No way to pass multiple values to list-like `--config` options

[jaybosamiya]

There appears to be no way to pass multiple values to a configuration parameter such as skip_macro_invocations from the command-line:

$ rustfmt --config 'skip_macro_invocations=["foo","bar"]'
invalid key=val pair: `skip_macro_invocations=["foo"`

$ rustfmt '--config=skip_macro_invocations=["foo","bar"]'
invalid key=val pair: `skip_macro_invocations=["foo"`

I believe this is due to the immediate split of the argument done here:

rustfmt/src/bin/main.rs

Lines 572 to 577 in 21f353a

	options.inline_config = matches
	.opt_strs("config")
	.iter()
	.flat_map(|config| config.split(','))
	.map(
	|key_val| match key_val.char_indices().find(|(_, ch)| *ch == '=') {

[ytmimi]

Thanks for the report. Going to link to the tracking issue for skip_macro_invocations #5346