Move to HookContexts

Change-Id: Ib9082dd93b5019c79e4117ec60f9fd11cd905786
Reviewed-on: http://gerrit.causes.com/35561
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>

Author: sds

config/default.yml

@@ -8,6 +8,11 @@
 # to the root of the repository.
 plugin_directory: '.githooks'
 
+# Hooks that run after HEAD changes or a file is explicitly checked out. Useful
+# for updating source tags (e.g. via ctags) or warning about new migrations,
+# etc.
+post_checkout:
+
 # Hooks that are run after `git commit` is executed, before the commit message
 # editor is displayed. These hooks are ideal for syntax checkers, linters, and
 # other checks that you want to run before you allow a commit object to be

lib/overcommit.rb

@@ -3,8 +3,9 @@
 require 'overcommit/configuration'
 require 'overcommit/configuration_loader'
 require 'overcommit/hook/base'
+require 'overcommit/hook_context/base'
+require 'overcommit/hook_context'
 require 'overcommit/hook_runner'
-require 'overcommit/hook_runner/base'
 require 'overcommit/installer'
 require 'overcommit/logger'
 require 'overcommit/reporter'

lib/overcommit/configuration.rb

@@ -49,7 +49,8 @@ def apply_environment!(hook_type, env)
       if skipped_hooks.include?('all') || skipped_hooks.include?('ALL')
         @hash[hook_type]['ALL']['skip'] = true
       else
-        skipped_hooks.each do |hook_name|
+        skipped_hooks.select { |hook_name| hook_exists?(hook_type, hook_name) }.
+                      each do |hook_name|
           @hash[hook_type][hook_name] ||= {}
           @hash[hook_type][hook_name]['skip'] = true
         end
@@ -62,6 +63,11 @@ def apply_environment!(hook_type, env)
 
   private
 
+    def hook_exists?(hook_type, hook_name)
+      File.exist?(File.join(OVERCOMMIT_HOME, 'lib', 'overcommit', 'hook',
+                            hook_type, "#{hook_name}.rb"))
+    end
+
     # Validates the configuration for any invalid options, normalizing it where
     # possible.
     def validate

lib/overcommit/exceptions.rb

@@ -6,7 +6,7 @@ class ConfigurationError < StandardError; end
   class HookLoadError < StandardError; end
 
   # Raised when a {HookRunner} could not be loaded.
-  class HookRunnerLoadError < StandardError; end
+  class HookContextLoadError < StandardError; end
 
   # Raised when a installation target is not a valid git repository.
   class InvalidGitRepo < StandardError; end

lib/overcommit/hook/base.rb

@@ -1,11 +1,15 @@
-require 'wopen3'
+require 'forwardable'
 
 module Overcommit::Hook
   # Functionality common to all hooks.
   class Base
-    def initialize(config, hook_runner)
+    extend Forwardable
+
+    def_delegators :@context, :staged_files
+
+    def initialize(config, context)
       @config = config.hook_config(self)
-      @hook_runner = hook_runner
+      @context = context
     end
 
     # Runs the hook.
@@ -47,6 +51,14 @@ def run?
         !(requires_modified_files? && applicable_files.empty?)
     end
 
+    def in_path?(cmd)
+      Overcommit::Utils.in_path?(cmd)
+    end
+
+    def command(cmd)
+      Overcommit::Utils.command(cmd)
+    end
+
     # Gets a list of staged files that apply to this hook based on its
     # configured `include` and `exclude` lists.
     def applicable_files
@@ -55,12 +67,6 @@ def applicable_files
 
   private
 
-    def staged_files
-      @hook_runner.staged_files
-    end
-
-    # Returns whether the specified file is applicable to this hook based on the
-    # hook's `include` and `exclude` file glob patterns.
     def applicable_file?(file)
       includes = Array(@config['include']).map { |glob| convert_glob_to_absolute(glob) }
       included = includes.empty? ||
@@ -81,73 +87,5 @@ def convert_glob_to_absolute(glob)
         File.join(repo_root, glob)
       end
     end
-
-    # Returns the set of line numbers corresponding to the lines that were
-    # changed in a specified file.
-    def modified_lines(staged_file)
-      @modified_lines ||= {}
-      @modified_lines[staged_file] ||= extract_modified_lines(staged_file)
-    end
-
-    DIFF_HUNK_REGEX = /
-      ^@@\s
-      [^\s]+\s           # Ignore old file range
-      \+(\d+)(?:,(\d+))? # Extract range of hunk containing start line and number of lines
-      \s@@.*$
-    /x
-
-    def extract_modified_lines(staged_file)
-      lines = Set.new
-
-      `git diff --no-ext-diff --cached -U0 -- #{staged_file}`.
-        scan(DIFF_HUNK_REGEX) do |start_line, lines_added|
-
-        lines_added = (lines_added || 1).to_i # When blank, one line was added
-        cur_line    = start_line.to_i
-
-        lines_added.times do
-          lines.add cur_line
-          cur_line += 1
-        end
-      end
-
-      lines
-    end
-
-    # Returns whether a command can be found given the current environment path.
-    def in_path?(cmd)
-      exts = ENV['PATHEXT'] ? ENV['PATHEXT'].split(';') : ['']
-      ENV['PATH'].split(File::PATH_SEPARATOR).each do |path|
-        exts.each do |ext|
-          exe = File.join(path, "#{cmd}#{ext}")
-          return true if File.executable? exe
-        end
-      end
-      false
-    end
-
-    # Wrap external subshell calls. This is necessary in order to allow
-    # Overcommit to call other Ruby executables without requiring that they be
-    # specified in Overcommit's Gemfile--a nasty consequence of using
-    # `bundle exec overcommit` while developing locally.
-    def command(command)
-      with_environment 'RUBYOPT' => nil do
-        Wopen3.system(command)
-      end
-    end
-
-    # Calls a block of code with a modified set of environment variables,
-    # restoring them once the code has executed.
-    def with_environment(env, &block)
-      old_env = {}
-      env.each do |var, value|
-        old_env[var] = ENV[var.to_s]
-        ENV[var.to_s] = value
-      end
-
-      yield
-    ensure
-      old_env.each { |var, value| ENV[var.to_s] = value }
-    end
   end
 end

lib/overcommit/hook/commit_msg/base.rb

@@ -1,8 +1,10 @@
+require 'forwardable'
+
 module Overcommit::Hook::CommitMsg
   # Functionality common to all commit-msg hooks.
   class Base < Overcommit::Hook::Base
-    def commit_message
-      @hook_runner.commit_message
-    end
+    extend Forwardable
+
+    def_delegators :@context, :commit_message
   end
 end

lib/overcommit/hook/post_checkout/base.rb

@@ -0,0 +1,11 @@
+require 'forwardable'
+
+module Overcommit::Hook::PostCheckout
+  # Functionality common to all post-checkout hooks.
+  class Base < Overcommit::Hook::Base
+    extend Forwardable
+
+    def_delegator :@context,
+                  *%i[previous_head new_head branch_checkout? file_checkout?]
+  end
+end

lib/overcommit/hook/pre_commit/base.rb

@@ -1,5 +1,10 @@
+require 'forwardable'
+
 module Overcommit::Hook::PreCommit
   # Functionality common to all pre-commit hooks.
   class Base < Overcommit::Hook::Base
+    extend Forwardable
+
+    def_delegators :@context, :modified_lines
   end
 end

lib/overcommit/hook_context.rb

@@ -0,0 +1,21 @@
+# Utility module which manages the creation of {HookContext}s.
+module Overcommit::HookContext
+  def self.create(hook_type, config, args, input)
+    require "overcommit/hook_context/#{hook_type.gsub('-', '_')}"
+
+    Overcommit::HookContext.const_get(hook_type_to_class_name(hook_type))
+                           .new(config, args, input)
+  rescue LoadError, NameError => error
+    # Could happen when a symlink was created for a hook type Overcommit does
+    # not yet support.
+    raise Overcommit::Exceptions::HookContextLoadError,
+          "Unable to load '#{hook_type}' hook context: '#{error}'",
+          error.backtrace
+  end
+
+private
+
+  def self.hook_type_to_class_name(hook_type)
+    hook_type.split('-').map { |s| s.capitalize }.join
+  end
+end

lib/overcommit/hook_context/base.rb

@@ -0,0 +1,27 @@
+module Overcommit::HookContext
+  # Contains helpers related to the context with which a hook is being run.
+  #
+  # It acts as an adapter to the arguments passed to the hook, as well as
+  # context-specific information such as staged files, providing a single source
+  # of truth for this context.
+  #
+  # This is also important to house in a separate object so that any
+  # calculations can be memoized across all hooks in a single object, which
+  # helps with performance.
+  class Base
+    def initialize(config, args, input)
+      @config = config
+      @args = args
+      @input = input
+    end
+
+    # Get a list of added, copied, or modified files that have been staged.
+    # Renames and deletions are ignored, since there should be nothing to check.
+    def staged_files
+      @staged_files ||=
+        `git diff --cached --name-only --diff-filter=ACM --ignore-submodules=all`.
+          split("\n").
+          map { |relative_file| File.expand_path(relative_file) }
+    end
+  end
+end

lib/overcommit/hook_runner/commit_msg.rb lib/overcommit/hook_context/commit_msg.rb

@@ -1,5 +1,4 @@
-module Overcommit::HookRunner
-  # Manages loading and running commit-msg hooks.
+module Overcommit::HookContext
   class CommitMsg < Base
     # User commit message stripped of comments and diff (from verbose output)
     def commit_message
@@ -8,12 +7,12 @@ def commit_message
         take_while { |line| !line.start_with?('diff --git') }
     end
 
+  private
+
     def raw_commit_message
       @raw_commit_message ||= ::IO.readlines(commit_message_file)
     end
 
-  private
-
     def commit_message_file
       unless @args[0] && ::File.exist?(@args[0])
         fail 'Not running in the context of a commit message'

lib/overcommit/hook_context/post_checkout.rb

@@ -0,0 +1,24 @@
+module Overcommit::HookContext
+  class PostCheckout < Base
+    # Returns the ref of the HEAD that we transitioned from.
+    def previous_head
+      @args[0]
+    end
+
+    # Returns the ref of the new current HEAD.
+    def new_head
+      @args[1]
+    end
+
+    # Returns whether this checkout was the result of changing/updating a
+    # branch.
+    def branch_checkout?
+      @args[2].to_i == 1
+    end
+
+    # Returns whether this checkout was for a single file.
+    def file_checkout?
+      !branch_checkout?
+    end
+  end
+end

lib/overcommit/hook_context/pre_commit.rb

@@ -0,0 +1,41 @@
+module Overcommit::HookContext
+  # Contains helpers related to contextual information used by pre-commit hooks.
+  #
+  # This includes staged files, which lines of those files have been modified,
+  # etc.
+  class PreCommit < Base
+    # Returns the set of line numbers corresponding to the lines that were
+    # changed in a specified file.
+    def modified_lines(staged_file)
+      @modified_lines ||= {}
+      @modified_lines[staged_file] ||= extract_modified_lines(staged_file)
+    end
+
+  private
+
+    DIFF_HUNK_REGEX = /
+      ^@@\s
+      [^\s]+\s           # Ignore old file range
+      \+(\d+)(?:,(\d+))? # Extract range of hunk containing start line and number of lines
+      \s@@.*$
+    /x
+
+    def extract_modified_lines(staged_file)
+      lines = Set.new
+
+      `git diff --no-ext-diff --cached -U0 -- #{staged_file}`.
+        scan(DIFF_HUNK_REGEX) do |start_line, lines_added|
+
+        lines_added = (lines_added || 1).to_i # When blank, one line was added
+        cur_line    = start_line.to_i
+
+        lines_added.times do
+          lines.add cur_line
+          cur_line += 1
+        end
+      end
+
+      lines
+    end
+  end
+end