[vala/0.40] codegen: Correctly handle cast-expression of real struct to nullable struct

[Rico Tzschichholz <ricotz src gnome org>]

commit d868972188f0bc5b3acb5bc6567fbfb4cda275a1
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 +++++++++++++++++++++
 vala/valadatatype.vala               |  8 ++++++++
 4 files changed, 34 insertions(+)
---
diff --git a/codegen/valaccodebasemodule.vala b/codegen/valaccodebasemodule.vala
index bbdec7c4e..ab142f01d 100644
--- a/codegen/valaccodebasemodule.vala
+++ b/codegen/valaccodebasemodule.vala
@@ -5455,6 +5455,10 @@ 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 ccc76c410..fffb69cbd 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -237,6 +237,7 @@ TESTS = \
        enums/bug780050.vala \
        structs/struct_only.vala \
        structs/struct-base-types.vala \
+       structs/struct-boxed-cast.vala \
        structs/struct-initializer-list-in-array.vala \
        structs/structs.vala \
        structs/constructor-wrong-name.test \
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);
+}
diff --git a/vala/valadatatype.vala b/vala/valadatatype.vala
index ca9d3a61a..ab332f734 100644
--- a/vala/valadatatype.vala
+++ b/vala/valadatatype.vala
@@ -431,6 +431,14 @@ public abstract class Vala.DataType : CodeNode {
                return is_real_struct_type () && !nullable;
        }
 
+       public bool is_non_null_simple_type () {
+               unowned Struct s = data_type as Struct;
+               if (s != null && s.is_simple_type ()) {
+                       return !nullable;
+               }
+               return false;
+       }
+
        /**
         * Returns whether the value needs to be disposed, i.e. whether
         * allocated memory or other resources need to be released when