel");
+    if (top_level_raise && !CREF_NEXT(cref)) {
+        rb_raise(rb_eRuntimeError, "class variable access from toplevel");
     }
 
     klass = vm_get_iclass(cfp, CREF_CLASS(cref));
@@ -3567,7 +3567,7 @@ vm_defined(rb_execution_context_t *ec, rb_control_frame_t *reg_cfp, rb_num_t op_
 	break;
       case DEFINED_CVAR: {
         const rb_cref_t *cref = vm_get_cref(GET_EP());
-	klass = vm_get_cvar_base(cref, GET_CFP());
+        klass = vm_get_cvar_base(cref, GET_CFP(), 0);
 	if (rb_cvar_defined(klass, SYM2ID(obj))) {
 	    expr_type = DEFINED_CVAR;
 	}