New rule: debugger statement

spec/ameba/rules/debugger_statement_spec.cr

@@ -0,0 +1,44 @@
+require "../../spec_helper"
+
+module Ameba::Rules
+  subject = DebuggerStatement.new
+
+  describe DebuggerStatement do
+    it "passes if there is no debugger statement" do
+      s = Source.new %(
+        "this is not a debugger statement"
+        s = "debugger"
+
+        def debugger(program)
+        end
+        debugger ""
+
+        class A
+          def debugger
+          end
+        end
+        A.new.debugger
+      )
+      subject.catch(s).valid?.should be_true
+    end
+
+    it "fails if there is a debugger statement" do
+      s = Source.new %(
+        a = 2
+        debugger
+        a = a + 1
+      )
+      subject.catch(s).valid?.should be_false
+    end
+
+    it "reports rule, pos and message" do
+      s = Source.new "debugger"
+      subject.catch(s).valid?.should be_false
+
+      error = s.errors.first
+      error.rule.should_not be_nil
+      error.pos.should eq 1
+      error.message.should eq "Possible forgotten debugger statement detected"
+    end
+  end
+end

src/ameba/rules/debugger_statement.cr

@@ -0,0 +1,20 @@
+module Ameba::Rules
+  # A rule that disallows calls to debugger.
+  #
+  # This is because we don't want debugger breakpoints accidentally being
+  # committed into our codebase.
+  struct DebuggerStatement < Rule
+    def test(source)
+      AST::CallVisitor.new self, source
+    end
+
+    def test(source, node : Crystal::Call)
+      return unless node.name == "debugger" &&
+                    node.args.empty? &&
+                    node.obj.nil?
+
+      source.error self, node.location.try &.line_number,
+        "Possible forgotten debugger statement detected"
+    end
+  end
+end