Gracefully handle pre-commit git stash failures

When attempting to `git stash` in the `setup_environment` method of the
`PreCommit` hook context, it was possible for the underlying execution
of `git stash` to fail.

Handle this case by actually inspecting the status code of `git stash`
before continuing the hook run.

Change-Id: I05bcf22af55753bdda2e56f360bae78de4415910
Reviewed-on: http://gerrit.causes.com/40969
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: sds

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 * Fix bug where incorrect "hook run interrupted" message displayed when
   hook run failed
+* Gracefully handle `git stash` failures in pre-commit hook runs
 
 ## 0.14.1
 

lib/overcommit/exceptions.rb

@@ -5,6 +5,9 @@ class ConfigurationError < StandardError; end
   # Raised when trying to read/write to/from the local repo git config fails.
   class GitConfigError < StandardError; end
 
+  # Raised when a {HookContext} is unable to setup the environment before a run.
+  class HookSetupFailed < StandardError; end
+
   # Raised when a hook run was cancelled by the user.
   class HookCancelled < StandardError; end
 

lib/overcommit/hook_context/pre_commit.rb

@@ -16,10 +16,22 @@ def setup_environment
       Overcommit::GitRepo.store_cherry_pick_state
 
       if !initial_commit? && any_changes?
+        @stash_attempted = true
+
+        result = Overcommit::Utils.execute(
+          %w[git stash save --keep-index --quiet] +
+          ["Overcommit: Stash of repo state before hook run at #{Time.now}"]
+        )
+
+        unless result.success?
+          # Failure to stash in this case is likely due to a configuration
+          # issue (e.g. author/email not set or GPG signing key incorrect)
+          raise Overcommit::Exceptions::HookSetupFailed,
+                "Unable to setup environment for #{hook_script_name} hook run:" \
+                "\n#{result.stderr}"
+        end
+
         @changes_stashed = true
-        `git stash save --keep-index --quiet #{<<-MSG}`
-          "Overcommit: Stash of repo state before hook run at #{Time.now}"
-        MSG
       end
 
       # While running the hooks make it appear as if nothing changed
@@ -29,7 +41,7 @@ def setup_environment
     # Restore unstaged changes and reset file modification times so it appears
     # as if nothing ever changed.
     def cleanup_environment
-      unless initial_commit?
+      unless initial_commit? || (@stash_attempted && !@changes_stashed)
         `git reset --hard &> /dev/null` # Ensure working tree is clean before popping stash
       end
 

template-dir/hooks/overcommit-hook

@@ -78,6 +78,9 @@ rescue Overcommit::Exceptions::HookContextLoadError => error
   puts error
   puts 'Are you running an old version of Overcommit?'
   exit 69 # EX_UNAVAILABLE
+rescue Overcommit::Exceptions::HookSetupFailed => error
+  puts error
+  exit 74 # EX_IOERR
 rescue Overcommit::Exceptions::HookCancelled
   puts 'You cancelled the hook run'
   exit 1