[crashlog] Change heuristic to stripping the meta data from crashlogs

[JDevlieghere]

Summary

Instead of pro-actively trying to determine if the first line in a crashlog contains meta data, change the heuristic to trying to parse the whole file first. If that fails, strip the first line and try again. If that fails again, we assume the input is not JSON and we fall back to the old textual parser.

rdar://88580543

[mib]

LGTM

lldb/examples/python/crashlog.py

def get_target(self):
         return self.target
 
 
 class CrashLogFormatException(Exception):
     pass
 
 
 class CrashLogParseException(Exception):
     pass
 
 
 class CrashLogParser:
     def parse(self, debugger, path, verbose):
         try:
             return JSONCrashLogParser(debugger, path, verbose).parse()
         except CrashLogFormatException:
             return TextCrashLogParser(debugger, path, verbose).parse()
 
 
 class JSONCrashLogParser:
     def __init__(self, debugger, path, verbose):
         self.path = os.path.expanduser(path)
         self.verbose = verbose
         self.crashlog = CrashLog(debugger, self.path, self.verbose)
 
+    def parse_json(self, buffer):
+        try:
+            return json.loads(buffer)
+        except:
+            # The first line can contain meta data. Try stripping it and try
+            # again.
+            head, _, tail = buffer.partition('\n')
+            return json.loads(tail)
+
     def parse(self):
         with open(self.path, 'r') as f:
             buffer = f.read()
 
-        # Skip the first line if it contains meta data.
-        head, _, tail = buffer.partition('\n')
         try:
-            metadata = json.loads(head)
-            if 'app_name' in metadata and 'app_version' in metadata:
-                buffer = tail
-        except ValueError:
-            pass
-
-        try:
-            self.data = json.loads(buffer)
-        except ValueError:
+            self.data = self.parse_json(buffer)
+        except:
             raise CrashLogFormatException()
 
         try:
             self.parse_process_info(self.data)
             self.parse_images(self.data['usedImages'])
             self.parse_threads(self.data['threads'])
             self.parse_errors(self.data)
             thread = self.crashlog.threads[self.crashlog.crashed_thread_idx]