This is because a dynamic_cast<nix::RootArgs *> of a (n-e-j) MyArgs
returns nullptr even though MyArgs has virtual nix::RootArgs as a
parent.
class MyArgs : virtual public nix::MixEvalArgs,
virtual public nix::MixCommonArgs,
virtual nix::RootArgs { ... };
So this should work right?? But it does not. We found out that it's
caused by -fvisibility=hidden in n-e-j, but honestly this code was bad
anyway.
The trivial solution is to simply stop relying on RTTI working properly
here, which is probably better OO architecture anyway. However, I am not
100% confident *this* is sound, since we have this horrible hierarchy:
Args (defines getRoot)
/ | \
RootArgs MixCommonArgs MixEvalArgs
(overrides)
I am not confident that this is guaranteed to resolve from Args always
in the case of this override.
Assertion failed: (res), function getRoot, file src/libutil/args.cc, line 67.
6MyArgsProcess 60503 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = hit program assert
frame #4: 0x0000000100b1a41c liblixutil.dylib`nix::Args::processArgs(std::__1::list<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>, std::__1::allocator<std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char>>>> const&, bool) [inlined] nix::Args::getRoot(this=0x00000001000d0688) at args.cc:67:5 [opt]
64 std::cout << typeid(*p).name();
65
66 auto * res = dynamic_cast<RootArgs *>(p);
-> 67 assert(res);
68 return *res;
69 }
70
Target 0: (nix-eval-jobs) stopped.
(lldb) p this
(MyArgs *) 0x00000001000d0688
(lldb) p *this
(nix::Args) {
longFlags = size=180 { ... }
shortFlags = size=4 { ... }
expectedArgs = size=1 { ... }
processedArgs = size=0 {}
hiddenCategories = size=1 {
[0] = "Options to override configuration settings"
}
parent = nullptr
}
We also found that if we did this:
class [[gnu::visibility("default")]] RootArgs : virtual public Args
it would work properly (???!). This is of course, very strange, because
objdump -Ct output on liblixexpr.dylib is identical both with and
without it.
Possibly related: https://www.qt.io/blog/quality-assurance/one-way-dynamic_cast-across-library-boundaries-can-fail-and-how-to-fix-it
Fixes: lix-project/nix-eval-jobs#2
Change-Id: I6b9ed968ed56420a9c4d2dffd18999d78c2761bd
As I complained in
https://github.com/NixOS/nix/pull/6784#issuecomment-1421777030 (a
comment on the wrong PR, sorry again!), #6693 introduced a second
completions mechanism to fix a bug. Having two completion mechanisms
isn't so nice.
As @thufschmitt also pointed out, it was a bummer to go from `FlakeRef`
to `std::string` when collecting flake refs. Now it is `FlakeRefs`
again.
The underlying issue that sought to work around was that completion of
arguments not at the end can still benefit from the information from
latter arguments.
To fix this better, we rip out that change and simply defer all
completion processing until after all the (regular, already-complete)
arguments have been passed.
In addition, I noticed the original completion logic used some global
variables. I do not like global variables, because even if they save
lines of code, they also obfuscate the architecture of the code.
I got rid of them moved them to a new `RootArgs` class, which now has
`parseCmdline` instead of `Args`. The idea is that we have many argument
parsers from subcommands and what-not, but only one root args that owns
the other per actual parsing invocation. The state that was global is
now part of the root args instead.
This did, admittedly, add a bunch of new code. And I do feel bad about
that. So I went and added a lot of API docs to try to at least make the
current state of things clear to the next person.
--
This is needed for RFC 134 (tracking issue #7868). It was very hard to
modularize `Installable` parsing when there were two completion
arguments. I wouldn't go as far as to say it is *easy* now, but at least
it is less hard (and the completions test finally passed).
Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
Change-Id: If18cd5be78da4a70635e3fdcac6326dbfeea71a5
(cherry picked from commit 67eb37c1d0de28160cd25376e51d1ec1b1c8305b)
jade
