[vala/wip/issue/991] codegen: Correctly handle cast-expression of real struct to nullable struct

[Rico Tzschichholz <ricotz src gnome org>]

commit 80f45a629ee9756c8ccc96952f6683e75d169ec0
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sun May 10 08:46:33 2020 +0200

    codegen: Correctly handle cast-expression of real struct to nullable struct
    
    Don't generate invalid c-code leading to "cannot convert to a pointer type"
    
    Fix https://gitlab.gnome.org/GNOME/vala/issues/991

 codegen/valaccodebasemodule.vala     |  4 ++++
 tests/Makefile.am                    |  1 +
 tests/structs/struct-boxed-cast.vala | 21 +++++++++++++++++++++
 3 files changed, 26 insertions(+)
---
diff --git a/codegen/valaccodebasemodule.vala b/codegen/valaccodebasemodule.vala
index fb3c70154..b4a65dd77 100644
--- a/codegen/valaccodebasemodule.vala
+++ b/codegen/valaccodebasemodule.vala
@@ -5342,6 +5342,10 @@ public abstract class Vala.CCodeBaseModule : CodeGenerator {
                        expr.inner.value_type is ValueType && expr.inner.value_type.nullable) {
                        // nullable integer or float or boolean or struct or enum cast to non-nullable
                        innercexpr = new CCodeUnaryExpression (CCodeUnaryOperator.POINTER_INDIRECTION, 
innercexpr);
+               } else if (expr.type_reference is ValueType && expr.type_reference.nullable &&
+                       expr.inner.value_type.is_real_non_null_struct_type ()) {
+                       // real non-null struct cast to nullable
+                       innercexpr = new CCodeUnaryExpression (CCodeUnaryOperator.ADDRESS_OF, innercexpr);
                } else if (expr.type_reference is ArrayType && !(expr.inner is Literal)
                    && expr.inner.value_type is ValueType && !expr.inner.value_type.nullable) {
                        // integer or float or boolean or struct or enum to array cast
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 2bbd07efe..160d77169 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -268,6 +268,7 @@ TESTS = \
        enums/bug780050.vala \
        structs/struct_only.vala \
        structs/struct-base-types.vala \
+       structs/struct-boxed-cast.vala \
        structs/struct-empty-still.test \
        structs/struct-initializer-list-in-array.vala \
        structs/struct-no-gtype.vala \
diff --git a/tests/structs/struct-boxed-cast.vala b/tests/structs/struct-boxed-cast.vala
new file mode 100644
index 000000000..260819dcf
--- /dev/null
+++ b/tests/structs/struct-boxed-cast.vala
@@ -0,0 +1,21 @@
+void foo<T> (T t) {
+       assert (((Bar?) t).s == "foo");
+       assert (((Bar?) t).i == 23);
+}
+
+struct Bar {
+       public string s;
+       public int i;
+}
+
+void main () {
+       Bar f = { "bar", 42 };
+       var cast = (Bar?) f;
+       assert (cast.s == "bar");
+       assert (cast.i == 42);
+
+       Bar arg = { "foo", 23 };
+       foo ((Bar?) arg);
+       foo<Bar?> (arg);
+       foo<Bar?> ((Bar?) arg);
+}