[Bug #19004] `Complex.polar` handles complex singular `abs` argument

`Complex.polar` accepts Complex values as arguments for the polar form as long
as the value of the complex has no imaginary part (ie it is 'real'). In
`f_complex_polar` this is handled by extracting the real part of the arguments.
However in the case `polar` is called with only a single argument, the absolute
value (abs), then the Complex is created without applying a check on the type
of abs, meaning it is possible to create a Complex where the real part is itself
an instance of a Complex. This change removes the short circuit for the single
argument case meaning the real part extraction is performed correctly
(by f_complex_polar).

Also adds an example to `spec/ruby/core/complex/polar_spec.rb` to check that
the real part of a complex argument is correctly extracted and used in the
resulting Complex real and imaginary parts.

1 files changed, 6 insertions, 7 deletions

diff --git a/complex.c b/complex.c
index 18d61b206f..c4f0f5e8c9 100644
--- a/complex.c
+++ b/complex.c
@@ -704,14 +704,13 @@ nucomp_s_polar(int argc, VALUE *argv, VALUE klass)
 {
     VALUE abs, arg;
 
-    switch (rb_scan_args(argc, argv, "11", &abs, &arg)) {
-      case 1:
-        nucomp_real_check(abs);
-        return nucomp_s_new_internal(klass, abs, ZERO);
-      default:
-        nucomp_real_check(abs);
+    argc = rb_scan_args(argc, argv, "11", &abs, &arg);
+    nucomp_real_check(abs);
+    if (argc == 2) {
         nucomp_real_check(arg);
-        break;
+    }
+    else {
+        arg = ZERO;
     }
     return f_complex_polar(klass, abs, arg);
 }