terminal: disable terminal progress plugin on iTerm2

[bluetech]

Fix #13896

[webknjaz]

This feels overly nested. How about

Suggested change

	if reporter.isatty():
	plugin = TerminalProgressPlugin(reporter)
	config.pluginmanager.register(plugin, "terminalprogress")
	# Some terminals interpret OSC 9;4 as desktop notification,
	# skip on those we know (#13896).
	should_skip_terminal_progress = (
	# iTerm2 (reported on version 3.6.5).
	"ITERM_SESSION_ID" in os.environ
	)
	if not should_skip_terminal_progress:
	plugin = TerminalProgressPlugin(reporter)
	config.pluginmanager.register(plugin, "terminalprogress")
	# Some terminals interpret OSC 9;4 as desktop notification,
	# skip on those we know (#13896).
	should_skip_terminal_progress = (
	# iTerm2 (reported on version 3.6.5).
	"ITERM_SESSION_ID" in os.environ
	) or not reporter.isatty()
	if should_skip_terminal_progress:
	return
	plugin = TerminalProgressPlugin(reporter)
	config.pluginmanager.register(plugin, "terminalprogress")

?

[bluetech]

I prefer to avoid early return in hooks because it's possible we add more unrelated stuff to it in the future.

[webknjaz]

So

Suggested change

	if reporter.isatty():
	plugin = TerminalProgressPlugin(reporter)
	config.pluginmanager.register(plugin, "terminalprogress")
	# Some terminals interpret OSC 9;4 as desktop notification,
	# skip on those we know (#13896).
	should_skip_terminal_progress = (
	# iTerm2 (reported on version 3.6.5).
	"ITERM_SESSION_ID" in os.environ
	)
	if not should_skip_terminal_progress:
	plugin = TerminalProgressPlugin(reporter)
	config.pluginmanager.register(plugin, "terminalprogress")
	# Some terminals interpret OSC 9;4 as desktop notification,
	# skip on those we know (#13896).
	enable_terminal_progress = (
	# iTerm2 (reported on version 3.6.5).
	"ITERM_SESSION_ID" not in os.environ
	) and reporter.isatty()
	if enable_terminal_progress:
	plugin = TerminalProgressPlugin(reporter)
	config.pluginmanager.register(plugin, "terminalprogress")

then?

[bluetech]

It messes with the comment a bit. The isatty is the more important check, but I want to have a dedicated comment for the entire "unsupported terminals" check (in case we decide to add more cases).