From 988e77e02104f71fda5190de7e509f0ceca2283a Mon Sep 17 00:00:00 2001
From: Rico Tzschichholz <ricotz@ubuntu.com>
Date: Sun, 3 Nov 2019 20:03:20 +0100
Subject: vala: Improve error reporting for invalid interface prerequisites

Fixes https://gitlab.gnome.org/GNOME/vala/issues/437
---
 tests/Makefile.am                                       |  2 ++
 tests/semantic/interface-prerequisite-invalid.test      | 11 +++++++++++
 .../interface-prerequisite-less-accessible.test         | 10 ++++++++++
 vala/valainterface.vala                                 | 17 +++++------------
 4 files changed, 28 insertions(+), 12 deletions(-)
 create mode 100644 tests/semantic/interface-prerequisite-invalid.test
 create mode 100644 tests/semantic/interface-prerequisite-less-accessible.test

diff --git a/tests/Makefile.am b/tests/Makefile.am
index 292eea0c7..5794aa162 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -709,6 +709,8 @@ TESTS = \
 	semantic/foreach-next-void.test \
 	semantic/foreach-wrong-types.test \
 	semantic/initializer-unknown-type.test \
+	semantic/interface-prerequisite-invalid.test \
+	semantic/interface-prerequisite-less-accessible.test \
 	semantic/localvariable-owned-to-unowned.test \
 	semantic/localvariable-var-static-access-instance-field.test \
 	semantic/localvariable-var-static-access-instance-method.test \
diff --git a/tests/semantic/interface-prerequisite-invalid.test b/tests/semantic/interface-prerequisite-invalid.test
new file mode 100644
index 000000000..304e27902
--- /dev/null
+++ b/tests/semantic/interface-prerequisite-invalid.test
@@ -0,0 +1,11 @@
+Invalid Code
+
+struct Bar {
+	public int i;
+}
+
+interface Foo : Bar {
+}
+
+void main () {
+}
diff --git a/tests/semantic/interface-prerequisite-less-accessible.test b/tests/semantic/interface-prerequisite-less-accessible.test
new file mode 100644
index 000000000..3855ea47f
--- /dev/null
+++ b/tests/semantic/interface-prerequisite-less-accessible.test
@@ -0,0 +1,10 @@
+Invalid Code
+
+class Bar {
+}
+
+public interface Foo : Bar {
+}
+
+void main () {
+}
diff --git a/vala/valainterface.vala b/vala/valainterface.vala
index 44613f9ef..eb63e9a05 100644
--- a/vala/valainterface.vala
+++ b/vala/valainterface.vala
@@ -176,28 +176,21 @@ public class Vala.Interface : ObjectTypeSymbol {
 		/* check prerequisites */
 		Class prereq_class = null;
 		foreach (DataType prereq in get_prerequisites ()) {
-			TypeSymbol class_or_interface = prereq.type_symbol;
-			/* skip on previous errors */
-			if (class_or_interface == null) {
+			if (!(prereq is ObjectType)) {
 				error = true;
-				continue;
-			}
-
-			if (!(class_or_interface is ObjectTypeSymbol)) {
-				error = true;
-				Report.error (source_reference, "Prerequisite `%s' of interface `%s' is not a class or interface".printf (get_full_name (), class_or_interface.to_string ()));
+				Report.error (source_reference, "Prerequisite `%s' of interface `%s' is not a class or interface".printf (prereq.to_string (), get_full_name ()));
 				return false;
 			}
 
 			/* interfaces are not allowed to have multiple instantiable prerequisites */
-			if (class_or_interface is Class) {
+			if (prereq.type_symbol is Class) {
 				if (prereq_class != null) {
 					error = true;
-					Report.error (source_reference, "%s: Interfaces cannot have multiple instantiable prerequisites (`%s' and `%s')".printf (get_full_name (), class_or_interface.get_full_name (), prereq_class.get_full_name ()));
+					Report.error (source_reference, "%s: Interfaces cannot have multiple instantiable prerequisites (`%s' and `%s')".printf (get_full_name (), prereq.type_symbol.get_full_name (), prereq_class.get_full_name ()));
 					return false;
 				}
 
-				prereq_class = (Class) class_or_interface;
+				prereq_class = (Class) prereq.type_symbol;
 			}
 		}
 
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