Add a CI check for ABI compatibility and only increment ABI version w…

…hen needed

* Fixes oracle#2284

doc/contributor/updating-ruby.md

@@ -161,6 +161,7 @@ In a separate commit, update all of these:
 * Grep for the old version with `git grep -F x.y.z`
 * If `tool/id.def` or `lib/cext/include/truffleruby/internal/id.h` has changed, `jt build core-symbols` and check for correctness.
 * Update the list of `:next` specs and change the "next version" in `spec/truffleruby.mspec`.
+* Reset `lib/cext/ABI_version.txt` and `lib/cext/ABI_check.txt` to `1` if `RUBY_VERSION` was updated.
 
 ## Last step
 

lib/cext/ABI_check.txt

@@ -0,0 +1 @@
+1

lib/cext/ABI_version.txt

@@ -0,0 +1 @@
+1

lib/truffle/rbconfig.rb

@@ -51,9 +51,7 @@ module RbConfig
   ruby_install_name = 'truffleruby'
   ruby_base_name = 'ruby'
 
-  # The full TruffleRuby version, so C extensions from one TruffleRuby version
-  # are not reused with another TruffleRuby version.
-  ruby_abi_version = RUBY_ENGINE_VERSION
+  ruby_abi_version = Truffle::GemUtil.abi_version
 
   arch = "#{host_cpu}-#{host_os}"
   libs = ''

mx.truffleruby/suite.py

@@ -473,6 +473,7 @@
                 ],
                 "lib/cext/": [
                     "file:lib/cext/*.rb",
+                    "file:lib/cext/ABI_version.txt",
                     "dependency:org.truffleruby.cext/src/main/c/truffleposix/<lib:truffleposix>",
                     "dependency:org.truffleruby.cext/src/main/c/cext/<lib:truffleruby>",
                     "dependency:org.truffleruby.rubysignal",

spec/truffle/identity_spec.rb

@@ -67,8 +67,8 @@
     RbConfig::CONFIG['RUBY_INSTALL_NAME'].should == 'truffleruby'
   end
 
-  it "RbConfig::CONFIG['ruby_version'] is the ABI version and matches RUBY_ENGINE_VERSION" do
-    RbConfig::CONFIG['ruby_version'].should == RUBY_ENGINE_VERSION
+  it "RbConfig::CONFIG['ruby_version'] is the ABI version and starts with RUBY_VERSION and has an extra component" do
+    RbConfig::CONFIG['ruby_version'].should =~ /\A#{Regexp.escape RUBY_VERSION}\.\d+\z/
   end
 
   it "RbConfig::CONFIG['RUBY_BASE_NAME'] is 'ruby'" do

src/main/c/Makefile

@@ -65,7 +65,7 @@ $(TRUFFLE_POSIX): truffleposix/Makefile truffleposix/truffleposix.c
 cext/Makefile: cext/extconf.rb $(BASIC_EXTCONF_DEPS)
 	$(Q) cd cext && $(RUBY) extconf.rb || $(IF_EXTCONF_FAIL)
 
-$(LIBTRUFFLERUBY): cext/Makefile cext/*.c
+$(LIBTRUFFLERUBY): cext/Makefile cext/*.c cext/*.h
 	$(Q) cd cext && $(MAKE)
 
 # openssl

src/main/ruby/truffleruby/core/post.rb

@@ -111,7 +111,7 @@ def p(*a)
     # Does not exist but it's used by rubygems to determine index where to insert gem lib directories, as a result
     # paths supplied by -I will stay before gem lib directories. See Gem.load_path_insert_index in rubygems.rb.
     # Must be kept in sync with the value of RbConfig::CONFIG['sitelibdir'].
-    $LOAD_PATH.push "#{ruby_home}/lib/ruby/site_ruby/#{RUBY_ENGINE_VERSION}"
+    $LOAD_PATH.push "#{ruby_home}/lib/ruby/site_ruby/#{Truffle::GemUtil.abi_version}"
 
     $LOAD_PATH.push "#{ruby_home}/lib/truffle"
     $LOAD_PATH.push "#{ruby_home}/lib/mri"

src/main/ruby/truffleruby/core/truffle/gem_util.rb

@@ -122,14 +122,19 @@ def self.gem_paths
       if gem_path = ENV['GEM_PATH']
         paths.concat gem_path.split(File::PATH_SEPARATOR)
       else
-        user_dir = "#{Dir.home}/.gem/truffleruby/#{RUBY_ENGINE_VERSION}"
+        user_dir = "#{Dir.home}/.gem/truffleruby/#{abi_version}"
         paths << user_dir
       end
 
       paths.map { |path| expand(path) }.uniq
     end
   end
 
+  def self.abi_version
+    abi_version = File.read("#{Truffle::Boot.ruby_home}/lib/cext/ABI_version.txt").strip
+    "#{RUBY_VERSION}.#{abi_version}"
+  end
+
   def self.expand(path)
     if File.directory?(path)
       File.realpath(path)

tool/jt.rb

@@ -2659,7 +2659,7 @@ def lint(*args)
     args.shift if fast
 
     if fast and compare_to = args.shift
-      changed_files = `git diff --cached --name-only #{compare_to}`.lines.map(&:chomp)
+      changed_files = changed_files(compare_to)
       changed = {}
       changed_files.each do |file|
         changed.fetch(File.extname(file)) { |k| changed[k] = [] } << file
@@ -2690,11 +2690,54 @@ def lint(*args)
       check_documentation
       check_documentation_urls
       check_license
+      check_abi
 
       check_source_files if ci?
     end
   end
 
+  ABI_VERSION_FILE = 'lib/cext/ABI_version.txt'
+  ABI_CHECK_FILE = 'lib/cext/ABI_check.txt'
+
+  def check_abi
+    # Check since the last commit at which ABI_CHECK_FILE or ABI_VERSION_FILE were modified
+    base_commit = `git log --format=%H #{ABI_VERSION_FILE} #{ABI_CHECK_FILE}`.chomp
+
+    changed_files = changed_files(base_commit)
+    # All files which can affect the ABI of libtruffleruby.so
+    abi_files = %w[
+      lib/truffle/rbconfig.rb
+      lib/mri/mkmf.rb
+      lib/cext/include/**/*.{h,hpp}
+      src/main/c/cext/extconf.rb
+      src/main/c/cext/*.{c,h}
+    ].flat_map { |pattern| Dir[pattern].sort }
+
+    changed_abi_files = changed_files & abi_files
+    unless changed_abi_files.empty?
+      puts 'These files have changed and might have affected the ABI:'
+      puts changed_abi_files
+      puts
+      if changed_files.include?(ABI_VERSION_FILE)
+        puts "#{ABI_VERSION_FILE} was updated to use a new ABI version"
+      elsif changed_files.include?(ABI_CHECK_FILE)
+        puts "#{ABI_CHECK_FILE} was updated, so ABI was marked as compatible"
+      else
+        puts 'Check the diff of this PR, and:'
+        puts "* if ABI has changed, then increment #{ABI_VERSION_FILE}"
+        puts "* if ABI has not changed, then increment #{ABI_CHECK_FILE}"
+        puts
+        puts 'Changing a macro, changing compilation flags, removing or adding a non-static function'
+        puts '(because e.g. mkmf have_func can depend on that) should all be considered ABI changes.'
+        abort
+      end
+    end
+  end
+
+  private def changed_files(base_commit)
+    `git diff --cached --name-only #{base_commit}`.lines.map(&:chomp)
+  end
+
   # Separate from lint as it needs to build
   def spotbugs
     mx 'ruby_spotbugs'