Implement a StatsReporter

README.md

@@ -331,6 +331,24 @@ not ok 4 - not-ok2.scss:21:3 SCSSLint::Linter::PrivateNamingConvention
 ok 5 - ok2.scss
 ```
 
+### Stats
+
+Outputs statistics about how many lints of each type were found, and across how many files. This
+reporter can help in cleaning up a large codebase, allowing you to fix and then enable one lint
+type at a time.
+
+```
+15  ColorKeyword                  (across  1 files)
+15  ColorVariable                 (across  1 files)
+11  StringQuotes                  (across 11 files)
+11  EmptyLineBetweenBlocks        (across 11 files)
+ 5  Indentation                   (across  1 files)
+ 5  QualifyingElement             (across  2 files)
+ 4  MergeableSelector             (across  1 files)
+--  ----------------------        -----------------
+66  total                         (across 12 files)
+```
+
 ### Plugins
 
 There are also formatters that integrate with third-party tools which are available as plugins.

lib/scss_lint/reporter/stats_reporter.rb

@@ -0,0 +1,39 @@
+module SCSSLint
+  # Reports a single line per lint.
+  class Reporter::StatsReporter < Reporter
+    def report_lints # rubocop:disable Metrics/AbcSize
+      return unless lints.any?
+
+      stats = organize_stats
+      total_lints = lints.length
+      linter_name_length =
+        stats.inject('') { |memo, stat| memo.length > stat[0].length ? memo : stat[0] }.length
+      total_files = lints.group_by(&:filename).size
+
+      # Math.log10(1) is 0; avoid this by using at least 1.
+      lint_count_length = [1, Math.log10(total_lints).ceil].max
+      file_count_length = [1, Math.log10(total_files).ceil].max
+
+      str = ''
+      stats.each do |linter_name, lint_count, file_count|
+        str << "%#{lint_count_length}d  %-#{linter_name_length}s" % [lint_count, linter_name]
+        str << "        (across %#{file_count_length}d files)\n" % [file_count]
+      end
+      str << "#{'-' * lint_count_length}  #{'-' * linter_name_length}"
+      str << "        #{'-' * (file_count_length + 15)}\n"
+      str << "%#{lint_count_length}d  #{'total'.ljust(linter_name_length)}" % total_lints
+      str << "        (across %#{file_count_length}d files)\n" % total_files
+      str
+    end
+
+    def organize_stats
+      lints
+        .group_by(&:linter)
+        .sort_by { |_, lints_by_linter| -lints_by_linter.size }
+        .inject([]) do |ary, (linter, lints_by_linter)|
+          file_count = lints_by_linter.group_by(&:filename).size
+          ary << [linter.name, lints_by_linter.size, file_count]
+        end
+    end
+  end
+end

spec/scss_lint/reporter/stats_reporter_spec.rb

@@ -0,0 +1,115 @@
+require 'spec_helper'
+
+describe SCSSLint::Reporter::StatsReporter do
+  class SCSSLint::Linter::FakeLinter1 < SCSSLint::Linter; end
+  class SCSSLint::Linter::FakeLinter2 < SCSSLint::Linter; end
+
+  let(:logger) { SCSSLint::Logger.new($stdout) }
+  let(:linter_1) { SCSSLint::Linter::FakeLinter1.new }
+  let(:linter_2) { SCSSLint::Linter::FakeLinter2.new }
+  subject { SCSSLint::Reporter::StatsReporter.new(lints, [], logger) }
+
+  def new_lint(linter, filename, line)
+    SCSSLint::Lint.new(linter, filename, SCSSLint::Location.new(line), 'Description', :warning)
+  end
+
+  describe '#report_lints' do
+    context 'when there are no lints' do
+      let(:lints) { [] }
+
+      it 'returns nil' do
+        subject.report_lints.should be_nil
+      end
+    end
+
+    context 'when there are lints from one linter in one file' do
+      let(:lints) do
+        [new_lint(linter_1, 'a.scss', 10), new_lint(linter_1, 'a.scss', 20)]
+      end
+
+      it 'prints one line per linter with lints, plus 2 summary lines' do
+        subject.report_lints.count("\n").should eq 3
+      end
+
+      it 'prints the name of each linter with lints' do
+        subject.report_lints.scan(linter_1.name).count.should eq 1
+      end
+
+      it 'prints the number of lints per linter' do
+        subject.report_lints.should include '2  FakeLinter1'
+      end
+
+      it 'prints the number of files where each linter found lints' do
+        subject.report_lints.should include '1 files'
+      end
+
+      it 'prints the total lints and total lines' do
+        subject.report_lints.should match /2  total +\(across 1/
+      end
+    end
+
+    context 'when there are lints from multiple linters in one file' do
+      let(:lints) do
+        [new_lint(linter_1, 'a.scss', 10),
+         new_lint(linter_1, 'a.scss', 20),
+         new_lint(linter_2, 'a.scss', 30)]
+      end
+
+      it 'prints one line per linter with lints, plus 2 summary lines' do
+        subject.report_lints.count("\n").should eq 4
+      end
+
+      it 'prints the name of each linter with lints' do
+        subject.report_lints.scan(linter_1.name).count.should eq 1
+        subject.report_lints.scan(linter_2.name).count.should eq 1
+      end
+
+      it 'prints the number of lints per linter' do
+        subject.report_lints.should include '2  FakeLinter1'
+        subject.report_lints.should include '1  FakeLinter2'
+      end
+
+      it 'prints the number of files where each linter found lints' do
+        subject.report_lints.scan(/FakeLinter\d +\(across 1 files/).count.should eq 2
+      end
+
+      it 'prints the total lints and total lines' do
+        subject.report_lints.should match /3  total +\(across 1/
+      end
+    end
+
+    context 'when there are lints from multiple linters in multiple files' do
+      let(:lints) do
+        [new_lint(linter_1, 'a.scss', 10),
+         new_lint(linter_1, 'a.scss', 20),
+         new_lint(linter_2, 'a.scss', 30),
+         new_lint(linter_1, 'b.scss', 15),
+         new_lint(linter_2, 'b.scss', 25),
+         new_lint(linter_1, 'c.scss', 100)]
+      end
+
+      it 'prints one line per linter with lints, plus 2 summary lines' do
+        subject.report_lints.count("\n").should eq 4
+      end
+
+      it 'prints the name of each linter with lints' do
+        subject.report_lints.scan(linter_1.name).count.should eq 1
+        subject.report_lints.scan(linter_2.name).count.should eq 1
+      end
+
+      it 'prints the number of lints per linter' do
+        subject.report_lints.should include '4  FakeLinter1'
+        subject.report_lints.should include '2  FakeLinter2'
+      end
+
+      it 'prints the number of files where each linter found lints' do
+        subject.report_lints.scan(/FakeLinter2 +\(across 2 files/).count.should eq 1
+        subject.report_lints.scan(/FakeLinter1 +\(across 3 files/).count.should eq 1
+      end
+
+      it 'prints the total lints and total lines' do
+        subject.report_lints.should match /6  total +\(across 3/
+      end
+    end
+  end
+end