[vala/staging] vala: Don't allow casting to void

[Rico Tzschichholz <ricotz src gnome org>]

commit 051b8a13abb371ed21513ac16acd0f7dfa069dfd
Author: Colin Kiama <colinkiama gmail com>
Date:   Sun Sep 12 19:11:00 2021 +0100

    vala: Don't allow casting to void
    
    Fixes https://gitlab.gnome.org/GNOME/vala/issues/1070

 tests/Makefile.am                         | 1 +
 tests/semantic/cast-void-not-allowed.test | 9 +++++++++
 vala/valacastexpression.vala              | 6 ++++++
 3 files changed, 16 insertions(+)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index ec9c97b13..5d3a6ee9b 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -948,6 +948,7 @@ TESTS = \
        semantic/assignment-signal-incompatible-type.test \
        semantic/cast-gvalue-unsupported.test \
        semantic/cast-gvariant-unsupported.test \
+       semantic/cast-void-not-allowed.test \
        semantic/chainup-gobject-incompatible-type-property.test \
        semantic/chainup-gobject-unknown-property.test \
        semantic/chainup-gobject-unsupported-type-property.test \
diff --git a/tests/semantic/cast-void-not-allowed.test b/tests/semantic/cast-void-not-allowed.test
new file mode 100644
index 000000000..965ef235c
--- /dev/null
+++ b/tests/semantic/cast-void-not-allowed.test
@@ -0,0 +1,9 @@
+Invalid Code
+
+bool foo () {
+       return true;
+}
+
+void main () {
+       (void) foo ();
+}
diff --git a/vala/valacastexpression.vala b/vala/valacastexpression.vala
index 9aff511fa..732b99a71 100644
--- a/vala/valacastexpression.vala
+++ b/vala/valacastexpression.vala
@@ -164,6 +164,12 @@ public class Vala.CastExpression : Expression {
 
                // FIXME: check whether cast is allowed
 
+               if (type_reference is VoidType) {
+                       Report.error (source_reference, "Casting to `void' is not allowed");
+                       error = true;
+                       return false;
+               }
+
                if (type_reference is DelegateType && inner.value_type is MethodType) {
                        if (target_type != null) {
                                inner.value_type.value_owned = target_type.value_owned;