Add some failure tests for inheritance

test/error/cycle/ClassCycle.pth

@@ -0,0 +1,29 @@
+// Plinth Test
+// Compiler: ClassCycle.pth: 9:1-26: Cyclic inheritance hierarchy detected: Alpha extends itself (perhaps indirectly).
+// Compiler: ClassCycle.pth: 13:1-28: Cyclic inheritance hierarchy detected: Bravo extends itself (perhaps indirectly).
+// Compiler: ClassCycle.pth: 16:1-28: Cyclic inheritance hierarchy detected: Charlie extends itself (perhaps indirectly).
+// Compiler: ClassCycle.pth: 20:1-28: Cyclic inheritance hierarchy detected: Delta extends itself (perhaps indirectly).
+// Compiler: ClassCycle.pth: 23:1-25: Cyclic inheritance hierarchy detected: Echo extends itself (perhaps indirectly).
+// Compiler: ClassCycle.pth: 26:1-27: Cyclic inheritance hierarchy detected: Foxtrot extends itself (perhaps indirectly).
+
+class Alpha extends Alpha
+{
+}
+
+class Bravo extends Charlie
+{
+}
+class Charlie extends Bravo
+{
+}
+
+class Delta extends Foxtrot
+{
+}
+class Echo extends Delta
+{
+}
+class Foxtrot extends Echo
+{
+}
+

test/error/cycle/InterfaceCycle.pth

@@ -0,0 +1,31 @@
+// Plinth Test
+// Compiler: InterfaceCycle.pth: 8:1-30: Cyclic inheritance graph detected: Alpha extends itself (perhaps indirectly)
+// Compiler: InterfaceCycle.pth: 12:1-39: Cyclic inheritance graph detected: Bravo extends itself (perhaps indirectly)
+// Compiler: InterfaceCycle.pth: 15:1-32: Cyclic inheritance graph detected: Charlie extends itself (perhaps indirectly)
+// Compiler: InterfaceCycle.pth: 25:1-37: Cyclic inheritance graph detected: Foxtrot extends itself (perhaps indirectly)
+// Compiler: InterfaceCycle.pth: 28:1-37: Cyclic inheritance graph detected: Golf extends itself (perhaps indirectly)
+
+interface Alpha extends Alpha
+{
+}
+
+interface Bravo extends Charlie, Alpha
+{
+}
+interface Charlie extends Bravo
+{
+}
+
+interface Delta
+{
+}
+interface Echo extends Delta
+{
+}
+interface Foxtrot extends Golf, Echo
+{
+}
+interface Golf extends Echo, Foxtrot
+{
+}
+

test/error/inheritance/ClassInheritance.pth

@@ -0,0 +1,28 @@
+// Plinth Test
+// Compiler: ClassInheritance.pth: 7:1-27: A class may not extend a compound type
+// Compiler: ClassInheritance.pth: 14:1-28: A class may not extend an interface
+// Compiler: ClassInheritance.pth: 21:1-28: A class may not implement another class
+// Compiler: ClassInheritance.pth: 25:1-32: A class may not implement a compound type
+
+class Alpha extends string
+{
+}
+
+interface Bravo
+{
+}
+class Charlie extends Bravo
+{
+}
+
+class Delta
+{
+}
+class Echo implements Delta
+{
+}
+
+class Foxtrot implements string
+{
+}
+

test/error/inheritance/InterfaceInheritance.pth

@@ -0,0 +1,15 @@
+// Plinth Test
+// Compiler: InterfaceInheritance.pth: 8:1-30: An interface may not extend a class
+// Compiler: InterfaceInheritance.pth: 12:1-33: An interface may not extend a compound type
+
+class Alpha
+{
+}
+interface Bravo extends Alpha
+{
+}
+
+interface Charlie extends string
+{
+}
+

test/error/inheritance/Linearisation.pth

@@ -0,0 +1,17 @@
+// Plinth Test
+// Compiler: Linearisation.pth: 14:1-38: Cannot find a good linearisation for the inheritance hierarchy of Charlie: cannot decide which of the following super-types should be preferred:
+// Compiler: Alpha
+// Compiler: Bravo
+
+interface Alpha
+{
+}
+
+interface Bravo extends Alpha
+{
+}
+
+class Charlie implements Alpha, Bravo
+{
+}
+