Add solargraph pre-commit hook for typechecking (#871)

[Solargraph](https://github.com/castwide/solargraph) supports
typechecking Ruby files based on YARD tags - combined with overcommit,
it can be used in an incremental way on large untyped codebases.

Author: apiology

config/default.yml

@@ -799,6 +799,20 @@ PreCommit:
     install_command: 'gem install slim_lint'
     include: '**/*.slim'
 
+  Solargraph:
+    enabled: false
+    description: 'Typecheck with Solargraph'
+    requires_files: true
+    required_executable: 'solargraph'
+    install_command: 'gem install solargraph'
+    flags: ['typecheck', '--level', 'strong']
+    include: '**/*.rb'
+    exclude:
+      - 'spec/**/*.rb'
+      - 'test/**/*.rb'
+      - 'vendor/**/*.rb'
+      - '.bundle/**/*.rb'
+
   Sorbet:
     enabled: false
     description: 'Analyze with Sorbet'

lib/overcommit/hook/pre_commit/solargraph.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require 'overcommit'
+require 'overcommit/hook/pre_commit/base'
+
+module Overcommit
+  module Hook
+    module PreCommit
+      # Runs `solargraph typecheck` against any modified Ruby files.
+      #
+      # @see https://github.com/castwide/solargraph
+      class Solargraph < Base
+        MESSAGE_REGEX = /^\s*(?<file>(?:\w:)?[^:]+):(?<line>\d+) - /.freeze
+
+        def run
+          result = execute(command, args: applicable_files)
+          return :pass if result.success?
+
+          stderr_lines = remove_harmless_glitches(result.stderr)
+          violation_lines = result.stdout.split("\n").grep(MESSAGE_REGEX)
+          if violation_lines.empty?
+            if stderr_lines.empty?
+              [:fail, 'Solargraph failed to run']
+            else
+              # let's feed it stderr so users see the errors
+              extract_messages(stderr_lines, MESSAGE_REGEX)
+            end
+          else
+            extract_messages(violation_lines, MESSAGE_REGEX)
+          end
+        end
+
+        private
+
+        # @param stderr [String]
+        #
+        # @return [Array<String>]
+        def remove_harmless_glitches(stderr)
+          stderr.split("\n").reject do |line|
+            line.include?('[WARN]') ||
+              line.include?('warning: parser/current is loading') ||
+              line.include?('Please see https://github.com/whitequark')
+          end
+        end
+      end
+    end
+  end
+end

spec/overcommit/hook/pre_commit/solargraph_spec.rb

@@ -0,0 +1,110 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Overcommit::Hook::PreCommit::Solargraph do
+  let(:config) do
+    Overcommit::ConfigurationLoader.default_configuration.merge(
+      Overcommit::Configuration.new(
+        'PreCommit' => {
+          'Solargraph' => {
+            'problem_on_unmodified_line' => problem_on_unmodified_line
+          }
+        }
+      )
+    )
+  end
+  let(:problem_on_unmodified_line) { 'ignore' }
+  let(:context) { double('context') }
+  let(:messages) { subject.run }
+  let(:result) { double('result') }
+  subject { described_class.new(config, context) }
+
+  before do
+    subject.stub(:applicable_files).and_return(%w[file1.rb file2.rb])
+    result.stub(:stderr).and_return(stderr)
+    result.stub(:stdout).and_return(stdout)
+  end
+
+  context 'when Solargraph exits successfully' do
+    before do
+      result.stub(:success?).and_return(true)
+      subject.stub(:execute).and_return(result)
+    end
+
+    context 'and it printed a message to stderr' do
+      let(:stderr) { 'stderr unexpected message that must be fine since command successful' }
+      let(:stdout) { '' }
+      it { should pass }
+    end
+
+    context 'and it printed a message to stdout' do
+      let(:stderr) { '' }
+      let(:stdout) { 'stdout message that must be fine since command successful' }
+      it { should pass }
+    end
+  end
+
+  context 'when Solargraph exits unsucessfully' do
+    before do
+      result.stub(:success?).and_return(false)
+      subject.stub(:execute).and_return(result)
+    end
+
+    context 'and it reports typechecking issues' do
+      let(:stdout) do
+        normalize_indent(<<-MSG)
+          /home/username/src/solargraph-rails/file1.rb:36 - Unresolved constant Solargraph::Parser::Legacy::NodeChainer
+          /home/username/src/solargraph-rails/file2.rb:44 - Unresolved call to []
+          /home/username/src/solargraph-rails/file2.rb:99 - Unresolved call to []
+          Typecheck finished in 8.921023999806494 seconds.
+          189 problems found in 14 of 16 files.
+        MSG
+      end
+
+      ['', 'unexpected output'].each do |stderr_string|
+        context "with stderr output of #{stderr_string.inspect}" do
+          let(:stderr) { stderr_string }
+
+          it { should fail_hook }
+          it 'reports only three errors and assumes stderr is harmless' do
+            expect(messages.size).to eq 3
+          end
+          it 'parses filename' do
+            expect(messages.first.file).to eq '/home/username/src/solargraph-rails/file1.rb'
+          end
+          it 'parses line number of messages' do
+            expect(messages.first.line).to eq 36
+          end
+          it 'parses and returns error message content' do
+            msg = '/home/username/src/solargraph-rails/file1.rb:36 - Unresolved constant Solargraph::Parser::Legacy::NodeChainer'
+            expect(messages.first.content).to eq msg
+          end
+        end
+      end
+    end
+
+    context 'but it reports no typechecking issues' do
+      let(:stdout) do
+        normalize_indent(<<-MSG)
+           Typecheck finished in 8.095239999704063 seconds.
+           0 problems found in 0 of 16 files.
+        MSG
+      end
+
+      context 'with no stderr output' do
+        let(:stderr) { '' }
+        it 'should return no messages' do
+          expect(messages).to eq([:fail, 'Solargraph failed to run'])
+        end
+      end
+
+      context 'with stderr output' do
+        let(:stderr) { 'something' }
+        it 'should raise' do
+          expect { messages }.to raise_error(Overcommit::Exceptions::MessageProcessingError)
+        end
+      end
+    end
+  end
+end