New rule: RedundantWithObject (#121)

spec/ameba/rule/lint/redundant_with_object_spec.cr

@@ -0,0 +1,83 @@
+require "../../../spec_helper"
+
+module Ameba::Rule::Lint
+  describe RedundantWithObject do
+    subject = RedundantWithObject.new
+
+    it "does not report if there is index argument" do
+      s = Source.new %(
+        collection.each_with_object(0) do |e, obj|
+          obj += i
+        end
+      )
+      subject.catch(s).should be_valid
+    end
+
+    it "reports if there is not index argument" do
+      s = Source.new %(
+        collection.each_with_object(0) do |e|
+          e += 1
+        end
+      )
+      subject.catch(s).should_not be_valid
+    end
+
+    it "reports if there is underscored index argument" do
+      s = Source.new %(
+        collection.each_with_object(0) do |e, _|
+          e += 1
+        end
+      )
+      subject.catch(s).should_not be_valid
+    end
+
+    it "reports if there is no args" do
+      s = Source.new %(
+        collection.each_with_object(0) do
+          puts :nothing
+        end
+      )
+      subject.catch(s).should_not be_valid
+    end
+
+    it "does not report if there is no block" do
+      s = Source.new %(
+        collection.each_with_object(0)
+      )
+      subject.catch(s).should be_valid
+    end
+
+    it "does not report if first argument is underscored" do
+      s = Source.new %(
+        collection.each_with_object(0) do |_, obj|
+          puts i
+        end
+      )
+      subject.catch(s).should be_valid
+    end
+
+    it "does not report if there are more than 2 args" do
+      s = Source.new %(
+        tup.each_with_object(0) do |key, value, obj|
+          puts i
+        end
+      )
+      subject.catch(s).should be_valid
+    end
+
+    it "reports rule, location and message" do
+      s = Source.new %(
+        def valid?
+          collection.each_with_object(0) do |e|
+          end
+        end
+      ), "source.cr"
+      subject.catch(s).should_not be_valid
+      issue = s.issues.first
+      issue.rule.should_not be_nil
+      issue.location.to_s.should eq "source.cr:2:14"
+      issue.end_location.to_s.should eq "source.cr:2:30"
+      issue.message.should eq "Use each instead of each_with_object"
+    end
+  end
+end

src/ameba/rule/lint/redundant_with_object.cr

@@ -0,0 +1,55 @@
+module Ameba::Rule::Lint
+  # A rule that disallows redundant `each_with_object` calls.
+  #
+  # For example, this is considered invalid:
+  #
+  # ```
+  # collection.each_with_object(0) do |e|
+  #   # ...
+  # end
+  #
+  # collection.each_with_object(0) do |e, _|
+  #   # ...
+  # end
+  # ```
+  #
+  # and it should be written as follows:
+  #
+  # ```
+  # collection.each do |e|
+  #   # ...
+  # end
+  # ```
+  #
+  # YAML configuration example:
+  #
+  # ```
+  # Lint/RedundantWithObject:
+  #   Enabled: true
+  # ```
+  #
+  struct RedundantWithObject < Base
+    properties do
+      description "Disallows redundant `with_object` calls"
+    end
+
+    def test(source)
+      AST::NodeVisitor.new self, source
+    end
+
+    def test(source, node : Crystal::Call)
+      return if node.name != "each_with_object" ||
+                node.args.size != 1 ||
+                node.block.nil? ||
+                with_index_arg?(node.block.not_nil!)
+
+      issue_for node.name_location,
+        node.name_end_location,
+        "Use each instead of each_with_object"
+    end
+
+    private def with_index_arg?(block : Crystal::Block)
+      block.args.size >= 2 && block.args.last.name != "_"
+    end
+  end
+end