[vala/0.48] vala: Handle parameter initializer without value-type

[Rico Tzschichholz <ricotz src gnome org>]

commit 96830fa9ae978c88f9b0fb226cb56104e0d11378
Author: Rico Tzschichholz <ricotz ubuntu com>
Date:   Sat Jul 11 19:06:04 2020 +0200

    vala: Handle parameter initializer without value-type
    
    This caused criticals like:
    
      vala_data_type_compatible: assertion 'self != NULL' failed
    
    See https://gitlab.gnome.org/GNOME/vala/issues/1029

 tests/Makefile.am                                 | 1 +
 tests/generics/parameter-invalid-initializer.test | 8 ++++++++
 vala/valaparameter.vala                           | 3 +++
 3 files changed, 12 insertions(+)
---
diff --git a/tests/Makefile.am b/tests/Makefile.am
index 99e4d5f6f..a2ac4958d 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -588,6 +588,7 @@ TESTS = \
        generics/inference-argument-may-fail.vala \
        generics/inference-static-function.vala \
        generics/integer-type-cast.vala \
+       generics/parameter-invalid-initializer.test \
        generics/parameter-sizeof-initializer.vala \
        generics/member-dup-destroy.vala \
        generics/string-literal-comparison.vala \
diff --git a/tests/generics/parameter-invalid-initializer.test 
b/tests/generics/parameter-invalid-initializer.test
new file mode 100644
index 000000000..d3b8b80d4
--- /dev/null
+++ b/tests/generics/parameter-invalid-initializer.test
@@ -0,0 +1,8 @@
+Invalid Code
+
+class Class<G> {
+    public Class (Type type = G);
+}
+
+void main () {
+}
diff --git a/vala/valaparameter.vala b/vala/valaparameter.vala
index 0267a7675..339fd615c 100644
--- a/vala/valaparameter.vala
+++ b/vala/valaparameter.vala
@@ -166,6 +166,9 @@ public class Vala.Parameter : Variable {
                        if (initializer != null) {
                                initializer.target_type = variable_type.copy ();
                                initializer.check (context);
+                               if (initializer.value_type == null) {
+                                       initializer.value_type = new InvalidType ();
+                               }
                        }
 
                        unowned ArrayType? variable_array_type = variable_type as ArrayType;