Add FinalNewline linter

Enforces the presence of a final trailing newline in files.

CHANGELOG.md

@@ -5,6 +5,8 @@
 * Improve bug reporting instructions in error message
 * Add `Indentation` linter to enforce that spaces or tabs are used for
   indentation (enabled by default and defaults to spaces)
+* Add `FinalNewline` linter to enforce the presence of a final newline
+  in files
 
 ## 0.14.1
 

config/default.yml

@@ -27,6 +27,10 @@ linters:
   EmptyScript:
     enabled: true
 
+  FinalNewline:
+    enabled: true
+    present: true
+
   HtmlAttributes:
     enabled: true
 

lib/haml_lint/linter/README.md

@@ -8,6 +8,7 @@ Below is a list of linters supported by `haml-lint`, ordered alphabetically.
 * [ConsecutiveComments](#consecutivecomments)
 * [ConsecutiveSilentScripts](#consecutivesilentscripts)
 * [EmptyScript](#emptyscript)
+* [FinalNewline](#finalnewline)
 * [HtmlAttributes](#htmlattributes)
 * [ImplicitDiv](#implicitdiv)
 * [Indentation](#indentation)
@@ -144,6 +145,19 @@ Don't write empty scripts.
 
 These serve no purpose and are usually left behind by mistake.
 
+## FinalNewline
+
+Files should always have a final newline. This results in better diffs when
+adding lines to the file, since SCM systems such as `git` won't think that you
+touched the last line if you append to the end of a file.
+
+You can customize whether or not a final newline exists with the `present`
+option.
+
+Configuration Option | Description
+---------------------|---------------------------------------------------------
+`present`            | Whether a final newline should be present (default `true`)
+
 ## HtmlAttributes
 
 Don't use the

lib/haml_lint/linter/final_newline.rb

@@ -0,0 +1,21 @@
+module HamlLint
+  # Checks for final newlines at the end of a file.
+  class Linter::FinalNewline < Linter
+    include LinterRegistry
+
+    def visit_root(_node)
+      return if document.source.empty?
+
+      dummy_node = Struct.new(:line).new(document.source_lines.count)
+      ends_with_newline = document.source.end_with?("\n")
+
+      if config['present']
+        record_lint(dummy_node,
+                    'Files should end with a trailing newline') unless ends_with_newline
+      else
+        record_lint(dummy_node,
+                    'Files should not end with a trailing newline') if ends_with_newline
+      end
+    end
+  end
+end

spec/haml_lint/linter/final_newline_spec.rb

@@ -0,0 +1,49 @@
+require 'spec_helper'
+
+describe HamlLint::Linter::FinalNewline do
+  include_context 'linter'
+
+  context 'when trailing newline is preferred' do
+    let(:config) { super().merge('present' => true) }
+
+    context 'when the file is empty' do
+      let(:haml) { '' }
+
+      it { should_not report_lint }
+    end
+
+    context 'when the file ends with a newline' do
+      let(:haml) { "%span\n" }
+
+      it { should_not report_lint }
+    end
+
+    context 'when the file does not end with a newline' do
+      let(:haml) { '%span' }
+
+      it { should report_lint line: 1 }
+    end
+  end
+
+  context 'when no trailing newline is preferred' do
+    let(:config) { super().merge('present' => false) }
+
+    context 'when the file is empty' do
+      let(:haml) { '' }
+
+      it { should_not report_lint }
+    end
+
+    context 'when the file ends with a newline' do
+      let(:haml) { "%span\n" }
+
+      it { should report_lint line: 1 }
+    end
+
+    context 'when the file does not end with a newline' do
+      let(:haml) { '%span' }
+
+      it { should_not report_lint }
+    end
+  end
+end

spec/haml_lint/rake_task_spec.rb

@@ -24,7 +24,7 @@ def run_task
   end
 
   context 'when Haml document is valid' do
-    let(:haml) { '%p Hello world' }
+    let(:haml) { "%p Hello world\n" }
 
     it 'executes without error' do
       expect { run_task }.not_to raise_error