[Gardening] Update the utils/backtrace-check script to use more modern Python formatting.

utils/backtrace-check

@@ -1,54 +1,82 @@
 #!/usr/bin/env python
 
-# This script uses a regex to validate the output of our backtraces.
-# The layout we assume is:
-#
-# <frame number> <library name> <address> <demangled name> + <offset>
-#
-# It currently just checks that the backtrace results in at least one correctly
-# formatted entry. It does not directly validate the input since the output
-# would not be robust against standard library changes.
-#
-# TODO: We could have the user pass in the frame number, library name, and
-# demangled name. These we can always validate as true in a robust way. On the
-# other hand, address and offset are more difficult to validate in a robust way
-# in the face of small codegen differences, so without any further thought I
-# imagine we can just check the format.
-#
-# 11 libswiftCore.dylib 0x000000000dce84d0l _fatalErrorMessage(StaticString,
-# StaticString, StaticString, UInt, flags : UInt32) -> () + 444
-
-from __future__ import print_function
+
+"""
+This script uses a regex to validate the output of our backtraces.
+The layout we assume is:
+
+<frame number> <library name> <address> <demangled name> + <offset>
+
+It currently just checks that the backtrace results in at least one correctly
+formatted entry. It does not directly validate the input since the output
+would not be robust against standard library changes.
+
+TODO: We could have the user pass in the frame number, library name, and
+demangled name. These we can always validate as true in a robust way. On the
+other hand, address and offset are more difficult to validate in a robust way
+in the face of small codegen differences, so without any further thought I
+imagine we can just check the format.
+
+11 libswiftCore.dylib 0x000000000dce84d0l _fatalErrorMessage(StaticString,
+StaticString, StaticString, UInt, flags : UInt32) -> () + 444
+"""
+
+
+from __future__ import absolute_import, print_function, unicode_literals
 
 import argparse
 import re
 import sys
 
 
-def main():
+# -----------------------------------------------------------------------------
+# Constants
+
+DESCRIPTION = """
+Checks that a stacktrace dump follows canonical formatting.
+"""
+
+TARGET_PATTERN = re.compile(
+    r'(?P<index>\d+) +(?P<object>\S+) +(?P<address>0x[0-9a-fA-F]{16}) '
+    r'(?P<routine>[^+]+) [+] (?P<offset>\d+)')
+
+RESULTS_FORMAT = """Stack Trace Entry:
+\tIndex: '%(index)s'
+\tObject File: '%(object)s'
+\tAddress: '%(address)s'
+\tRoutine: '%(routine)s'
+\tOffset: '%(offset)s'
+"""
+
+
+# -----------------------------------------------------------------------------
+
+def parse_args():
     parser = argparse.ArgumentParser(
         formatter_class=argparse.RawDescriptionHelpFormatter,
-        description="""Checks that a stacktrace dump follows canonical
-formatting.""")
+        description=DESCRIPTION)
+
     parser.add_argument(
-        "-u", "--check-unavailable", action='store_true',
-        help="Checks if any symbols were unavailable")
-    args = parser.parse_args()
+        '-u', '--check-unavailable',
+        action='store_true',
+        help='Checks if any symbols were unavailable')
 
-    TARGET_RE = re.compile(
-        r"(?P<index>\d+) +(?P<object>\S+) +(?P<address>0x[0-9a-fA-F]{16}) "
-        r"(?P<routine>[^+]+) [+] (?P<offset>\d+)")
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
 
     lines = sys.stdin.readlines()
 
     found_stack_trace_start = False
     found_stack_trace_entry = False
     for line in lines:
-        line = line.rstrip("\n")
+        line = line.rstrip('\n')
 
         # First see if we found the start of our stack trace start. If so, set
         # the found stack trace flag and continue.
-        if line == "Current stack trace:":
+        if line == 'Current stack trace:':
             assert(not found_stack_trace_start)
             found_stack_trace_start = True
             continue
@@ -59,21 +87,19 @@ formatting.""")
             continue
 
         # Ok, we are in the middle of matching a stack trace entry.
-        m = TARGET_RE.match(line)
+        matches = TARGET_PATTERN.match(line)
+
         # If we fail to match, we have exited the stack trace entry region
-        if m is None:
+        if matches is None:
             break
 
         # At this point, we know that we have some sort of match.
         found_stack_trace_entry = True
-        print("Stack Trace Entry:")
-        print("\tIndex: '%(index)s'\n\tObject File: '%(object)s'\n\tAddress: "
-              "'%(address)s'\n\tRoutine: '%(routine)s'\n\tOffset: '%(offset)s'"
-              "\n" % m.groupdict())
+        print(RESULTS_FORMAT.format(**matches.groupdict()))
 
         # Check for unavailable symbols, if that was requested.
         if args.check_unavailable:
-            assert("unavailable" not in m.group("routine"))
+            assert('unavailable' not in matches.group('routine'))
 
     # Once we have processed all of the lines, make sure that we found at least
     # one stack trace entry.