Cross file whitespace parsing error

[codido]

A parsing error is thrown if a closing bracket in a cross file appears at the beginning of the line.

For example, this works:

c_args = [
    '-DFOO'
    ]

...but this doesn't:

c_args = [
    '-DFOO'
]

[Salamandar]

I can confirm the bug still exists.

Traceback (most recent call last):
  File "/usr/lib/python3.7/site-packages/mesonbuild/mesonmain.py", line 112, in run
    return options.run_func(options)
  File "/usr/lib/python3.7/site-packages/mesonbuild/msetup.py", line 230, in run
    app.generate()
  File "/usr/lib/python3.7/site-packages/mesonbuild/msetup.py", line 156, in generate
    env = environment.Environment(self.source_dir, self.build_dir, self.options)
  File "/usr/lib/python3.7/site-packages/mesonbuild/environment.py", line 359, in __init__
    self.cross_info = CrossBuildInfo(self.coredata.cross_file)
  File "/usr/lib/python3.7/site-packages/mesonbuild/environment.py", line 1107, in __init__
    self.parse_datafile(filename)
  File "/usr/lib/python3.7/site-packages/mesonbuild/environment.py", line 1120, in parse_datafile
    config.read_file(f, filename)
  File "/usr/lib/python3.7/configparser.py", line 717, in read_file
    self._read(f, source)
  File "/usr/lib/python3.7/configparser.py", line 1110, in _read
    raise e
configparser.ParsingError: Source contains parsing errors: '/home/salamandar/phenix/stm32-template/stm32f303.meson'
    [line 29]: ']\n'
    [line 35]: ']\n'
    [line 41]: ']\n'

[bdsbdsbds]

This has been annoying me so I looked into it, and I believe this is because Meson is just using Python's default configparser module, which doesn't actually have a concept of a list. Instead, everything is just a string. Multiline values are accepted, but only so long as they are also indented, which is why having an ending bracket on an unindented line doesn't work. After looking at the documentation for configparser, supporting lists seems completely out of scope, so it seems like if Meson wants to properly support lists in cross files, it would need an actual parser for them.

[Salamandar]

Why not use the actual meson parser, but with "forbidden values", just like for the meson_options.txt file ? That would allow "variables" like :

c_args = […]

cpp_args = c_args + […]

[bdsbdsbds]

That seems like a much better idea. I didn't realize that the regular meson parser was already being used for parsing things other than just meson.build files. Unifying the allowed syntax as much as possible with meson.build seems ideal.