Add Trailing Empty Lines linter

HAML documents should not contain empty lines at the end of the file.

Inspired by Slim lint's `TrailingBlankLines`


Close sds#422

CHANGELOG.md

@@ -1,5 +1,9 @@
 # HAML-Lint Changelog
 
+# unreleased
+
+* Add `TrailingEmptyLines` linter
+
 # 0.48.0
 
 * Fix `Marshal.dump` error when using `--parallel` option and `RepeatedId` Linter

config/default.yml

@@ -105,6 +105,9 @@ linters:
   TagName:
     enabled: true
 
+  TrailingEmptyLines:
+    enabled: true
+
   TrailingWhitespace:
     enabled: true
 

lib/haml_lint/linter/README.md

@@ -29,6 +29,7 @@ Below is a list of linters supported by `haml-lint`, ordered alphabetically.
 * [SpaceBeforeScript](#spacebeforescript)
 * [SpaceInsideHashAttributes](#spaceinsidehashattributes)
 * [TagName](#tagname)
+* [TrailingEmptyLines](#trailingemptylines)
 * [TrailingWhitespace](#trailingwhitespace)
 * [UnnecessaryInterpolation](#unnecessaryinterpolation)
 * [UnnecessaryStringOutput](#unnecessarystringoutput)
@@ -711,6 +712,10 @@ general, as it is easier to type and matches the convention of many developer
 tools. If you are writing HAML to output XML documents, however, it is a strict
 requirement.
 
+## TrailingEmptyLines
+
+HAML documents should not contain empty lines at the end of the file.
+
 ## TrailingWhitespace
 
 HAML documents should not contain trailing whitespace (spaces or tabs) on any

lib/haml_lint/linter/trailing_empty_lines.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module HamlLint
+  # Checks for trailing empty lines.
+  class Linter::TrailingEmptyLines < Linter
+    include LinterRegistry
+
+    DummyNode = Struct.new(:line)
+
+    def visit_root(root)
+      return if document.source.empty?
+      line_number = document.last_non_empty_line
+
+      node = root.node_for_line(line_number)
+      return if node.disabled?(self)
+
+      return unless document.source.end_with?("\n\n")
+
+      record_lint(line_number, 'Files should not end with trailing empty lines')
+    end
+  end
+end

spec/haml_lint/linter/trailing_empty_lines_spec.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+describe HamlLint::Linter::TrailingEmptyLines do
+  include_context 'linter'
+
+  context 'when the file is empty' do
+    let(:haml) { '' }
+
+    it { should_not report_lint }
+  end
+
+  context 'when file ends with a single newline' do
+    let(:haml) { "%h1 Hello\n" }
+
+    it { should_not report_lint }
+  end
+
+  context 'when file contains multiple newlines' do
+    let(:haml) { "%h1 Hello\n\n" }
+
+    it { should report_lint line: 1 }
+
+    context 'but the linter is disabled in the file' do
+      let(:haml) { "-# haml-lint:disable TrailingEmptyLines\n" + super() }
+
+      it { should_not report_lint }
+    end
+  end
+end

test.haml

@@ -0,0 +1 @@
+%h1 Hello