ldionne added subscribers: libc++, libc++ vendors, rsmith, CaseyCarter.
ldionne added a comment.
Oops, this seems to have happened while I was on vacation. I wanted to have a
wider discussion here before shipping the patch. Let's have it now and we can
make post-commit changes depending on where the discussion leads.
So, what we're trying to achieve here is to provide a user-controlled flag to
enable things that are not "production ready". This includes:
- TSes (since we remove them after shipping the "real thing" for two releases)
- Standardized features that we implement only in part (for example `<ranges>`,
where we don't yet have a fully coherent thing to ship, so we'd rather not
pretend that we ship it in a stable way yet)
- Standardized features that we know for a fact are about to be broken by the
Standard itself (this happened with `<ranges>` and `<format>` recently)
The problem this solves is that in the current state of things, we end up
simply not shipping those features at all by fear that users are going to start
depending on them, and then we'll break them. We want to be able to ship these
features without actually committing to their stability.
We considered a few alternative directions for this patch, which we rejected:
- `-fexperimental`: We decided not to go with this because we wanted to convey
the fact that said features were unstable, and hence dangerous to use in
production code
- `-std=c++latest`: This would be close to what MSVC does. We decided not to go
down this route because we felt like it didn't properly convey the notion of
instability. Instead, we felt that `-std=c++latest` could/should be a simple
alias for whatever the latest known standard is (which is not part of this
patch).
Does anyone have thoughts?
================
Comment at: clang/include/clang/Basic/LangOptions.def:153
LANGOPT(RelaxedTemplateTemplateArgs, 1, 0, "C++17 relaxed matching of template
template arguments")
+LANGOPT(Unstable , 1, 0, "Enable unstable and experimental features")
----------------
The documentation of this option should be way more beefy. Something like:
```
Enable unstable and experimental language and library features.
This option enables various language and library features that are either
experimental (also known as TSes), or have been standardized but are not stable
yet. This option should not be used in production code, since neither ABI nor
API stability are guaranteed.
```
We should also provide documentation inside
`clang/docs/ClangCommandLineReference.rst`.
================
Comment at: clang/lib/Driver/ToolChains/Clang.cpp:5771
+ CmdArgs.push_back("-fcoroutines-ts");
+ CmdArgs.push_back("-fmodules-ts");
+ }
----------------
We should also be adding `-lc++experimental` if the standard library is libc++.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D120160/new/
https://reviews.llvm.org/D120160
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