logging: Print location of log file on error

Similar to configure

Closes https://github.com/mesonbuild/meson/issues/2316

mesonbuild/mesonmain.py

@@ -340,7 +340,7 @@ def run(args, mainfile=None):
             dir2 = '.'
     try:
         if mainfile is None:
-            sys.exit('I iz broken. Sorry.')
+            raise AssertionError('I iz broken. Sorry.')
         app = MesonApp(dir1, dir2, mainfile, handshake, options, sys.argv)
     except Exception as e:
         # Log directory does not exist, so just print
@@ -356,7 +356,11 @@ def run(args, mainfile=None):
                 mlog.log(mlog.red('\nMeson encountered an error in file %s, line %d, column %d:' % (e.file, e.lineno, e.colno)))
             else:
                 mlog.log(mlog.red('\nMeson encountered an error:'))
+            # Error message
             mlog.log(e)
+            # Path to log file
+            logfile = os.path.join(app.build_dir, environment.Environment.log_dir, mlog.log_fname)
+            mlog.log("\nA full log can be found at", mlog.bold(logfile))
             if os.environ.get('MESON_FORCE_BACKTRACE'):
                 raise
         else:

mesonbuild/mlog.py

@@ -22,11 +22,12 @@ colorize_console = platform.system().lower() != 'windows' and os.isatty(sys.stdo
     os.environ.get('TERM') != 'dumb'
 log_dir = None
 log_file = None
+log_fname = 'meson-log.txt'
 
 def initialize(logdir):
     global log_dir, log_file
     log_dir = logdir
-    log_file = open(os.path.join(logdir, 'meson-log.txt'), 'w', encoding='utf8')
+    log_file = open(os.path.join(logdir, log_fname), 'w', encoding='utf8')
 
 def shutdown():
     global log_file