Add specs for reserved keywords

language/reserved_keywords.rb

@@ -0,0 +1,155 @@
+require_relative '../spec_helper'
+
+describe "Ruby's reserved keywords" do
+  # Copied from Prism::Translation::Ripper
+  keywords = [
+    "alias",
+    "and",
+    "begin",
+    "BEGIN",
+    "break",
+    "case",
+    "class",
+    "def",
+    "defined?",
+    "do",
+    "else",
+    "elsif",
+    "end",
+    "END",
+    "ensure",
+    "false",
+    "for",
+    "if",
+    "in",
+    "module",
+    "next",
+    "nil",
+    "not",
+    "or",
+    "redo",
+    "rescue",
+    "retry",
+    "return",
+    "self",
+    "super",
+    "then",
+    "true",
+    "undef",
+    "unless",
+    "until",
+    "when",
+    "while",
+    "yield",
+    "__ENCODING__",
+    "__FILE__",
+    "__LINE__"
+  ]
+
+  keywords.each do |kw|
+    describe "keyword '#{kw}'" do
+      it "can't be used as local variable name" do
+        expect_syntax_error <<~RUBY
+            #{kw} = "a local variable named '#{kw}'"
+        RUBY
+      end
+
+      invalid_ivar_names = ["defined?"]
+
+      if invalid_ivar_names.include?(kw)
+        it "can't be used as an instance variable name" do
+          expect_syntax_error <<~RUBY
+            @#{kw} = "an instance variable named '#{kw}'"
+          RUBY
+        end
+      else
+        it "can be used as an instance variable name" do
+          result = sandboxed_eval <<~RUBY
+            @#{kw} = "an instance variable named '#{kw}'"
+            @#{kw}
+          RUBY
+
+          result.should == "an instance variable named '#{kw}'"
+        end
+      end
+
+      invalid_class_var_names = ["defined?"]
+
+      if invalid_class_var_names.include?(kw)
+        it "can't be used as a global variable name" do
+          expect_syntax_error <<~RUBY
+            @@#{kw} = "a class variable named '#{kw}'"
+          RUBY
+        end
+      else
+        it "can be used as a class variable name" do
+          result = sandboxed_eval <<~RUBY
+            @@#{kw} = "a class variable named '#{kw}'"
+            @@#{kw}
+          RUBY
+
+          result.should == "a class variable named '#{kw}'"
+        end
+      end
+
+      invalid_global_var_names = ["defined?"]
+
+      if invalid_global_var_names.include?(kw)
+        it "can't be used as a global variable name" do
+          expect_syntax_error <<~RUBY
+            $#{kw} = "a global variable named '#{kw}'"
+          RUBY
+        end
+      else
+        it "can be used as a global variable name" do
+          result = sandboxed_eval <<~RUBY
+            $#{kw} = "a global variable named '#{kw}'"
+            $#{kw}
+          RUBY
+
+          result.should == "a global variable named '#{kw}'"
+        end
+      end
+
+      it "can't be used as a positional parameter name" do
+        expect_syntax_error <<~RUBY
+          def x(#{kw}); end
+        RUBY
+      end
+
+      invalid_kw_param_names = ["BEGIN","END","defined?"]
+
+      if invalid_kw_param_names.include?(kw)
+        it "can't be used a keyword parameter name" do
+          expect_syntax_error <<~RUBY
+            def m(#{kw}:); end
+          RUBY
+        end
+      else
+        it "can be used a keyword parameter name" do
+          result = sandboxed_eval <<~RUBY
+            def m(#{kw}:)
+              binding.local_variable_get(:#{kw})
+            end
+
+            m(#{kw}: "an argument to '#{kw}'")
+          RUBY
+
+          result.should == "an argument to '#{kw}'"
+        end
+      end
+
+      it "can be used as a method name" do
+        result = sandboxed_eval <<~RUBY
+          def #{kw}
+            "a method named '#{kw}'"
+          end
+
+          send(:#{kw})
+        RUBY
+
+        result.should == "a method named '#{kw}'"
+      end
+    end
+  end
+end

spec_helper.rb

@@ -40,3 +40,13 @@ def report_on_exception=(value)
 def expect_syntax_error(ruby_src)
   -> { eval(ruby_src) }.should raise_error(SyntaxError)
 end
+
+# Evaluates the given Ruby source in a temporary Module, to prevent
+# the surrounding context from being polluted with the new methods.
+def sandboxed_eval(ruby_src)
+  Module.new do
+    # Allows instance methods defined by `ruby_src` to be called directly.
+    extend self
+  end
+  .class_eval(ruby_src)
+end