Add broken FS switch behaviour for compatibility.

In the absence of a 'default' label within a switch, FS falls through to the first CASE label (or to the code before the first CASE if there's any).

This commit adds an option, active by default for FS compatibility, that mimics this broken behaviour, as well as a warning in case the 'default' label is absent, which also triggers another warning when the option is active.

lslopt/lslparse.py

@@ -1674,10 +1674,15 @@ list lazy_list_set(list L, integer i, list v)
                     ]})
 
             if switchcasedefault is None:
-                switchcasedefault = brk
-                self.breakstack[-1][2] = True
-            prelude.append({'nt':'JUMP', 't':None, 'name':switchcasedefault,
-                'scope':blkscope})
+                warning("No 'default:' label in switch statement")
+                if self.brokennodefault:
+                    warning("Broken behaviour active - falling through")
+                if not self.brokennodefault:
+                    switchcasedefault = brk
+                    self.breakstack[-1][2] = True
+            if switchcasedefault is not None:
+                prelude.append({'nt':'JUMP', 't':None, 'name':switchcasedefault,
+                    'scope':blkscope})
             last = self.breakstack.pop()
             if last[2]:
                 blk.append({'nt':'@', 'name':brk, 'scope':blkscope})
@@ -2311,6 +2316,9 @@ list lazy_list_set(list L, integer i, list v)
         if self.enableswitch:
             self.keywords |= frozenset(('switch', 'case', 'break'))
 
+        # Broken behaviour in the absence of a default: label in a switch stmt.
+        self.brokennodefault = 'brokennodefault' in options
+
         # Allow brackets for assignment of list elements e.g. mylist[5]=4
         self.lazylists = 'lazylists' in options