Also write to a log file by default

Write the log of outcome analysis to a log file by default. This is a cheap
way of getting the outcome analysis log in an easy-to-access form on the CI:
with our current CI scripts, they are now automatically available as an
artifact called `analyze_outcomes.log`.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

scripts/mbedtls_framework/outcome_analysis.py

@@ -47,9 +47,20 @@
 class Results:
     """Process analysis results."""
 
-    def __init__(self):
+    def __init__(self,
+                 stderr: bool = True,
+                 log_file: str = '') -> None:
+        """Log and count errors.
+
+        Log to stderr if stderr is true.
+        Log to log_file if specified and non-empty.
+        """
         self.error_count = 0
         self.warning_count = 0
+        self.stderr = stderr
+        self.log_file = None
+        if log_file:
+            self.log_file = open(log_file, 'w', encoding='utf-8')
 
     def new_section(self, fmt, *args, **kwargs):
         self._print_line('\n*** ' + fmt + ' ***\n', *args, **kwargs)
@@ -65,9 +76,12 @@ def warning(self, fmt, *args, **kwargs):
         self.warning_count += 1
         self._print_line('Warning: ' + fmt, *args, **kwargs)
 
-    @staticmethod
-    def _print_line(fmt, *args, **kwargs):
-        sys.stderr.write((fmt + '\n').format(*args, **kwargs))
+    def _print_line(self, fmt, *args, **kwargs):
+        line = (fmt + '\n').format(*args, **kwargs)
+        if self.stderr:
+            sys.stderr.write(line)
+        if self.log_file:
+            self.log_file.write(line)
 
 def execute_reference_driver_tests(results: Results, ref_component: str, driver_component: str, \
                                    outcome_file: str) -> None:
@@ -284,8 +298,6 @@ def run(self, results: Results, outcomes: Outcomes) -> None:
 
 
 def main(known_tasks: typing.Dict[str, typing.Type[Task]]) -> None:
-    main_results = Results()
-
     try:
         parser = argparse.ArgumentParser(description=__doc__)
         parser.add_argument('outcomes', metavar='OUTCOMES.CSV',
@@ -297,6 +309,10 @@ def main(known_tasks: typing.Dict[str, typing.Type[Task]]) -> None:
                                  'comma/space-separated list of tasks. ')
         parser.add_argument('--list', action='store_true',
                             help='List all available tasks and exit.')
+        parser.add_argument('--log-file',
+                            default='tests/analyze_outcomes.log',
+                            help='Log file (default: tests/analyze_outcomes.log;'
+                                 ' empty means no log file)')
         parser.add_argument('--require-full-coverage', action='store_true',
                             dest='full_coverage', help="Require all available "
                             "test cases to be executed and issue an error "
@@ -309,6 +325,8 @@ def main(known_tasks: typing.Dict[str, typing.Type[Task]]) -> None:
                 print(task_name)
             sys.exit(0)
 
+        main_results = Results(log_file=options.log_file)
+
         if options.specified_tasks == 'all':
             tasks_list = list(known_tasks.keys())
         else: