This removes a bunch of manual filesystem helpers and complexity that
are directly provided by the new library.
It also moves all of the install paths detection to use
`std::filesystem::path` instead of the LLVM path library. The goal is to
consolidate all our logic onto a single stack, and the standard one
seems the best for that purpose. This does give up some of the
optimizations of this code to avoid memory allocation, but in practice
that likely isn't a critical issue. And with the new filesystem library
we can likely do more to avoid that by using directory-object-relative
filesystem access. However, that will have to wait for moving more parts
of the toolchain over to use this set of filesystem abstractions. There
is a related TODO left in the manifest handling code.
When finding an executable, this validates that the returned binary is a
symlink back to the same thing as /proc/self/exe, also using that as a
fallback for different things.
Looking back at #3912, we started using `findProgramByName` in order to
avoid path canonicalization done by `GetMainExecutable`. That created
issues as in #5096, wherein an `argv[0]` that's not explicit enough
(`llvm-symbolizer` instead of the full path, done in [LLVM's
Signals.cpp](https://github.com/llvm/llvm-project/blob/4f60f45130c6bd96c79e468fe9927a29af760f56/llvm/lib/Support/Signals.cpp#L198))
leads to incorrect results (finding an `llvm-symbolizer` in `$PATH`).
One option to fix this would be to patch LLVM to provide an absolute
path for `llvm-symbolizer`. However, I'll suggest that passing a
filename in `argv[0]` is not terribly uncommon, and could be a migration
limitation if we force it. The failure mode is also opaque; for example:
```
$ /bin/sh -c "exec -a llvm-symbolizer ./bazel-bin/toolchain/carbon"
error: expected carbon-busybox symlink at `/usr/lib/llvm-19/bin/llvm-symbolizer`
```
Combined with the `setenv` of `LLVM_SYMBOLIZER_PATH` in
`busybox_main.cpp`, this is intended to fix#5096.
Both of these I noticed from testing #4785, but they occur at head.
```
(elided)/execroot/_main/common/raw_hashtable.h:532:40: error: do not use nested 'std::max' calls, use an initializer list instead [modernize-min-max-use-initializer-list,-warnings-as-errors]
532 | static constexpr ssize_t Alignment = std::max<ssize_t>(
| ^
533 | {alignof(MetadataGroup), alignof(StorageEntry<KeyT, ValueT>)});
| ~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| static_cast<long>(alignof(MetadataGroup)) static_cast<long>(alignof(StorageEntry<KeyT, ValueT>))
(elided)/execroot/_main/toolchain/install/busybox_info_test.cpp:259:8: error: unused local variable 'usr_prefix' of type 'std::filesystem::path' [bugprone-unused-local-non-trivial-variable,-warnings-as-errors]
259 | auto usr_prefix = MakeInstallTree(dir_ / "usr");
| ^
(elided)/execroot/_main/toolchain/install/busybox_info_test.cpp:260:8: error: unused local variable 'usr_local_prefix' of type 'std::filesystem::path' [bugprone-unused-local-non-trivial-variable,-warnings-as-errors]
260 | auto usr_local_prefix = MakeInstallTree(dir_ / "usr/local");
| ^
```
The std::max diagnostic seems a little confused, but the initializer
list seems like it can be dropped without any loss. The unused locals
diagnostic is correct.
Neither of these seem like they should be newer than my last clang-tidy
pass, maybe I just missed them in other sweeps.
This restores the symlinks for the installation, but teaches the busybox
info search to look for a relative path to the busybox binary itself
before walking through symlinks. This let's it find the tree structure
when directly invoking `prefix_root/bin/carbon` or similar, either
inside of a Bazel rule or from the command line, and mirrors how we
expect the installed tree to look. This works even when Bazel resolves
the symlink target fully, and potentially to something nonsensical like
a CAS file.
In order to make a convenient Bazel target that can be used with `bazel
run //toolchain`, this adds an override to explicitly set the desired
argv[0] to use when selecting a mode for the busybox and a busybox
binary. Currently, the workaround uses an environment variable because
that required the least amount of plumbing, and seems a useful override
mechanism generally, but I'm open to other approaches.
This should allow a few things to work a bit more nicely:
- It should handle sibling symlinks like `clang++` to `clang` or
`ld.lld` to `lld`, where that symlink in turn points at the busybox.
We want to use *initial* `argv[0]` value to select the mode there.
- It avoids bouncing through Python (or other subprocesses) when
invoking the `carbon` binary in Bazel rules, which will be nice for
building the example code and benchmarking.
It does come at a cost of removing one feature: the initial symlink
can't be some unrelated alias like `my_carbon_symlink` -- we expect the
*first* argv[0] name to have the meaningful filename for selecting
a busybox mode.
It also trades the complexity of the Python script for some complexity
in the busybox search in order to look for a relative `carbon-busybox`
binary. On the whole, I think that tradeoff is worthwhile, but it isn't
free.
---------
Co-authored-by: Jon Ross-Perkins <jperkins@google.com>
Pursuant to discussion regarding #4699, turn on
`misc-non-private-member-variables-in-classes` using the
`IgnoreClassesWithAllMemberVariablesBeingPublic` flag (the check treats
structs as classes, so we need this for structs with all-public
members). Updates the style guide notes to match, which should be pretty
minor due to the scoping of test fixtures.
Also fixes some underscore uses in test files on the way. Basically this
is keeping the style for [class data member
naming](https://google.github.io/styleguide/cppguide.html#Variable_Names)
even while making them public.
Chandler Carruth
Jon Ross-Perkins
Thomas Köppe