# Objective
Running `cargo ci` on Fedora 40 causes a system crash due to many `ld`
processes consuming all available memory when performing doc tests.
## Solution
This PR extends #13553.
- Add reference to #12207 in the CI sections of `CONTRIBUTING.md` and
`config_fast_builds.toml`.
- Add sample `rustdocflags` configurations for `lld` and `mold` to
`config_fast_builds.toml` for Linux.
## Testing
Crashing configuration
- config.toml
```
[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = ["-Clink-arg=-fuse-ld=lld"]
[alias]
ci = "run --package ci --"
```
- Test command
`cargo ci`
Working configuration
- config.toml
```
[target.x86_64-unknown-linux-gnu]
linker = "clang"
rustflags = ["-Clink-arg=-fuse-ld=lld"]
rustdocflags = ["-Clink-arg=-fuse-ld=lld"]
[alias]
ci = "run --package ci --"
```
- Test command
`cargo ci`
# Objective
- Rustdoc doesn't seem to follow cargo's `linker` setting
- Improves the situation in #12207
## Solution
- Explicitly set the linker in rustdoc flags
## Testing
- I tested this change on Windows and it significantly improves testing
performances (can't give an exact estimate since they got stuck before
this change)
---
Note: I avoided changing the settings on Linux and MacOS because I can't
test on those platforms. It would be nice if someone could test similar
changes there and report so they can be done on all major platforms.
# Objective
- https://github.com/bevyengine/bevy/pull/13136 changed the default
value of `-Zshare-generics=n` to `-Zshare-generics=y` on Windows
- New users are encouraged to use dynamic builds and LLD when setting up
Bevy
- New users are also encouraged to check out `fast_config.toml`
- https://github.com/bevyengine/bevy/issues/1126 means that running
dynamic builds, using LLD and sharing generics on Windows results in a
cryptic error message
As a result, a new Windows user following all recommendations for better
compiles is actually not able to compile Bevy at all.
## Solution
- Set `-Zshare-generics=n` on Windows with a comment saying this is for
dynamic linking
## Testing
I verified that https://github.com/bevyengine/bevy/issues/1126 is still
in place on the current nightly (1.80)
## Additional Info
Maybe the website should mention this as well? The relevant snippet
there looks like this:
```toml
# /path/to/project/.cargo/config.toml
[target.x86_64-unknown-linux-gnu]
rustflags = [
# (Nightly) Make the current crate share its generic instantiations
"-Zshare-generics=y",
]
```
so it kinda implies it's only for Linux? Which is not quite true, this
setting works on macOS as well AFAIK
# Objective
- Running `cargo run --package ci -- ...` is lengthy, and `cargo r -p ci
-- ...` isn't much better.
- Closes#13197.
## Solution
- Add an opt-in alias to the `ci` tool with `cargo ci ...`.
- You need to copy `config_fast_builds.toml` to `config.toml` to enable
this functionality.
## Testing
- Copy `config_fast_builds.toml` to `config.toml`, then run `cargo ci
--help`.
---
## Changelog
- Added `cargo ci` alias for internal `ci` tool.
# Objective
- `config_fast_builds.toml` could use some general improvements and
additions.
- [Mold](https://github.com/rui314/mold) is a modern linker with serious
performance improvements that provides a good alternative to LLD.
- This is exactly the same as #12949; I accidentally deleted the branch.
😅
## Solution
- Majorly improve `config_fast_builds.toml`.
- Add further documentation.
- Add a section for the alternative Mold linker, which is **much**
faster.
- Disable nightly options by default so that developers running stable
can copy the file without having to edit it. (Nightly is still
recommended, but this is following suite with `rustfmt.toml`.)
---
## Changelog
- Majorly improved `config_fast_builds.toml` documentation and added
Mold linker.
# Objective
- The build on Windows currently fails on stable when using the
`config.toml` as described but commenting out all lines that say
"Nightly"
## Solution
- Add a missing nightly specifier for a flag that won't run on stable
# Objective
Improve compile times.
## Solution
The `-Z threads=0` option has been introduced into nightly rust somewhat
recently, and was showcased in this [rust-lang
article](https://blog.rust-lang.org/2023/11/09/parallel-rustc.html).
This option improves multithreading in rust and speeds up compilation. I
added this option to `config_fast_builds.toml` so others can also use
this option to improve compile times.
`-Z threads=0` automatically uses the same amount of threads as the
amount of threads in your system (See [rustc source
code](6b4f1c5e78/compiler/rustc_session/src/options.rs (L617))).
### Benchmarks
> **Disclaimer:** This section was written before I knew of `-Z
threads=0`, so it uses `-Z threads=8` instead.
I compiled bevy with/without the `-Z threads=8` and saw about a 7%
improvement in compliation times on my Kubuntu system with a 13th Gen
Intel® Core™ i5-13400.
Also the compile times go down over time, probably because I had other
things running in the background.
#### Without `-Z threads=8`
- 42.33s
- 40.90s
- 38.27s
- 38.07s
- 37.17s
- 37.67s
- 36.63s
- 37.24s
**Average**: 38.535
#### With `-Z threads=8`
- 36.77s
- 39.50s
- 38.86s
- 35.61s
- 34.37s
- 34.32s
- 34.44s
- 33.74s
**Average**: 35.95125
# Objective
Theres no explaination for what the compiler flags
`config_fast_builds.toml` do
## Solution
Explain what the flags in `config_fast_builds.toml` do.
