Bug 985857 - Automatically log mach output and add a command to display it. r=gps

python/mozbuild/mozbuild/base.py

@@ -700,6 +700,20 @@ class MachCommandBase(MozbuildObject):
 
             sys.exit(1)
 
+        # Always keep a log of the last command, but don't do that for mach
+        # invokations from scripts (especially not the ones done by the build
+        # system itself).
+        if (self.log_manager and self.log_manager.terminal and
+                not getattr(self, 'NO_AUTO_LOG', False)):
+            self._ensure_state_subdir_exists('.')
+            logfile = self._get_state_filename('last_log.json')
+            try:
+                fd = open(logfile, "wb")
+                self.log_manager.add_json_handler(fd)
+            except Exception as e:
+                self.log(logging.WARNING, 'mach', {'error': e},
+                         'Log will not be kept for this command: {error}.')
+
 
 class MachCommandConditions(object):
     """A series of commonly used condition functions which can be applied to

python/mozbuild/mozbuild/mach_commands.py

@@ -4,10 +4,13 @@
 
 from __future__ import print_function, unicode_literals
 
+import argparse
 import itertools
+import json
 import logging
 import operator
 import os
+import subprocess
 import sys
 
 import mozpack.path as mozpath
@@ -566,6 +569,65 @@ class Doctor(MachCommandBase):
         doctor = Doctor(self.topsrcdir, self.topobjdir, fix)
         return doctor.check_all()
 
+@CommandProvider
+class Logs(MachCommandBase):
+    """Provide commands to read mach logs."""
+    NO_AUTO_LOG = True
+
+    @Command('show-log', category='post-build',
+        description='Display mach logs')
+    @CommandArgument('log_file', nargs='?', type=argparse.FileType('rb'),
+        help='Filename to read log data from. Defaults to the log of the last '
+             'mach command.')
+    def show_log(self, log_file=None):
+        if not log_file:
+            path = self._get_state_filename('last_log.json')
+            log_file = open(path, 'rb')
+
+        if self.log_manager.terminal:
+            env = dict(os.environ)
+            if 'LESS' not in env:
+                # Sensible default flags if none have been set in the user
+                # environment.
+                env['LESS'] = 'FRX'
+            less = subprocess.Popen(['less'], stdin=subprocess.PIPE, env=env)
+            # Various objects already have a reference to sys.stdout, so we
+            # can't just change it, we need to change the file descriptor under
+            # it to redirect to less's input.
+            # First keep a copy of the sys.stdout file descriptor.
+            output_fd = os.dup(sys.stdout.fileno())
+            os.dup2(less.stdin.fileno(), sys.stdout.fileno())
+
+        startTime = 0
+        for line in log_file:
+            created, action, params = json.loads(line)
+            if not startTime:
+                startTime = created
+                self.log_manager.terminal_handler.formatter.start_time = \
+                    created
+            if 'line' in params:
+                record = logging.makeLogRecord({
+                    'created': created,
+                    'name': self._logger.name,
+                    'levelno': logging.INFO,
+                    'msg': '{line}',
+                    'params': params,
+                    'action': action,
+                })
+                self._logger.handle(record)
+
+        if self.log_manager.terminal:
+            # Close less's input so that it knows that we're done sending data.
+            less.stdin.close()
+            # Since the less's input file descriptor is now also the stdout
+            # file descriptor, we still actually have a non-closed system file
+            # descriptor for less's input. Replacing sys.stdout's file
+            # descriptor with what it was before we replaced it will properly
+            # close less's input.
+            os.dup2(output_fd, sys.stdout.fileno())
+            less.wait()
+
+
 @CommandProvider
 class Warnings(MachCommandBase):
     """Provide commands for inspecting warnings."""