Bug 24372 – ArraySliceError when calling a function with an optional parameter and typesafe variadic

Tested and reproduced this issue using 2.106.1 and 2.107.0. The following sample will crash the compiler: ``` import std; struct A { } struct B { } struct C { } void test(A a, B b = B.init, scope C[] c...) { writeln(a, b, c); } void main() { testWrap(A()); } ``` The above sample works if `b` or `c` is removed from the signature, or if `c` is defined as `scope C[] c = null...`. While iterating on the arguments, the compiler appears to assume the slice has a corresponding argument passed, but it does not. Related: https://issues.dlang.org/show_bug.cgi?id=14651 Call stack: ``` core.exception.ArraySliceError@src/dmd/mtype.d(4794): slice [2 .. 1] has a larger lower index than upper index ---------------- ??:? onArraySliceError [0x5edb604133da] ??:? _d_arraybounds_slicep [0x5edb60404c32] src/dmd/mtype.d:4794 int dmd.mtype.TypeFunction.callMatch(dmd.mtype.Type, dmd.expression.ArgumentLi st, int, const(char)**, dmd.dscope.Scope*).__foreachbody14(ulong, dmd.mtype.Parameter) [0x5edb60216 f27] src/dmd/mtype.d:6844 int dmd.mtype.Parameter._foreach(dmd.root.array.Array!(dmd.mtype.Parameter).Ar ray*, int delegate(ulong, dmd.mtype.Parameter)).__lambda3!(ulong, dmd.mtype.Parameter, ulong, dmd.m type.Parameter).__lambda3(ulong, dmd.mtype.Parameter, ulong, dmd.mtype.Parameter) [0x5edb6021b030] src/dmd/mtype.d:6889 int dmd.mtype.Parameter._foreachImpl(scope int delegate(ulong, dmd.mtype.Param eter, ulong, dmd.mtype.Parameter), ulong, dmd.mtype.Parameter, ref ulong, dmd.mtype.Parameter) [0x5 edb6021b217] src/dmd/mtype.d:6859 int dmd.mtype.Parameter._foreach(dmd.root.array.Array!(dmd.mtype.Parameter).Ar ray*, int delegate(ulong, dmd.mtype.Parameter, ulong, dmd.mtype.Parameter)) [0x5edb6021b0d8] src/dmd/mtype.d:6844 int dmd.mtype.Parameter._foreach(dmd.root.array.Array!(dmd.mtype.Parameter).Ar ray*, int delegate(ulong, dmd.mtype.Parameter)) [0x5edb6021aff4] src/dmd/mtype.d:6615 int dmd.mtype.ParameterList.opApply(scope int delegate(ulong, dmd.mtype.Parame ter)) [0x5edb6021a8ba] src/dmd/mtype.d:4765 dmd.astenums.MATCH dmd.mtype.TypeFunction.callMatch(dmd.mtype.Type, dmd.expres sion.ArgumentList, int, const(char)**, dmd.dscope.Scope*) [0x5edb60216c10] [...] ```

*** This issue has been marked as a duplicate of issue 14651 ***