New rule: variable names

spec/ameba/rules/variable_names_spec.cr

@@ -0,0 +1,61 @@
+require "../../spec_helper"
+
+module Ameba
+  subject = Rules::VariableNames.new
+
+  private def it_reports_var_name(content, expected)
+    it "reports method name #{expected}" do
+      s = Source.new content
+      Rules::VariableNames.new.catch(s).should_not be_valid
+      s.errors.first.message.should contain expected
+    end
+  end
+
+  describe Rules::VariableNames do
+    it "passes if var names are underscore-cased" do
+      s = Source.new %(
+        class Greeting
+          @@default_greeting = "Hello world"
+
+          def initialize(@custom_greeting = nil)
+          end
+
+          def print_greeting
+            greeting = @custom_greeting || @@default_greeting
+            puts greeting
+          end
+        end
+      )
+      subject.catch(s).should be_valid
+    end
+
+    it_reports_var_name %(myBadNamedVar = 1), "my_bad_named_var"
+    it_reports_var_name %(wrong_Name = 'y'), "wrong_name"
+
+    it_reports_var_name %(
+      class Greeting
+        def initialize(@badNamed = nil)
+        end
+      end
+    ), "bad_named"
+
+    it_reports_var_name %(
+      class Greeting
+        @@defaultGreeting = "Hello world"
+      end
+    ), "default_greeting"
+
+    it "reports rule, pos and message" do
+      s = Source.new %(
+        badName = "Yeah"
+      )
+      subject.catch(s).should_not be_valid
+      error = s.errors.first
+      error.rule.should_not be_nil
+      error.pos.should eq 2
+      error.message.should eq(
+        "Var name should be underscore-cased: bad_name, not badName"
+      )
+    end
+  end
+end

src/ameba/ast/traverse.cr

@@ -6,13 +6,16 @@ module Ameba::AST
     Call,
     Case,
     ClassDef,
+    ClassVar,
     Def,
     EnumDef,
     If,
+    InstanceVar,
     LibDef,
     ModuleDef,
     StringInterpolation,
     Unless,
+    Var,
   ]
 
   abstract class Visitor < Crystal::Visitor

src/ameba/rules/variable_names.cr

@@ -0,0 +1,55 @@
+module Ameba::Rules
+  # A rule that enforces variable names to be in underscored case.
+  #
+  # For example, these variable names are considered valid:
+  #
+  # ```
+  # class Greeting
+  #   @@default_greeting = "Hello world"
+  #
+  #   def initialize(@custom_greeting = nil)
+  #   end
+  #
+  #   def print_greeting
+  #     greeting = @custom_greeting || @@default_greeting
+  #     puts greeting
+  #   end
+  # end
+  # ```
+  #
+  # And these are invalid method names:
+  #
+  # ```
+  # myBadNamedVar = 1
+  # wrong_Name = 2
+  # ```
+  #
+  struct VariableNames < Rule
+    def test(source)
+      [
+        AST::VarVisitor,
+        AST::InstanceVarVisitor,
+        AST::ClassVarVisitor,
+      ].each &.new(self, source)
+    end
+
+    private def check_node(source, node)
+      return if (expected = node.name.underscore) == node.name
+
+      source.error self, node.location.try &.line_number,
+        "Var name should be underscore-cased: #{expected}, not #{node.name}"
+    end
+
+    def test(source, node : Crystal::Var)
+      check_node source, node
+    end
+
+    def test(source, node : Crystal::InstanceVar)
+      check_node source, node
+    end
+
+    def test(source, node : Crystal::ClassVar)
+      check_node source, node
+    end
+  end
+end