ci: Include context from failed build logs in the CI job log

This is faster to look up than browsing or downloading artifacts, and will often
contain the root cause.

Context includes the last 25 lines of the log, and any lines contaiing 'error:'
or 'warning:'

tools/build_apps.py

@@ -7,11 +7,19 @@
 
 import argparse
 import logging
+import os.path
+import re
 import sys
 
 from find_build_apps import BUILD_SYSTEMS, BuildError, BuildItem, setup_logging
 from find_build_apps.common import SIZE_JSON_FN, rmdir
 
+# This RE will match GCC errors and many other fatal build errors and warnings as well
+LOG_ERROR_WARNING = re.compile(r'(error|warning):', re.IGNORECASE)
+
+# Log this many trailing lines from a failed build log, also
+LOG_DEBUG_LINES = 25
+
 
 def main():  # type: () -> None
     parser = argparse.ArgumentParser(description='ESP-IDF app builder')
@@ -120,6 +128,17 @@ def main():  # type: () -> None
             build_system_class.build(build_info)
         except BuildError as e:
             logging.error(str(e))
+            if build_info.build_log_path:
+                log_filename = os.path.basename(build_info.build_log_path)
+                with open(build_info.build_log_path, 'r') as f:
+                    lines = [line.rstrip() for line in f.readlines() if line.rstrip()]  # non-empty lines
+                    logging.debug('Error and warning lines from {}:'.format(log_filename))
+                    for line in lines:
+                        if LOG_ERROR_WARNING.search(line):
+                            logging.warning('>>> {}'.format(line))
+                    logging.debug('Last {} lines of {}:'.format(LOG_DEBUG_LINES, log_filename))
+                    for line in lines[-LOG_DEBUG_LINES:]:
+                        logging.debug('>>> {}'.format(line))
             if args.keep_going:
                 failed_builds.append(build_info)
             else:

tools/ci/mypy_ignore_list.txt

@@ -153,7 +153,6 @@ examples/wifi/iperf/iperf_test.py
 tools/ble/lib_ble_client.py
 tools/ble/lib_gap.py
 tools/ble/lib_gatt.py
-tools/build_apps.py
 tools/check_python_dependencies.py
 tools/check_term.py
 tools/ci/check_artifacts_expire_time.py