Add str.to_quoted

[emersion]

Allow adding quotes to a string with a new str.to_quoted method. This would be useful for things like:

cargs = ['-DMY_VAR=@0@'.format(arbitrary_string.to_quoted())]

which would behave properly even if arbitrary_string contains a " or a \.

[xclaesse]

It would do python's shlex.quote() basically, right? aka shell escaping,

[xclaesse]

AFAIK, Meson will already shell quote every args it pass to the compiler for you. Have you tried and it does not work?

[emersion]

It would do python's shlex.quote() basically, right? aka shell escaping,

Yeah. Same as cfg_data.set_quoted().

AFAIK, Meson will already shell quote every args it pass to the compiler for you. Have you tried and it does not work?

Nah, this won't work, the value needs to be quoted as well for the C parser to recognize it as a C string and not another kind of literal. Example:

project('test', 'c')

myvar = 'a b " c'
add_project_arguments('-DMYVAR=' + myvar, language: 'c')

executable('main', 'main.c')

#include <stdio.h>

int main(void) {
	printf("MYVAR = %s\n", MYVAR);
}

[eli-schwartz]

Yeah. Same as cfg_data.set_quoted().

Configuration data uses C-style escaping, and the specific implementation details are:

• replace all double-quote chars with a backslash-escaped one
• double-quote the string

This is not what shlex does at all, because shells use different rules that need to account for pretty different things. Particularly worth noting is that shlex will not quote at all, if it is given a string that doesn't have any whitespace/quoting/shell special characters, e.g.

shlex.quote('foo') # -> foo
confdata.set_quoted('foo') # -> "foo"

[jpakkane]

As a general guide, try to avoid passing things via command line arguments. They are a constant source of trouble even when things are working. It is a lot easier to use a configuration header instead. Just the fact that you can debug its contents without needing to manually unwrap several layers of different quotings makes things so much simpler.

[emersion]

I would tend to agree, at least when -Wundef is enabled and #ifdef is not used (otherwise it's too easy to forget to include the config header). But note that there aren't more quoting levels when using CLI args. There is one level of quoting (for C strings) for each element in the argv array. Maybe ninja adds an additional level of quoting in its -v pretty-printing.

[xclaesse]

Ok, so here we talk about C string level quoting, not shlex, wasn't sure. Makes much more sense.

[eli-schwartz]

There is one level of quoting (for C strings) for each element in the argv array. Maybe ninja adds an additional level of quoting in its -v pretty-printing.

ninja runs in a shell, and meson writes out shell-escaped command lines. So there are two levels of quoting:

• the double quotes in the macro definition
• a pair of single quotes around the argv element

Plus whatever any unusual individual chooses to add in the string, because someone out there is totally going to do

'ab$\'c d"""!e'.to_quoted()

And expect it to work. They're also probably going to expect it to work regardless of whether it's being stuck in a c_args or formatted into run_command('sh', '-c', 'some complicated command'), because people do in fact actually do this and it's pain.

Spoiler: it won't work for both. :(

[emersion]

Oh. I didn't know ninja was dealing with sh. That's unfortunate.

Indeed, shell quoting doesn't work like C quoting. Would a function named to_c_quoted() to to_quoted(language: 'c') be any better?

Or something like add_project_define('MYVAR', value) which automatically escapes if the value is a string?