cdhash_cmp: can take rational literals

Rational literals are those integers suffixed with `r`.  They tend to
be a part of more complex expressions like `123/456r`, but in theory
they can live alone.  When such "bare" rational literals are passed to
case-when branch, we have to take care of them.  Fixes [Bug #17854]

common.mk

@@ -2807,6 +2807,7 @@ compile.$(OBJEXT): $(top_srcdir)/internal/hash.h
 compile.$(OBJEXT): $(top_srcdir)/internal/imemo.h
 compile.$(OBJEXT): $(top_srcdir)/internal/numeric.h
 compile.$(OBJEXT): $(top_srcdir)/internal/object.h
+compile.$(OBJEXT): $(top_srcdir)/internal/rational.h
 compile.$(OBJEXT): $(top_srcdir)/internal/re.h
 compile.$(OBJEXT): $(top_srcdir)/internal/serial.h
 compile.$(OBJEXT): $(top_srcdir)/internal/static_assert.h

compile.c

@@ -28,6 +28,7 @@
 #include "internal/hash.h"
 #include "internal/numeric.h"
 #include "internal/object.h"
+#include "internal/rational.h"
 #include "internal/re.h"
 #include "internal/symbol.h"
 #include "internal/thread.h"
@@ -2004,6 +2005,10 @@ cdhash_cmp(VALUE val, VALUE lit)
     else if (tlit == T_FLOAT) {
         return rb_float_cmp(lit, val);
     }
+    else if (tlit ==  T_RATIONAL) {
+        /* Rational literals don't have fractions. */
+        return cdhash_cmp(val, rb_rational_num(lit));
+    }
     else {
         UNREACHABLE_RETURN(-1);
     }
@@ -2022,6 +2027,8 @@ cdhash_hash(VALUE a)
         return FIX2LONG(rb_big_hash(a));
       case T_FLOAT:
         return rb_dbl_long_hash(RFLOAT_VALUE(a));
+      case T_RATIONAL:
+        return rb_rational_hash(a);
       default:
         UNREACHABLE_RETURN(0);
     }

internal/rational.h

@@ -33,6 +33,7 @@ VALUE rb_rational_div(VALUE self, VALUE other);
 VALUE rb_lcm(VALUE x, VALUE y);
 VALUE rb_rational_reciprocal(VALUE x);
 VALUE rb_cstr_to_rat(const char *, int);
+VALUE rb_rational_hash(VALUE self);
 VALUE rb_rational_abs(VALUE self);
 VALUE rb_rational_cmp(VALUE self, VALUE other);
 VALUE rb_rational_pow(VALUE self, VALUE other);

rational.c

@@ -1742,8 +1742,8 @@ nurat_rationalize(int argc, VALUE *argv, VALUE self)
 }
 
 /* :nodoc: */
-static VALUE
+st_index_t
-nurat_hash(VALUE self)
+rb_rational_hash(VALUE self)
 {
     st_index_t v, h[2];
     VALUE n;
@@ -1754,9 +1754,16 @@ nurat_hash(VALUE self)
     n = rb_hash(dat->den);
     h[1] = NUM2LONG(n);
     v = rb_memhash(h, sizeof(h));
-    return ST2FIX(v);
+    return v;
 }
 
+static VALUE
+nurat_hash(VALUE self)
+{
+    return ST2FIX(rb_rational_hash(self));
+}
+
+
 static VALUE
 f_format(VALUE self, VALUE (*func)(VALUE))
 {

test/ruby/test_rational.rb

@@ -830,6 +830,13 @@ class Rational_Test < Test::Unit::TestCase
     assert_raise(ZeroDivisionError) {Rational("1/0")}
   end
 
+  def test_cdhash
+    assert_separately([], <<-RUBY)
+      n = case 1 when 2r then false else true end
+      assert_equal(n, true, '[ruby-core:103759] [Bug #17854]')
+    RUBY
+  end
+
   def test_Rational_with_invalid_exception
     assert_raise(ArgumentError) {
       Rational("1/1", exception: 1)