[DEXTER] Add step.UNKNOWN check to DexTer for None valued steps.

[TWeaver]

Summary

Add unknown step check for null linenos, visual studio debuggers, when debugging an executable produced by clang-cl.exe, are stepping onto lines in main where they cannot recover line number information but is still considered a valid step.

a later step-type check would try to compare a line number with a None value with an int and systematically crash out.

This is a fix for Dexter whereby any steps that are recorded that don't have line number information are classed as step.UNKNOWNS.

[Orlando]

LGTM.

debuginfo-tests/dexter/dex/dextIR/DextIR.py

117

While we're here is column ever None?

[TWeaver]

debuginfo-tests/dexter/dex/dextIR/DextIR.py

117

in this case path, lineno and column are all none. The only valid step information is the function name.

[TWeaver]

debuginfo-tests/dexter/dex/dextIR/DextIR.py

117

'this case' i.e. the motivating case that produced this change. This is the minimum I need to continue working with dexter atm.

[Orlando]

debuginfo-tests/dexter/dex/dextIR/DextIR.py

117

in this case path, lineno and column are all none

Since column can be None then, it may be worth adding similar check? Either way still LGTM.

[TWeaver]

debuginfo-tests/dexter/dex/dextIR/DextIR.py

117

could do... there's two potential definitions. if we stay on the same line but don't know the column movement would you class that as SAME or as UNKNOWN?

debuginfo-tests/dexter/dex/dextIR/DextIR.py

def _get_new_step_kind(self, context, step):
 
         if prev_step.num_frames < step.num_frames:
             return _step_kind_func(context, step)
 
         if prev_step.num_frames > step.num_frames:
             frame_step = self._get_prev_step_in_this_frame(step)
             prev_step = frame_step if frame_step is not None else prev_step
 
+        # If we're missing line numbers to compare then the step kind has to be UNKNOWN.
+        if prev_step.current_location.lineno is None or step.current_location.lineno is None:
+            return StepKind.UNKNOWN
+
         # We're in the same func as prev step, check lineo.
         if prev_step.current_location.lineno > step.current_location.lineno:
             return StepKind.VERTICAL_BACKWARD
 
         if prev_step.current_location.lineno < step.current_location.lineno:
             return StepKind.VERTICAL_FORWARD
 
         # We're on the same line as prev step, check column.
         if prev_step.current_location.column > step.current_location.column:
             return StepKind.HORIZONTAL_BACKWARD
 
         if prev_step.current_location.column < step.current_location.column:
             return StepKind.HORIZONTAL_FORWARD
 
         # This step is in exactly the same location as the prev step.
         return StepKind.SAME
 
     def new_step(self, context, step):
         assert isinstance(step, StepIR), type(step)
         step.step_kind = self._get_new_step_kind(context, step)
         self.steps.append(step)
         return step
 
     def clear_steps(self):
         self.steps.clear()