Disallows while true (#22)

* Disallows `while true`

* Add syntax highlighting in documentation

* Replace `while true` occurrencies

* Add WhileTrue rule to config sample

config/ameba.yml

@@ -88,3 +88,7 @@ UnlessElse:
 VariableNames:
   # Enforces variable names to be in the underscored case.
   Enabled: true
+
+WhileTrue:
+  # Disallows `while` statements with a `true` literal as condition
+  Enabled: true

spec/ameba/rule/while_true_spec.cr

@@ -0,0 +1,42 @@
+require "../../spec_helper"
+
+valid_source = <<-EOF
+a = 1
+loop do
+  a += 1
+  break if a > 5
+end
+EOF
+
+invalid_source = <<-EOF
+a = 1
+while true
+  a += 1
+  break if a > 5
+end
+EOF
+
+module Ameba::Rule
+  subject = WhileTrue.new
+
+  describe WhileTrue do
+    it "passes if there is no `while true`" do
+      source = Source.new valid_source
+      subject.catch(source).should be_valid
+    end
+
+    it "fails if there is `while true`" do
+      source = Source.new invalid_source
+      subject.catch(source).should_not be_valid
+    end
+
+    it "reports rule, pos and message" do
+      source = Source.new invalid_source, "source.cr"
+      subject.catch(source).should_not be_valid
+
+      error = source.errors.first
+      error.location.to_s.should eq "source.cr:2:1"
+      error.message.should eq "While statement using true literal as condition"
+    end
+  end
+end

src/ameba/ast/traverse.cr

@@ -23,6 +23,7 @@ module Ameba::AST
     StringInterpolation,
     Unless,
     Var,
+    While,
   ]
 
   # An AST Visitor used by rules.

src/ameba/rule/redundant_begin.cr

@@ -102,7 +102,7 @@ module Ameba::Rule
     private def def_redundant_begin?(code)
       lexer = Crystal::Lexer.new code
       in_body? = in_argument_list? = false
-      while true
+      loop do
         token = lexer.next_token
 
         case token.type

src/ameba/rule/while_true.cr

@@ -0,0 +1,43 @@
+module Ameba::Rule
+  # A rule that disallows the use of `while true` instead of using the idiomatic `loop`
+  #
+  # For example, this is considered invalid:
+  #
+  # ```
+  # while true
+  #   do_something
+  #   break if some_condition
+  # end
+  # ```
+  #
+  # And should be replaced by the following:
+  #
+  # ```
+  # loop do
+  #   do_something
+  #   break if some_condition
+  # end
+  # ```
+  #
+  # YAML configuration example:
+  #
+  # ```
+  # WhileTrue:
+  #   Enabled: true
+  # ```
+  #
+  struct WhileTrue < Base
+    properties do
+      description = "Disallows while statements with a true literal as condition"
+    end
+
+    def test(source)
+      AST::Visitor.new self, source
+    end
+
+    def test(source, node : Crystal::While)
+      return unless node.cond.true_literal?
+      source.error self, node.location, "While statement using true literal as condition"
+    end
+  end
+end

src/ameba/tokenizer.cr

@@ -45,7 +45,7 @@ module Ameba
 
     private def run_normal_state(lexer, break_on_rcurly = false,
                                  &block : Crystal::Token -> _)
-      while true
+      loop do
         token = @lexer.next_token
         block.call token
 
@@ -63,7 +63,7 @@ module Ameba
     end
 
     private def run_delimiter_state(lexer, token, &block : Crystal::Token -> _)
-      while true
+      loop do
         token = @lexer.next_string_token(token.delimiter_state)
         block.call token
 
@@ -79,7 +79,7 @@ module Ameba
     end
 
     private def run_array_state(lexer, token, &block : Crystal::Token -> _)
-      while true
+      loop do
         lexer.next_string_array_token
         block.call token