[bug] MesonToolchain: project options of type string are not quoted (ERROR: Malformed value in machine file variable)

[SpaceIm]

Environment details

• Operating System+version: macOS Ventura
• Compiler+version: apple clang 14
• Conan version: 2.0.9
• Python version: 3.11.4

Steps to reproduce

Create a conan recipe based on Meson, and pass a recipe option of type ["ANY"] (with a string as default_options) to project_options.

For example:

options = {
    "foo": ["ANY"],
    "bar": ["ANY"],
}
default_options = {
    "foo": "/var/run/foo",
    "bar": "BAR",
}

(...)

tc = MesonToolchain(self)
tc.project_options["foo"] = self.options.foo
tc.project_options["bar"] = self.options.bar
tc.generate()

The problem is that values are not quoted in generated machine file. Surprisingly, they are quoted if value is passed directly tc.project_options["foo"] = "/var/run/foo", I guess there is something wrong when self.options.foo is resolved.

(I'm not sure, but for the fix you likely want to avoid to quote boolean options)

Logs

First option gives this error:

ERROR: Malformed value in machine file variable 'foo': Unsupported node type.

Second option gives this error:

ERROR: Undefined constant 'BAR' in machine file variable 'bar'.

[SpaceIm]

As a workaround, I pass str(self.options.foo) to project_options, so that to_meson_value() can go into the branch isinstance(value, str).

EDIT: see conan-io/conan-center-index#19115