Merge #7149

7149: Fix bundle update crash r=deivid-rodriguez a=deivid-rodriguez

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

The problem was that I introduced a regression with #6329. When running `bundle update <gem>`, where `<gem>` is included in the Gemfile, but it's for another platform from the current one, `bundle` would crash with the following error:

```
NoMethodError: undefined method `source' for nil:NilClass
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli/update.rb:86:in `block in run'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli/update.rb:78:in `each'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli/update.rb:78:in `run'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli.rb:280:in `block in update'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/settings.rb:129:in `temporary'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli.rb:279:in `update'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/vendor/thor/lib/thor/invocation.rb:126:in `invoke_command'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/vendor/thor/lib/thor.rb:387:in `dispatch'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli.rb:26:in `dispatch'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/vendor/thor/lib/thor/base.rb:466:in `start'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/cli.rb:17:in `start'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/exe/bundle:21:in `block in <top (required)>'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/lib/bundler/friendly_errors.rb:123:in `with_friendly_errors'
  /home/deivid/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/bundler-2.1.0.pre.1/exe/bundle:13:in `<top (required)>'
  /home/deivid/.rbenv/versions/2.6.3/bin/bundle:23:in `load'
  /home/deivid/.rbenv/versions/2.6.3/bin/bundle:23:in `<main>'
```


### What was your diagnosis of the problem?

My diagnosis was that we can't always rely on the spec being updated not being `nil` in the definition. It can be `nil` for gems in excluded groups, or for gems included only for platforms different from the current one.

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

My fix is to handle this case and show a proper error.

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

I chose this fix because it's user friendly.


Co-authored-by: David Rodríguez <deivid.rodriguez@riseup.net>

lib/bundler/cli/update.rb

@@ -60,8 +60,8 @@ def run
       Bundler.definition.validate_runtime!
 
       if locked_gems = Bundler.definition.locked_gems
-        previous_locked_specs = locked_gems.specs.reduce({}) do |h, s|
-          h[s.name] = { :version => s.version, :source => s.source.to_s }
+        previous_locked_info = locked_gems.specs.reduce({}) do |h, s|
+          h[s.name] = { :spec => s, :version => s.version, :source => s.source.to_s }
           h
         end
       end
@@ -76,17 +76,26 @@ def run
 
       if locked_gems
         gems.each do |name|
-          locked_spec = previous_locked_specs[name]
-          next unless locked_spec
-          locked_source = locked_spec[:source]
-          locked_version = locked_spec[:version]
+          locked_info = previous_locked_info[name]
+          next unless locked_info
+
+          locked_spec = locked_info[:spec]
           new_spec = Bundler.definition.specs[name].first
+          unless new_spec
+            if Bundler.rubygems.platforms.none? {|p| locked_spec.match_platform(p) }
+              Bundler.ui.warn "Bundler attempted to update #{name} but it was not considered because it is for a different platform from the current one"
+            end
+
+            next
+          end
+
+          locked_source = locked_info[:source]
           new_source = new_spec.source.to_s
-          new_version = new_spec.version
           next if locked_source != new_source
-          if !new_version
-            Bundler.ui.warn "Bundler attempted to update #{name} but it was removed from the bundle"
-          elsif new_version < locked_version
+
+          new_version = new_spec.version
+          locked_version = locked_info[:version]
+          if new_version < locked_version
             Bundler.ui.warn "Note: #{name} version regressed from #{locked_version} to #{new_version}"
           elsif new_version == locked_version
             Bundler.ui.warn "Bundler attempted to update #{name} but its version stayed the same"

spec/commands/update_spec.rb

@@ -563,6 +563,41 @@
       expect(the_bundle).to include_gem "a 1.1"
     end
   end
+
+  context "when the dependency is for a different platform" do
+    before do
+      build_repo4 do
+        build_gem("a", "0.9") {|s| s.platform = "java" }
+        build_gem("a", "1.1") {|s| s.platform = "java" }
+      end
+
+      gemfile <<-G
+        source "file://#{gem_repo4}"
+        gem "a", platform: :jruby
+      G
+
+      lockfile <<-L
+        GEM
+          remote: file://#{gem_repo4}
+          specs:
+            a (0.9-java)
+
+        PLATFORMS
+          java
+
+        DEPENDENCIES
+          a
+      L
+
+      simulate_platform linux
+    end
+
+    it "is not updated because it is not actually included in the bundle" do
+      bundle! "update a"
+      expect(last_command.stdboth).to include "Bundler attempted to update a but it was not considered because it is for a different platform from the current one"
+      expect(the_bundle).to_not include_gem "a"
+    end
+  end
 end
 
 RSpec.describe "bundle update without a Gemfile.lock" do