Source-only introspection ignores default_options passed to subprojects

[MaxandreOgeret]

Describe the bug
Source-only introspection (meson introspect --buildoptions meson.build, without a configured build dir) lists subproject options with the subproject's own default values, ignoring values the parent project passes down via default_options (either in the subproject() call or as sub:opt=... in the project() call).

The IntrospectionInterpreter (mesonbuild/ast/introspection.py) collects option definitions from each subproject but never applies the parent's default_options, unlike the real interpreter which resolves them via initialize_from_subproject_call(). After a real meson setup, introspection from the build dir reports the correct value.

To Reproduce

mkdir -p repro/subprojects/sub && cd repro
cat > meson.build <<'MESON'
project('main', 'c')
subproject('sub', default_options: ['myopt=fromparent'])
MESON
cat > subprojects/sub/meson.build <<'MESON'
project('sub', 'c')
MESON
cat > subprojects/sub/meson_options.txt <<'MESON'
option('myopt', type: 'string', value: 'default')
MESON
meson introspect --buildoptions meson.build
# reports sub:myopt = "default"

meson setup build
meson introspect --buildoptions build
# reports sub:myopt = "fromparent" (correct)

Expected behavior
Source-only introspection reports the value that a real configuration would use, i.e. sub:myopt = fromparent.

system parameters

• Plain native build
• Debian GNU/Linux (forky/sid)
• Python 3.13.14
• meson 1.10.0, also reproduced on current master (1.12.0.rc1, 2b4f5dc)
• ninja 1.13.2 (not relevant, no build dir needed)

[MaxandreOgeret]

@bonzini should i close my PR? #15995

[bonzini]

No, why? It was on my list to check, at the very least it has good tests.

However, can you rebase it and remove the release notes from it?

[MaxandreOgeret]

Because this merged PR #16080 closed this issue. I actually did not dig into the changes.
I will look at the code and see what needs to be done still.

[bonzini]

Your PR closes #15993 not this one.