RUBY-2870 Test driver against bson master and 4-stable

.evergreen/config.yml

@@ -756,7 +756,11 @@ axes:
         display_name: min
         variables:
           BSON: min
-
+      - id: 4-stable
+        display_name: 4-stable
+        variables:
+          BSON: 4-stable
+
   - id: storage-engine
     display_name: Storage Engine
     values:

.evergreen/functions.sh

@@ -43,7 +43,10 @@ set_env_vars() {
   if test "$BSON" = min; then
     export BUNDLE_GEMFILE=gemfiles/bson_min.gemfile
   elif test "$BSON" = master; then
+    export MONGO_RUBY_DRIVER_BSON_MASTER=1
     export BUNDLE_GEMFILE=gemfiles/bson_master.gemfile
+  elif test "$BSON" = 4-stable; then
+    export BUNDLE_GEMFILE=gemfiles/bson_4-stable.gemfile
   elif test "$COMPRESSOR" = snappy; then
     export BUNDLE_GEMFILE=gemfiles/snappy_compression.gemfile
   elif test "$COMPRESSOR" = zstd; then
@@ -59,17 +62,18 @@ set_env_vars() {
 bundle_install() {
   args=--quiet
 
-  if test "$BSON" = master; then
+  if test "$BSON" = master || test "$BSON" = 4-stable; then
     # In Docker bson is installed in the image, remove it if we need bson master.
     gem uni bson || true
   fi
 
   # On JRuby we can test against bson master but not in a conventional way.
   # See https://jira.mongodb.org/browse/RUBY-2156
-  if echo $RVM_RUBY |grep -q jruby && test "$BSON" = master; then
+  if echo $RVM_RUBY |grep -q jruby && (test "$BSON" = master || test "$BSON" = 4-stable); then
     unset BUNDLE_GEMFILE
     git clone https://github.com/mongodb/bson-ruby
     (cd bson-ruby &&
+      git checkout "origin/$BSON" &&
       bundle install &&
       rake compile &&
       gem build *.gemspec &&

gemfiles/bson_4-stable.gemfile

@@ -0,0 +1,8 @@
+source "https://rubygems.org"
+gemspec path: '..'
+
+gem 'bson', git: 'https://github.com/mongodb/bson-ruby', branch: '4-stable'
+
+require_relative './standard'
+
+standard_dependencies

gemfiles/bson_master.gemfile

@@ -1,7 +1,7 @@
 source "https://rubygems.org"
 gemspec path: '..'
 
-gem 'bson', git: 'https://github.com/mongodb/bson-ruby', branch: '4-stable'
+gem 'bson', git: 'https://github.com/mongodb/bson-ruby', branch: 'master'
 
 require_relative './standard'
 

mongo.gemspec

@@ -37,6 +37,12 @@ Gem::Specification.new do |s|
   s.bindir            = 'bin'
 
   s.required_ruby_version = ">= 2.5"
-
-  s.add_dependency 'bson', '>=4.13.0', '<5.0.0'
+
+  # For testing driver against bson master we need to depend on bson < 6.0.0 
+  # but in release version we want to depend on bson < 5.0.0.
+  if %w(1 yes true).include?(ENV['MONGO_RUBY_DRIVER_BSON_MASTER'])
+    s.add_dependency 'bson', '>=4.13.0', '<6.0.0'
+  else 
+    s.add_dependency 'bson', '>=4.13.0', '<5.0.0'
+  end
 end