Make Kernel#{Pathname,BigDecimal,Complex} return argument if given correct type

This is how Kernel#{Array,String,Float,Integer,Hash,Rational} work.
BigDecimal and Complex instances are always frozen, so this should
not cause backwards compatibility issues for those.  Pathname
instances are not frozen, so potentially this could cause backwards
compatibility issues by not returning a new object.

Based on a patch from Joshua Ballanco, some minor changes by me.

Fixes [Bug #7522]

6 files changed, 23 insertions, 0 deletions

diff --git a/complex.c b/complex.c
index ec60c00ed6..144a59d533 100644
--- a/complex.c
+++ b/complex.c
@@ -563,6 +563,9 @@ nucomp_f_complex(int argc, VALUE *argv, VALUE klass)
     if (!NIL_P(opts)) {
         raise = rb_opts_exception_p(opts, raise);
     }
+    if (argc > 0 && CLASS_OF(a1) == rb_cComplex && a2 == Qundef) {
+        return a1;
+    }
     return nucomp_convert(rb_cComplex, a1, a2, raise);
 }
 
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 652f341fb9..6d5047553b 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -2722,6 +2722,9 @@ f_BigDecimal(int argc, VALUE *argv, VALUE self)
     Real *pv;
     VALUE obj;
 
+    if (argc > 0 && CLASS_OF(argv[0]) == rb_cBigDecimal) {
+        if (argc == 1 || (argc == 2 && RB_TYPE_P(argv[1], T_HASH))) return argv[0];
+    }
     obj = TypedData_Wrap_Struct(rb_cBigDecimal, &BigDecimal_data_type, 0);
     pv = BigDecimal_new(argc, argv);
     if (pv == NULL) return Qnil;
diff --git a/ext/pathname/pathname.c b/ext/pathname/pathname.c
index 70f82583a1..1cf0f90b9f 100644
--- a/ext/pathname/pathname.c
+++ b/ext/pathname/pathname.c
@@ -1323,6 +1323,8 @@ path_unlink(VALUE self)
 static VALUE
 path_f_pathname(VALUE self, VALUE str)
 {
+    if (CLASS_OF(str) == rb_cPathname)
+        return str;
     return rb_class_new_instance(1, &str, rb_cPathname);
 }
 
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index e4f14449a1..b3368b4f4b 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -54,6 +54,11 @@ class TestBigDecimal < Test::Unit::TestCase
     assert_equal(111, BigDecimal("1_1_1_"))
     assert_equal(10**(-1), BigDecimal("1E-1"), '#4825')
     assert_equal(1234, BigDecimal(" \t\n\r \r1234 \t\n\r \r"))
+    bd = BigDecimal.new("1.12", 1)
+    assert_same(bd, BigDecimal(bd))
+    assert_same(bd, BigDecimal(bd, exception: false))
+    assert_not_same(bd, BigDecimal(bd, 1))
+    assert_not_same(bd, BigDecimal(bd, 1, exception: false))
 
     assert_raise(ArgumentError) { BigDecimal("1", -1) }
     assert_raise_with_message(ArgumentError, /"1__1_1"/) { BigDecimal("1__1_1") }
diff --git a/test/pathname/test_pathname.rb b/test/pathname/test_pathname.rb
index eaecc52475..af523f9f98 100644
--- a/test/pathname/test_pathname.rb
+++ b/test/pathname/test_pathname.rb
@@ -471,6 +471,12 @@ class TestPathname < Test::Unit::TestCase
     assert_raise(ArgumentError) { Pathname.new("a\0") }
   end
 
+  def test_global_constructor
+    p = Pathname.new('a')
+    assert_equal(p, Pathname('a'))
+    assert_same(p, Pathname(p))
+  end
+
   class AnotherStringLike # :nodoc:
     def initialize(s) @s = s end
     def to_str() @s end
diff --git a/test/ruby/test_complex.rb b/test/ruby/test_complex.rb
index 2a72f3bcb9..a4fe9d4232 100644
--- a/test/ruby/test_complex.rb
+++ b/test/ruby/test_complex.rb
@@ -123,6 +123,10 @@ class Complex_Test < Test::Unit::TestCase
     assert_raise(TypeError){Complex(Object.new)}
     assert_raise(ArgumentError){Complex()}
     assert_raise(ArgumentError){Complex(1,2,3)}
+    c = Complex(1,0)
+    assert_same(c, Complex(c))
+    assert_same(c, Complex(c, exception: false))
+    assert_raise(ArgumentError){Complex(c, bad_keyword: true)}
 
     if (0.0/0).nan?
       assert_nothing_raised{Complex(0.0/0)}