allow implicit cast from &const to ?&const &const

Allow implicit casts from n-th degree const pointers to nullable const
pointers of degree n+1.  That is:

    fn f() void {
        const s = S {};
        const p = &s;
        g(p);   // Works.
        g(&p);  // So does this.
    }

    fn g(_: ?&const &const S) void {  // Nullable 2nd degree const ptr.
    }

Fixes #731 some more.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/ir.cpp b/src/ir.cpp
index e79235830c..b1fd7104ea 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -8830,7 +8830,8 @@ static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_inst
             }
         } else if (wanted_child_type->id == TypeTableEntryIdPointer &&
                    wanted_child_type->data.pointer.is_const &&
-                   is_container(actual_type)) {
+                   (actual_type->id == TypeTableEntryIdPointer || is_container(actual_type)))
+        {
             IrInstruction *cast1 = ir_analyze_cast(ira, source_instr, wanted_child_type, value);
             if (type_is_invalid(cast1->value.type))
                 return ira->codegen->invalid_instruction;