[LIT] Add JSONMetricValue type to wrap types supported by the json encoder.

[EricWF]

Summary

The following types can be encoded and decoded by the json library:
dict, list, tuple, str, unicode, int, long, float, bool, NoneType.

JSONMetricValue can be constructed with any of these types, and used as part of Test.Result.
This patch also adds a toMetricValue function that converts a value into a MetricValue.

[• ddunbar]

The MetricValue abstraction doesn't currently provide any value really, but it is there in case we ever wanted to make use of the values (e.g., report performance changes). Given that, I think it probably makes sense to just call this JSONMetricValue and make it explicit that this is tied to values which are representable in the output, but which will otherwise be uninterpreted.

utils/lit/lit/Test.py

78

Wouldn't isinstance() be more canonical?

Also, this should probably verify that the container data types themselves contain representable items. Does the json lib provide a function to do that?

96

Same note re: isinstance().

[EricWF]

I'll make the requested changes.

utils/lit/lit/Test.py

78

You could create a JSONEncoder object and encode it on the spot and throw away the result. However there is nothing you can do to prevent the value from changing after the check.

You can't keep the encoded string because you'll end up re-encoding the string later.

[EricWF]

Implement @ddunbar's changes.

[• ddunbar]

LGTM

[EricWF]

Remove poorly named function. It's unneeded.

[EricWF]

Accepting.

utils/lit/lit/Test.py

 import os
 from xml.sax.saxutils import escape
+from json import JSONEncoder
 
 # Test result codes.
 

     def todata(self):
         return self.value
 
+
+def isJSONMetricValue(value):
+    try:
+        e = JSONEncoder()
+        e.encode(value)
+        return True
+    except TypeError:
+        return False
+
+class JSONMetricValue(MetricValue):
+    """
+        JSONMetricValue is used for types that are representable in the output
+        but that are otherwise uninterpreted.
+    """
+    def __init__(self, value):
+        # Ensure the value is a serializable by trying to encode it.
+        # WARNING: The value may change before it is encoded again, and may
+        #          not be encodable after the change.
+        try:
+            e = JSONEncoder()
+            e.encode(value)
+        except TypeError:
+            raise
+        self.value = value
+
+    def format(self):
+        return str(self.value)
+
+    def todata(self):
+        return self.value
+
+def toMetricValue(value):
+    if isinstance(value, MetricValue):
+        return value
+    elif isinstance(value, int) or isinstance(value, long):
+        return IntMetricValue(value)
+    elif isinstance(value, float):
+        return RealMetricValue(value)
+    else:
+        # Try to create a JSONMetricValue and let the constructor throw
+        # if value is not a valid type.
+        return JSONMetricValue(value)
+
+
 # Test results.
 
 class Result(object):