Include the currently active GC in RUBY_DESCRIPTION

This will add +MOD_GC to the version string and Ruby description when
Ruby is compiled with shared gc support.

When shared GC support is compiled in and a GC module has been loaded
using RUBY_GC_LIBRARY, the version string will include the name of
the currently active GC as reported by the rb_gc_active_gc_name function
in the form

+MOD_GC[gc_name]

[Feature #20794]

common.mk

@@ -19555,6 +19555,7 @@ version.$(OBJEXT): $(CCAN_DIR)/str/str.h
 version.$(OBJEXT): $(hdrdir)/ruby.h
 version.$(OBJEXT): $(hdrdir)/ruby/ruby.h
 version.$(OBJEXT): $(hdrdir)/ruby/version.h
+version.$(OBJEXT): $(top_srcdir)/gc/gc.h
 version.$(OBJEXT): $(top_srcdir)/internal/array.h
 version.$(OBJEXT): $(top_srcdir)/internal/basic_operators.h
 version.$(OBJEXT): $(top_srcdir)/internal/cmdlineopt.h

gc.c

@@ -562,6 +562,8 @@ rb_gc_guarded_ptr_val(volatile VALUE *ptr, VALUE val)
 static const char *obj_type_name(VALUE obj);
 #define RB_AMALGAMATED_DEFAULT_GC
 #include "gc/default.c"
+static int external_gc_loaded = FALSE;
+
 
 #if USE_SHARED_GC && !defined(HAVE_DLOPEN)
 # error "Shared GC requires dlopen"
@@ -696,6 +698,7 @@ ruby_external_gc_init(void)
             fprintf(stderr, "ruby_external_gc_init: Shared library %s cannot be opened: %s\n", gc_so_path, dlerror());
             exit(1);
         }
+        external_gc_loaded = TRUE;
     }
 
     rb_gc_function_map_t gc_functions;
@@ -2767,10 +2770,26 @@ rb_gc_copy_attributes(VALUE dest, VALUE obj)
     rb_gc_impl_copy_attributes(rb_gc_get_objspace(), dest, obj);
 }
 
+int
+rb_gc_external_gc_loaded_p(void) {
+    return external_gc_loaded;
+}
+
 const char *
 rb_gc_active_gc_name(void)
 {
-    return rb_gc_impl_active_gc_name();
+    const char *gc_name = rb_gc_impl_active_gc_name();
+    if (strlen(gc_name) > RB_GC_MAX_NAME_LEN) {
+        char *truncated_gc_name = ruby_xmalloc(RB_GC_MAX_NAME_LEN + 1);
+
+        rb_warn("GC module %s has a name larger than %d chars, it will be truncated\n",
+            gc_name, RB_GC_MAX_NAME_LEN);
+
+        strncpy(truncated_gc_name, gc_name, RB_GC_MAX_NAME_LEN);
+        return (const char *)truncated_gc_name;
+    }
+    return gc_name;
+
 }
 
 // TODO: rearchitect this function to work for a generic GC

internal/gc.h

@@ -234,6 +234,7 @@ size_t rb_gc_obj_slot_size(VALUE obj);
 
 VALUE rb_gc_disable_no_rest(void);
 
+#define RB_GC_MAX_NAME_LEN 20
 
 /* gc.c (export) */
 const char *rb_objspace_data_type_name(VALUE obj);
@@ -248,6 +249,9 @@ void *ruby_sized_xrealloc(void *ptr, size_t new_size, size_t old_size) RUBY_ATTR
 void *ruby_sized_xrealloc2(void *ptr, size_t new_count, size_t element_size, size_t old_count) RUBY_ATTR_RETURNS_NONNULL RUBY_ATTR_ALLOC_SIZE((2, 3));
 void ruby_sized_xfree(void *x, size_t size);
 
+const char * rb_gc_active_gc_name(void);
+int rb_gc_external_gc_loaded_p(void);
+
 #if USE_SHARED_GC
 void ruby_load_external_gc_from_argv(int argc, char **argv);
 #endif

spec/ruby/command_line/dash_v_spec.rb

@@ -9,6 +9,7 @@ describe "The -v command line option" do
       ruby_exe(nil, args: '-v').sub("+PRISM ", "").should include(RUBY_DESCRIPTION.sub("+PRISM ", ""))
     end unless (defined?(RubyVM::YJIT) && RubyVM::YJIT.enabled?) ||
                (defined?(RubyVM::RJIT) && RubyVM::RJIT.enabled?) ||
+               (ENV['RUBY_GC_LIBRARY'] && ENV['RUBY_GC_LIBRARY'].length > 0) ||
                (ENV['RUBY_MN_THREADS'] == '1')
   end
 end

spec/ruby/command_line/rubyopt_spec.rb

@@ -25,12 +25,12 @@ describe "Processing RUBYOPT" do
   guard -> { RbConfig::CONFIG["CROSS_COMPILING"] != "yes" } do
     it "prints the version number for '-v'" do
       ENV["RUBYOPT"] = '-v'
-      ruby_exe("").sub("+PRISM ", "")[/\A.*/].should == RUBY_DESCRIPTION.sub("+PRISM ", "")
+      ruby_exe("").sub("+PRISM ", "").sub(/\+GC(\[\w+\]\s|\s)?/, "")[/\A.*/].should == RUBY_DESCRIPTION.sub("+PRISM ", "").sub(/\+GC(\[\w+\]\s|\s)?/, "")
     end
 
     it "ignores whitespace around the option" do
       ENV["RUBYOPT"] = ' -v '
-      ruby_exe("").sub("+PRISM ", "")[/\A.*/].should == RUBY_DESCRIPTION.sub("+PRISM ", "")
+      ruby_exe("").sub("+PRISM ", "").sub(/\+GC(\[\w+\]\s|\s)?/, "")[/\A.*/].should == RUBY_DESCRIPTION.sub("+PRISM ", "").sub(/\+GC(\[\w+\]\s|\s)?/, "")
     end
   end
 

test/ruby/test_rubyoptions.rb

@@ -176,7 +176,7 @@ class TestRubyOptions < Test::Unit::TestCase
   VERSION_PATTERN_WITH_RJIT =
     case RUBY_ENGINE
     when 'ruby'
-      /^ruby #{q[RUBY_VERSION]}(?:[p ]|dev|rc).*? \+RJIT (\+MN )?(\+PRISM )?\[#{q[RUBY_PLATFORM]}\]$/
+      /^ruby #{q[RUBY_VERSION]}(?:[p ]|dev|rc).*? \+RJIT (\+MN )?(\+PRISM )?(\+GC)?(\[\w+\]\s|\s)?\[#{q[RUBY_PLATFORM]}\]$/
     else
       VERSION_PATTERN
     end
@@ -307,6 +307,16 @@ class TestRubyOptions < Test::Unit::TestCase
     end
   end
 
+  def test_enabled_gc
+    omit unless /linux|darwin/ =~ RUBY_PLATFORM
+
+    if RbConfig::CONFIG['shared_gc_dir'].length > 0
+      assert_match(/\+GC/, RUBY_DESCRIPTION)
+    else
+      assert_no_match(/\+GC/, RUBY_DESCRIPTION)
+    end
+  end
+
   def test_parser_flag
     assert_in_out_err(%w(--parser=prism -e) + ["puts :hi"], "", %w(hi), [])
     assert_in_out_err(%w(--parser=prism --dump=parsetree -e _=:hi), "", /"hi"/, [])

version.c

@@ -11,6 +11,7 @@
 
 #include "internal/cmdlineopt.h"
 #include "internal/parse.h"
+#include "internal/gc.h"
 #include "ruby/ruby.h"
 #include "version.h"
 #include "vm_core.h"
@@ -61,6 +62,11 @@ const int ruby_api_version[] = {
 #else
 #define YJIT_DESCRIPTION " +YJIT"
 #endif
+#if USE_SHARED_GC
+#define GC_DESCRIPTION " +GC"
+#else
+#define GC_DESCRIPTION ""
+#endif
 const char ruby_version[] = RUBY_VERSION;
 const char ruby_revision[] = RUBY_FULL_REVISION;
 const char ruby_release_date[] = RUBY_RELEASE_DATE;
@@ -167,6 +173,14 @@ define_ruby_description(const char *const jit_opt)
         + rb_strlen_lit(YJIT_DESCRIPTION)
         + rb_strlen_lit(" +MN")
         + rb_strlen_lit(" +PRISM")
+#if USE_SHARED_GC
+        + rb_strlen_lit(GC_DESCRIPTION)
+        // Assume the active GC name can not be longer than 20 chars
+        // so that we don't have to use strlen and remove the static
+        // qualifier from desc.
+        + RB_GC_MAX_NAME_LEN + 3
+#endif
+
     ];
 
     int n = ruby_description_opt_point;
@@ -176,6 +190,14 @@ define_ruby_description(const char *const jit_opt)
     RUBY_ASSERT(n <= ruby_description_opt_point + (int)rb_strlen_lit(YJIT_DESCRIPTION));
     if (ruby_mn_threads_enabled) append(" +MN");
     if (rb_ruby_prism_p()) append(" +PRISM");
+#if USE_SHARED_GC
+    append(GC_DESCRIPTION);
+    if (rb_gc_external_gc_loaded_p()) {
+        append("[");
+        append(rb_gc_active_gc_name());
+        append("]");
+    }
+#endif
     append(ruby_description + ruby_description_opt_point);
 # undef append