Fix bad rubygems binstub + locked bundler behaviorfix_rubygems_binstub_and_locked_version

When running a rubygems bundler binstub with lock file locked to a
non-installed bundler version, one would get the cryptic error message:

```
can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)
```

where one tends to think... What? How is it not found if I just run
it?!

2 files changed, 76 insertions, 0 deletions

diff --git a/spec/lock/lockfile_bundler_1_spec.rb b/spec/lock/lockfile_bundler_1_spec.rb
index a8615d4c89..54fa4b10ab 100644
--- a/spec/lock/lockfile_bundler_1_spec.rb
+++ b/spec/lock/lockfile_bundler_1_spec.rb
@@ -201,6 +201,44 @@ RSpec.describe "the lockfile format", :bundler => "< 2" do
     G
   end
 
+  it "outputs a warning if the current is older than lockfile's bundler version and using a rubygems binstub", :rubygems => "> 2.7.7" do
+    lockfile <<-L
+      GEM
+        remote: file://localhost#{gem_repo1}/
+        specs:
+
+      PLATFORMS
+        ruby
+
+      DEPENDENCIES
+
+      BUNDLED WITH
+         9999
+    L
+
+    gemfile <<-G
+      source "file://localhost#{gem_repo1}"
+    G
+
+    File.open("bundle", "w") do |f|
+      f.puts("#!/usr/bin/ruby")
+      f.puts('load Gem.activate_bin_path("bundler", "bundle", ">= 0.a")')
+    end
+
+    FileUtils.chmod(0o755, "bundle")
+
+    sys_exec "./bundle --version"
+    warning_messages = [
+      "Could not find 'bundler' (9999) required by your #{bundled_app("Gemfile.lock")}",
+      "To update to the lastest version installed on your system, run `bundle update --bundler`.",
+      "To install the missing version, run `gem install bundler:9999`",
+    ]
+
+    warning_messages.each do |message|
+      expect(out).to include(message)
+    end
+  end
+
   it "errors if the current is a major version older than lockfile's bundler version" do
     lockfile <<-L
       GEM
diff --git a/spec/lock/lockfile_spec.rb b/spec/lock/lockfile_spec.rb
index 53c832445f..f2ec869cc9 100644
--- a/spec/lock/lockfile_spec.rb
+++ b/spec/lock/lockfile_spec.rb
@@ -200,6 +200,44 @@ RSpec.describe "the lockfile format", :bundler => "2" do
     G
   end
 
+  it "outputs a warning if the current is older than lockfile's bundler version and using a rubygems binstub", :rubygems => "> 2.7.7" do
+    lockfile <<-L
+      GEM
+        remote: file://localhost#{gem_repo1}/
+        specs:
+
+      PLATFORMS
+        ruby
+
+      DEPENDENCIES
+
+      BUNDLED WITH
+         9999
+    L
+
+    gemfile <<-G
+      source "file://localhost#{gem_repo1}"
+    G
+
+    File.open("bundle", "w") do |f|
+      f.puts("#!/usr/bin/ruby")
+      f.puts('load Gem.activate_bin_path("bundler", "bundle", ">= 0.a")')
+    end
+
+    FileUtils.chmod(0o755, "bundle")
+
+    sys_exec "./bundle --version"
+    warning_messages = [
+      "Could not find 'bundler' (9999) required by your #{bundled_app("Gemfile.lock")}",
+      "To update to the lastest version installed on your system, run `bundle update --bundler`.",
+      "To install the missing version, run `gem install bundler:9999`",
+    ]
+
+    warning_messages.each do |message|
+      expect(out).to include(message)
+    end
+  end
+
   it "errors if the current is a major version older than lockfile's bundler version" do
     lockfile <<-L
       GEM