New rule: trailing blank lines

spec/ameba/rules/trailing_blank_lines_spec.cr

@@ -0,0 +1,37 @@
+require "../../spec_helper"
+
+module Ameba::Rules
+  subject = TrailingBlankLines.new
+
+  describe TrailingBlankLines do
+    it "passes if there is no blank lines at the end" do
+      source = Source.new "", "no-blankline"
+      subject.catch(source).valid?.should be_true
+    end
+
+    it "fails if there is a blank line at the end of a source" do
+      source = Source.new "", "a = 1\n \n "
+      subject.catch(source).valid?.should be_false
+    end
+
+    it "passes if source is empty" do
+      source = Source.new "", ""
+      subject.catch(source).valid?.should be_true
+    end
+
+    it "passes if last line is not blank" do
+      source = Source.new "", "\n\n\n puts 22"
+      subject.catch(source).valid?.should be_true
+    end
+
+    it "reports rule, pos and message" do
+      source = Source.new "", "a = 1\n\n "
+      subject.catch(source)
+
+      error = source.errors.first
+      error.rule.should_not be_nil
+      error.pos.should eq 3
+      error.message.should eq "Blank lines detected at the end of the file"
+    end
+  end
+end

src/ameba/rule.cr

@@ -1,6 +1,7 @@
 module Ameba
   RULES = [
     Rules::LineLength,
+    Rules::TrailingBlankLines,
     Rules::TrailingWhitespace,
   ]
 

src/ameba/rules/trailing_blank_lines.cr

@@ -0,0 +1,8 @@
+# A rule that disallows trailing blank lines at the end of the source file.
+
+Ameba.rule TrailingBlankLines do |source|
+  if source.lines.size > 1 && source.lines[-2, 2].join.strip == ""
+    source.error self, source.lines.size,
+      "Blank lines detected at the end of the file"
+  end
+end