Auto merge of #5722 - bundler:seg-update-all-flag, r=indirect

Add `—all` flag to `bundle update`

### What was the end-user problem that led to this PR?

The problem was that some users would think they needed to run `bundle update` instead of `bundle install`, and we want such a (potentially) destructive action to require more explicit user approval.

### Was was your diagnosis of the problem?

My diagnosis was that `bundle update` shouldn't implicitly update _everything_ without an acknowledgement that it will do so.

### What is your fix for the problem, implemented in this PR?

My fix, based on https://github.com/bundler/bundler/pull/2646, it to require `bundle update --all` for the current `bundle update` behavior.

### Why did you choose this fix out of the possible options?

I chose this fix because it was already on 2-0-dev, courtesy of https://github.com/bundler/bundler-features/issues/18.

2 files changed, 16 insertions, 4 deletions

diff --git a/lib/bundler/cli/install.rb b/lib/bundler/cli/install.rb
index d57cad1e3f..f36ca94821 100644
--- a/lib/bundler/cli/install.rb
+++ b/lib/bundler/cli/install.rb
@@ -208,10 +208,11 @@ module Bundler
 
       Bundler.settings[:clean]               = options["clean"] if options["clean"]
 
-      Bundler.settings.without               = options[:without]
-      Bundler.settings.with                  = options[:with]
+      Bundler.settings.without               = options[:without] unless Bundler.settings.without == options[:without]
+      Bundler.settings.with                  = options[:with] unless Bundler.settings.with == options[:with]
 
-      Bundler.settings[:disable_shared_gems] = Bundler.settings[:path] ? true : nil
+      disable_shared_gems = Bundler.settings[:path] ? true : nil
+      Bundler.settings[:disable_shared_gems] = disable_shared_gems unless Bundler.settings[:disable_shared_gems] == disable_shared_gems
     end
 
     def warn_ambiguous_gems
diff --git a/lib/bundler/cli/update.rb b/lib/bundler/cli/update.rb
index df7524f004..9e4543668e 100644
--- a/lib/bundler/cli/update.rb
+++ b/lib/bundler/cli/update.rb
@@ -17,7 +17,18 @@ module Bundler
       sources = Array(options[:source])
       groups  = Array(options[:group]).map(&:to_sym)
 
-      if gems.empty? && sources.empty? && groups.empty? && !options[:ruby] && !options[:bundler]
+      full_update = gems.empty? && sources.empty? && groups.empty? && !options[:ruby] && !options[:bundler]
+
+      if full_update && !options[:all]
+        if Bundler.feature_flag.update_requires_all_flag?
+          raise InvalidOption, "To update everything, pass the `--all` flag."
+        end
+        SharedHelpers.major_deprecation "Pass --all to `bundle update` to update everything"
+      elsif !full_update && options[:all]
+        raise InvalidOption, "Cannot specify --all along with specific options."
+      end
+
+      if full_update
         # We're doing a full update
         Bundler.definition(true)
       else