core: lock prerelease gems

CHANGELOG.md

@@ -18,6 +18,8 @@ BUG FIXES:
       a string and not a symbol. [GH-3349]
   - core: Converting to cygwin path works for folders with spaces. [GH-3304]
   - core: Can add boxes with spaces in their path. [GH-3306]
+  - core: Prerelease plugins installed are locked to that prerelease
+      version. [GH-3301]
   - commands/box: Show versions when listing. [GH-3316]
   - commands/status: Machine readable output contains the target. [GH-3218]
   - guests/arch: Reload udev rules after network change. [GH-3322]

lib/vagrant/plugin/manager.rb

@@ -72,9 +72,10 @@ module Vagrant
           install_lambda.call
         end
 
-        # If the version constraint is just a specific (non prerelease) version, don't
-        # store the constraint.
-        if opts[:version] && opts[:version] =~ /^\d/ && !Gem::Requirement.parse(opts[:version])[1].prerelease?
+        # If the version constraint is just a specific version, don't
+        # store the constraint. However, if it is a prerelease version,
+        # we DO store the constraint to avoid Bundler updating it.
+        if opts[:version] && opts[:version] =~ /^\d/ && opts[:version] !~ /[a-z]/i
           opts.delete(:version)
         end