update: always reset to origin/master.

Do a reset to `origin/master` and then stash but don't pop the stash
after running update (unless you were on a branch). This may be mildly
more annoying for Homebrew developers but means it's easier for our
users who don't understand Git (and particularly when they don't
understand that every tap is a separate Git repository).

Closes Homebrew/homebrew#45825.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

2 files changed, 37 insertions, 22 deletions

diff --git a/Library/Homebrew/cmd/update.rb b/Library/Homebrew/cmd/update.rb
index 10b4da661..6ee2726a9 100644
--- a/Library/Homebrew/cmd/update.rb
+++ b/Library/Homebrew/cmd/update.rb
@@ -203,15 +203,6 @@ class Updater
   end
 
   def pull!(options = {})
-    unless system "git", "diff", "--quiet"
-      if ARGV.verbose?
-        puts "Stashing your changes:"
-        system "git", "status", "--short", "--untracked-files"
-      end
-      safe_system "git", "stash", "save", "--include-untracked", *@quiet_args
-      @stashed = true
-    end
-
     # The upstream repository's default branch may not be master;
     # check refs/remotes/origin/HEAD to see what the default
     # origin branch name is, and use that. If not set, fall back to "master".
@@ -228,6 +219,16 @@ class Updater
       @initial_branch = ""
     end
 
+    unless `git status --untracked-files=all --porcelain 2>/dev/null`.chomp.empty?
+      if ARGV.verbose?
+        puts "Stashing uncommitted changes to #{repository}."
+        system "git", "status", "--short", "--untracked-files=all"
+      end
+      safe_system "git", "stash", "save", "--include-untracked", *@quiet_args
+      safe_system "git", "reset", "--hard", *@quiet_args
+      @stashed = true
+    end
+
     # Used for testing purposes, e.g., for testing formula migration after
     # renaming it in the currently checked-out branch. To test run
     # "brew update --simulate-from-current-branch"
@@ -243,7 +244,7 @@ class Updater
     end
 
     if @initial_branch != @upstream_branch && !@initial_branch.empty?
-      safe_system "git", "checkout", @upstream_branch, *@quiet_args
+      safe_system "git", "checkout", "--force", "-B", @upstream_branch, "origin/#{@upstream_branch}", *@quiet_args
     end
 
     @initial_revision = read_current_revision
@@ -263,18 +264,29 @@ class Updater
 
     @current_revision = read_current_revision
 
-    if @initial_branch != "master" && !@initial_branch.empty?
+    if @initial_branch != @upstream_branch && !@initial_branch.empty?
       safe_system "git", "checkout", @initial_branch, *@quiet_args
+      pop_stash
+    else
+      pop_stash_message
     end
+  end
 
-    if @stashed
-      safe_system "git", "stash", "pop", *@quiet_args
-      if ARGV.verbose?
-        puts "Restored your changes:"
-        system "git", "status", "--short", "--untracked-files"
-      end
-      @stashed = false
+  def pop_stash
+    return unless @stashed
+    safe_system "git", "stash", "pop", *@quiet_args
+    if ARGV.verbose?
+      puts "Restoring your stashed changes to #{repository}:"
+      system "git", "status", "--short", "--untracked-files"
     end
+    @stashed = false
+  end
+
+  def pop_stash_message
+    return unless @stashed
+    puts "To restore the stashed changes to #{repository} run:"
+    puts "  `cd #{repository} && git stash pop`"
+    @stashed = false
   end
 
   def reset_on_interrupt
@@ -282,9 +294,12 @@ class Updater
   ensure
     if $?.signaled? && $?.termsig == 2 # SIGINT
       safe_system "git", "checkout", @initial_branch unless @initial_branch.empty?
-      safe_system "git", "reset", "--hard", @initial_revision
-      safe_system "git", "stash", "pop", *@quiet_args if @stashed
-      @stashed = false
+      safe_system "git", "reset", "--hard", @initial_revision, *@quiet_args
+      if @initial_branch
+        pop_stash
+      else
+        pop_stash_message
+      end
     end
   end
 
diff --git a/Library/Homebrew/test/test_updater.rb b/Library/Homebrew/test/test_updater.rb
index 20d26e6e9..16efdaa1d 100644
--- a/Library/Homebrew/test/test_updater.rb
+++ b/Library/Homebrew/test/test_updater.rb
@@ -57,9 +57,9 @@ class UpdaterTests < Homebrew::TestCase
     Formulary.stubs(:factory).returns(stub(:pkg_version => "1.0"))
     FormulaVersions.stubs(:new).returns(stub(:formula_at_revision => "2.0"))
     @updater.diff = fixture(fixture_name)
-    @updater.in_repo_expect("git diff --quiet", true)
     @updater.in_repo_expect("git symbolic-ref refs/remotes/origin/HEAD 2>/dev/null", "refs/remotes/origin/master")
     @updater.in_repo_expect("git symbolic-ref --short HEAD 2>/dev/null", "master")
+    @updater.in_repo_expect("git status --untracked-files=all --porcelain 2>/dev/null", "")
     @updater.in_repo_expect("git rev-parse -q --verify HEAD", "1234abcd")
     @updater.in_repo_expect("git config core.autocrlf false")
     @updater.in_repo_expect("git pull --ff --no-rebase --quiet origin refs/heads/master:refs/remotes/origin/master")