Add Lint/Formatting rule

spec/ameba/rule/lint/formatting_spec.cr

@@ -0,0 +1,48 @@
+require "../../../spec_helper"
+
+module Ameba::Rule::Lint
+  describe Formatting do
+    subject = Formatting.new
+
+    it "passes if source is formatted" do
+      expect_no_issues subject, <<-CRYSTAL
+        def method(a, b)
+          a + b
+        end
+
+        CRYSTAL
+    end
+
+    it "reports if source is not formatted" do
+      expect_issue subject, <<-CRYSTAL
+        def method(a,b)
+        # ^{} error: Use built-in formatter to format this source
+        end
+        CRYSTAL
+    end
+
+    context "properties" do
+      context "#fail_on_error" do
+        it "passes on formatter errors by default" do
+          rule = Formatting.new
+
+          expect_no_issues rule, <<-CRYSTAL
+            def method(a, b)
+              a + b
+            CRYSTAL
+        end
+
+        it "reports on formatter errors when enabled" do
+          rule = Formatting.new
+          rule.fail_on_error = true
+
+          expect_issue rule, <<-CRYSTAL
+            def method(a, b)
+              a + b
+                 # ^ error: Error while formatting: expecting identifier 'end', not 'EOF'
+            CRYSTAL
+        end
+      end
+    end
+  end
+end

spec/ameba/runner_spec.cr

@@ -175,10 +175,11 @@ module Ameba
 
       it "depends on the level of severity" do
         rules = Rule.rules.map &.new.as(Rule::Base)
-        s = Source.new %q(WrongConstant = 5)
-        Runner.new(rules, [s], formatter, Severity::Error).run.success?.should be_true
-        Runner.new(rules, [s], formatter, Severity::Warning).run.success?.should be_true
-        Runner.new(rules, [s], formatter, Severity::Convention).run.success?.should be_false
+        source = Source.new "WrongConstant = 5\n"
+
+        Runner.new(rules, [source], formatter, :error).run.success?.should be_true
+        Runner.new(rules, [source], formatter, :warning).run.success?.should be_true
+        Runner.new(rules, [source], formatter, :convention).run.success?.should be_false
       end
 
       it "returns false if issue is disabled" do

src/ameba/rule/lint/formatting.cr

@@ -0,0 +1,65 @@
+require "compiler/crystal/formatter"
+
+module Ameba::Rule::Lint
+  # A rule that verifies syntax formatting according to the
+  # Crystal's built-in formatter.
+  #
+  # For example, this syntax is invalid:
+  #
+  #     def foo(a,b,c=0)
+  #       #foobar
+  #       a+b+c
+  #     end
+  #
+  # And should be properly written:
+  #
+  #     def foo(a, b, c = 0)
+  #       # foobar
+  #       a + b + c
+  #     end
+  #
+  # YAML configuration example:
+  #
+  # ```
+  # Lint/Formatting:
+  #   Enabled: true
+  #   FailOnError: false
+  # ```
+  class Formatting < Base
+    properties do
+      description "Reports not formatted sources"
+      fail_on_error false
+    end
+
+    MSG       = "Use built-in formatter to format this source"
+    MSG_ERROR = "Error while formatting: %s"
+
+    private LOCATION = {1, 1}
+
+    def test(source)
+      source_code = source.code
+      result = Crystal.format(source_code, source.path)
+      return if result == source_code
+
+      source_lines = source_code.lines
+      return if source_lines.empty?
+
+      end_location = {
+        source_lines.size,
+        source_lines.last.size + 1,
+      }
+
+      issue_for LOCATION, MSG do |corrector|
+        corrector.replace(LOCATION, end_location, result)
+      end
+    rescue ex : Crystal::SyntaxException
+      if fail_on_error?
+        issue_for({ex.line_number, ex.column_number}, MSG_ERROR % ex.message)
+      end
+    rescue ex
+      if fail_on_error?
+        issue_for(LOCATION, MSG_ERROR % ex.message)
+      end
+    end
+  end
+end