[ruby/rubygems] Raise error when gem contains capital letters

The problem is described in https://github.com/rubygems/rubygems/issues/5431
The guide ( https://guides.rubygems.org/name-your-gem/ ) says
> DON’T USE UPPERCASE LETTERS
so `bundle gem` command should respect it.

https://github.com/ruby/rubygems/commit/ea1b1e2209

2 files changed, 7 insertions, 2 deletions

diff --git a/lib/bundler/cli/gem.rb b/lib/bundler/cli/gem.rb
index 236ce530ec..783a833e77 100644
--- a/lib/bundler/cli/gem.rb
+++ b/lib/bundler/cli/gem.rb
@@ -430,8 +430,8 @@ module Bundler
     end
 
     def ensure_safe_gem_name(name, constant_array)
-      if /^\d/.match?(name)
-        Bundler.ui.error "Invalid gem name #{name} Please give a name which does not start with numbers."
+      if /(^\d)|[A-Z]/.match?(name)
+        Bundler.ui.error "Invalid gem name #{name} Please give a name which does not start with numbers nor include capital letters."
         exit 1
       end
 
diff --git a/spec/bundler/commands/newgem_spec.rb b/spec/bundler/commands/newgem_spec.rb
index 06c226f9e5..32f5e790af 100644
--- a/spec/bundler/commands/newgem_spec.rb
+++ b/spec/bundler/commands/newgem_spec.rb
@@ -1982,6 +1982,11 @@ Usage: "bundle gem NAME [OPTIONS]"
       it { expect(err).to include("Invalid gem name #{subject}") }
     end
 
+    context "including capital letter" do
+      subject { "CAPITAL" }
+      it { expect(err).to include("Invalid gem name #{subject}") }
+    end
+
     context "starting with an existing const name" do
       subject { "gem-somenewconstantname" }
       it { expect(err).not_to include("Invalid gem name #{subject}") }