[Mono-bugs] [Bug 614471] New: [GMCS] Regression: Can assign invalid types to variables.

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http://bugzilla.novell.com/show_bug.cgi?id=614471

http://bugzilla.novell.com/show_bug.cgi?id=614471#c0


           Summary: [GMCS] Regression: Can assign invalid types to
                    variables.
    Classification: Mono
           Product: Mono: Compilers
           Version: SVN
          Platform: x86-64
        OS/Version: openSUSE 11.2
            Status: NEW
          Severity: Normal
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: jpryor at novell.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---
           Blocker: ---


The type checker in trunk has gone haywire; to wit, this compiles:


    class Test {
        public static void Main ()
        {
            Foo<int, double>();
        }

        static void Foo<T1, T2> ()
        {
            T1 a = default (T2);
            T2 b = default (T1);
        }
    }

There's no way that we should be able to assign default(T2) to a T1 variable.

gmcs 2.4 dislikes it, as does gmcs 2.6:
  bad.cs(9,28): error CS0029: Cannot implicitly convert type `T2' to `T1'
  bad.cs(10,28): error CS0029: Cannot implicitly convert type `T1' to `T2'

(gmcs 2.6 shows lots more output, but it's a superset of the above.)

gmcs trunk will compile it with only warnings:

bad.cs(10,28): warning CS0219: The variable `b' is assigned but its value is
never used
bad.cs(9,28): warning CS0219: The variable `a' is assigned but its value is
never used

Running it is a disaster:

$ mono bad.exe 

Unhandled Exception: System.InvalidCastException: Cannot cast from source type
to destination type.
  at Test.Foo[Int32,Double] () [0x00000] in <filename unknown>:0 
  at Test.Main () [0x00000] in <filename unknown>:0

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