tests/basics: Add more tests for return within try-finally.

tests/basics/try_finally_return4.py

@@ -0,0 +1,83 @@
+# test try-finally with return, where unwinding return has to go through
+# another try-finally which may affect the behaviour of the return
+
+# case where a simple try-finally executes during an unwinding return
+def f(x):
+    try:
+        try:
+            if x:
+                return 42
+        finally:
+            try:
+                print(1)
+            finally:
+                print(2)
+            print(3)
+        print(4)
+    finally:
+        print(5)
+print(f(0))
+print(f(1))
+
+# case where an unwinding return is replaced by another one
+def f(x):
+    try:
+        try:
+            if x:
+                return 42
+        finally:
+            try:
+                print(1)
+                return 43
+            finally:
+                print(2)
+            print(3)
+        print(4)
+    finally:
+        print(5)
+print(f(0))
+print(f(1))
+
+# case where an unwinding return is cancelled by an exception
+def f(x):
+    try:
+        try:
+            if x:
+                return 42
+        finally:
+            try:
+                print(1)
+                raise ValueError # cancels any active return
+            finally:
+                print(2)
+            print(3)
+        print(4)
+    finally:
+        print(5)
+try:
+    print(f(0))
+except:
+    print('caught')
+try:
+    print(f(1))
+except:
+    print('caught')
+
+# case where an unwinding return is cancelled then resumed
+def f(x):
+    try:
+        try:
+            if x:
+                return 42
+        finally:
+            try:
+                print(1)
+                raise Exception # cancels any active return
+            except: # cancels the exception and resumes any active return
+                print(2)
+            print(3)
+        print(4)
+    finally:
+        print(5)
+print(f(0))
+print(f(1))