Set RUSTC and RUSTDOC env for child processes run through the proxy #2958
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This serves two purposes: 1. It avoids the overhead of having to re-parse `settings.toml` on each proxy. In projects with many crates, this can have non-trivial overhead. 2. For build scripts, it provides an absolute path for RUSTC rather than forcing them to look it up in PATH. This allows them to find the sysroot path for the toolchain, rather than ending up somewhere in CARGO_HOME. The original motivation for this was to allow `bootstrap` in rust-lang/rust to allow building stage0 tools without python, only the host rust toolchain.
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Ok, I found a better way to do this for bootstrap specifically: rust-lang/rust#94806. I do think it could be useful to set these variables though, the decreased build time especially seems tempting. |
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Are you confident this is right when using rustup to patch a rustc-only dev build with stable's cargo? |
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Yes. |
This was referenced Aug 17, 2022
ChrisDenton
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Aug 20, 2022
…enkov Add `rustc --print rustc-path` Related: - rust-lang/cargo#10986 - rust-lang/rustup#3035 Goal: Like the original rust-lang/rustup#2958, the goal is to enable `cargo` to call `rustc` directly, rather than through the `rustup` shim. Solution: `cargo` asks `rustc` to tell it what executable to run. Sometime early in compilation, `cargo` will run `$(RUSTC_WRAPPER) $(RUSTC ?: rustc) --print rustc-path`[^1]. Further calls to `rustc` to do execution will use the resolved printed executable path rather than continuing to call the "input `rustc` path," which will allow it to bypass the `rustup` shim. The cargo side is rust-lang/cargo#10998. [^1]: This can potentially be combined with other `--print`s, as well! This is a tiny patch, so I've implemented it as insta-stable; this will need signoff probably from both the compiler and cargo teams. I'm working on the cargo side of the patch currently, but wanted to get this up ASAP. cc `@davidlattimore` `@bjorn3` `@rust-lang/cargo` `@rust-lang/compiler` (sorry for the big ping list 😅)
matthiaskrgr
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Aug 21, 2022
…enkov Add `rustc --print rustc-path` Related: - rust-lang/cargo#10986 - rust-lang/rustup#3035 Goal: Like the original rust-lang/rustup#2958, the goal is to enable `cargo` to call `rustc` directly, rather than through the `rustup` shim. Solution: `cargo` asks `rustc` to tell it what executable to run. Sometime early in compilation, `cargo` will run `$(RUSTC_WRAPPER) $(RUSTC ?: rustc) --print rustc-path`[^1]. Further calls to `rustc` to do execution will use the resolved printed executable path rather than continuing to call the "input `rustc` path," which will allow it to bypass the `rustup` shim. The cargo side is rust-lang/cargo#10998. [^1]: This can potentially be combined with other `--print`s, as well! This is a tiny patch, so I've implemented it as insta-stable; this will need signoff probably from both the compiler and cargo teams. I'm working on the cargo side of the patch currently, but wanted to get this up ASAP. cc `@davidlattimore` `@bjorn3` `@rust-lang/cargo` `@rust-lang/compiler` (sorry for the big ping list 😅)
matthiaskrgr
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Aug 21, 2022
…enkov Add `rustc --print rustc-path` Related: - rust-lang/cargo#10986 - rust-lang/rustup#3035 Goal: Like the original rust-lang/rustup#2958, the goal is to enable `cargo` to call `rustc` directly, rather than through the `rustup` shim. Solution: `cargo` asks `rustc` to tell it what executable to run. Sometime early in compilation, `cargo` will run `$(RUSTC_WRAPPER) $(RUSTC ?: rustc) --print rustc-path`[^1]. Further calls to `rustc` to do execution will use the resolved printed executable path rather than continuing to call the "input `rustc` path," which will allow it to bypass the `rustup` shim. The cargo side is rust-lang/cargo#10998. [^1]: This can potentially be combined with other `--print`s, as well! This is a tiny patch, so I've implemented it as insta-stable; this will need signoff probably from both the compiler and cargo teams. I'm working on the cargo side of the patch currently, but wanted to get this up ASAP. cc ``@davidlattimore`` ``@bjorn3`` ``@rust-lang/cargo`` ``@rust-lang/compiler`` (sorry for the big ping list 😅)
matthiaskrgr
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Aug 21, 2022
…enkov Add `rustc --print rustc-path` Related: - rust-lang/cargo#10986 - rust-lang/rustup#3035 Goal: Like the original rust-lang/rustup#2958, the goal is to enable `cargo` to call `rustc` directly, rather than through the `rustup` shim. Solution: `cargo` asks `rustc` to tell it what executable to run. Sometime early in compilation, `cargo` will run `$(RUSTC_WRAPPER) $(RUSTC ?: rustc) --print rustc-path`[^1]. Further calls to `rustc` to do execution will use the resolved printed executable path rather than continuing to call the "input `rustc` path," which will allow it to bypass the `rustup` shim. The cargo side is rust-lang/cargo#10998. [^1]: This can potentially be combined with other `--print`s, as well! This is a tiny patch, so I've implemented it as insta-stable; this will need signoff probably from both the compiler and cargo teams. I'm working on the cargo side of the patch currently, but wanted to get this up ASAP. cc ```@davidlattimore``` ```@bjorn3``` ```@rust-lang/cargo``` ```@rust-lang/compiler``` (sorry for the big ping list 😅)
matthiaskrgr
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that referenced
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Aug 21, 2022
…enkov Add `rustc --print rustc-path` Related: - rust-lang/cargo#10986 - rust-lang/rustup#3035 Goal: Like the original rust-lang/rustup#2958, the goal is to enable `cargo` to call `rustc` directly, rather than through the `rustup` shim. Solution: `cargo` asks `rustc` to tell it what executable to run. Sometime early in compilation, `cargo` will run `$(RUSTC_WRAPPER) $(RUSTC ?: rustc) --print rustc-path`[^1]. Further calls to `rustc` to do execution will use the resolved printed executable path rather than continuing to call the "input `rustc` path," which will allow it to bypass the `rustup` shim. The cargo side is rust-lang/cargo#10998. [^1]: This can potentially be combined with other `--print`s, as well! This is a tiny patch, so I've implemented it as insta-stable; this will need signoff probably from both the compiler and cargo teams. I'm working on the cargo side of the patch currently, but wanted to get this up ASAP. cc ````@davidlattimore```` ````@bjorn3```` ````@rust-lang/cargo```` ````@rust-lang/compiler```` (sorry for the big ping list 😅)
bors
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May 4, 2023
Optimize usage under rustup. Closes #10986 This optimizes cargo when running under rustup to circumvent the rustup proxies. The rustup proxies introduce overhead that can make a noticeable difference. The solution here is to identify if cargo would normally run `rustc` from PATH, and the current `rustc` in PATH points to something that looks like a rustup proxy (by comparing it to the `rustup` binary which is a hard-link to the proxy). If it detects this situation, then it looks for a binary in `$RUSTUP_HOME/toolchains/$TOOLCHAIN/bin/$TOOL`. If it finds the direct toolchain executable, then it uses that instead. ## Considerations There have been some past attempts in the past to address this, but it has been a tricky problem to solve. This change has some risk because cargo is attempting to guess what the user and rustup wants, and it may guess wrong. Here are some considerations and risks for this: * Setting `RUSTC` (as in rust-lang/rustup#2958) isn't an option. This makes the `RUSTC` setting "sticky" through invocations of different toolchains, such as a cargo subcommand or build script which does something like `cargo +nightly build`. * Changing `PATH` isn't an option, due to issues like rust-lang/rustup#3036 where cargo subcommands would be unable to execute proxies (so things like `+toolchain` shorthands don't work). * Setting other environment variables in rustup (as in rust-lang/rustup#3207 which adds `RUSTUP_TOOLCHAIN_DIR` the path to the toolchain dir) comes with various complications, as there is risk that the environment variables could get out of sync with one another (like with `RUSTUP_TOOLCHAIN`), causing tools to break or become confused. There was some consideration in that PR for adding protections by using an encoded environment variable that could be cross-checked, but I have concerns about the complexity of the solution. We may want to go with this solution in the long run, but I would like to try a short term solution in this PR first to see how it turns out. * This won't work for a `rustup-toolchain.toml` override with a [`path`](https://rust-lang.github.io/rustup/overrides.html#path) setting. Cargo will use the slow path in that case. In theory it could try to detect this situation, which may be an exercise for the future. * Some build-scripts, proc-macros, or custom cargo subcommands may be doing unusual things that interfere with the assumptions made in this PR. For example, a custom subcommand could call a `cargo` executable that is not managed by rustup. Proc-macros may be executing cargo or rustc, assuming it will reach some particular toolchain. It can be difficult to predict what unusual ways cargo and rustc are being used. This PR (and its tests) tries to make extra sure that it is resilient even in unusual circumstances. * The "dev" fallback in rustup can introduce some complications for some solutions to this problem. If a rustup toolchain does not have cargo, such as with a developer "toolchain link", then rustup will automatically call either the nightly, beta, or stable cargo if they are available. This PR should work correctly, since rustup sets the correct `RUSTUP_TOOLCHAIN` environment variable for the *actual* toolchain, not the one where cargo was executed from. * Special care should be considered for dynamic linking. `LD_LIBRARY_PATH` (linux), `DYLD_LIBRARY_PATH` (macos), and `PATH` (windows) need to be carefully set so that `rustc` can find its shared libraries. Directly executing `rustc` has some risk that it will load the wrong shared libraries. There are some mitigations for this. macOS and Linux use rpath, and Windows looks in the same directory as `rustc.exe`. Also, rustup configures the dyld environment variables from the outer cargo. Finally, cargo also configures these (particularly for the deprecated compiler plugins). * This shouldn't impact installations that don't use rustup. * I've done a variety of testing on the big three platforms, but certainly nowhere exhaustive. * One of many examples is making sure Clippy's development environment works correctly, which has special requirements for dynamic linking. * There is risk about future rustup versions changing some assumptions made here. Some assumptions: * It assumes that if `RUSTUP_TOOLCHAIN` is set, then the proxy *always* runs exactly that toolchain and no other. If this changes, cargo could execute the wrong version. Currently `RUSTUP_TOOLCHAIN` is the highest priority [toolchain override](https://rust-lang.github.io/rustup/overrides.html) and is fundamental to how toolchain selection becomes "sticky", so I think it is unlikely to change. * It assumes rustup sets `RUSTUP_TOOLCHAIN` to a value that is exactly equal to the name of the toolchain in the `toolchains` directory. This works for user shorthands like `RUSTUP_TOOLCHAIN=nightly`, which gets converted to the full toolchain name. However, it does not work for `path` overrides (see above). * It assumes the `toolchains` directory layout is always `$RUSTUP_HOME/toolchains/$TOOLCHAIN`. If this changes, then I think the only consequence is that cargo will go back to the slow path. * It assumes downloading toolchains is not needed (since cargo running from the toolchain means it should already be downloaded). * It assumes there is no other environment setup needed (such as the dyld paths mentioned above). My hope is that if assumptions are no longer valid that the worst case is that cargo falls back to the slow path of running the proxy from PATH. ## Performance This change won't affect the performance on Windows because rustup currently alters PATH to point to the toolchain directory. However, rust-lang/rustup#3178 is attempting to remove that, so this PR will be required to avoid a performance penalty on Windows. That change is currently opt-in, and will likely take a long while to roll out since it won't be released until after the next release, and may be difficult to get sufficient testing. I have done some rough performance testing on macOS, Windows, and Linux on a variety of different kinds of projects with different commands. The following attempts to summarize what I saw. The timings are going to be heavily dependent on the system and the project. These are the values I get on my systems, but will likely be very different for everyone else. The Windows tests were performed with a custom build of rustup with rust-lang/rustup#3178 applied and enabled (stock rustup shows no change in performance as explained above). The data is summarized in this spreadsheet: https://docs.google.com/spreadsheets/d/1zSvU1fQ0uSELxv3VqWmegGBhbLR-8_KUkyIzCIk21X0/edit?usp=sharing `hello-world` has a particularly large impact of about 1.68 to 2.7x faster. However, a large portion of this overhead is related to running `rustc` at the start to discover its version and querying it for information. This is cached after the first run, so except for first-time builds, the effect isn't as noticeable. The "check with info" row is an benchmark that removes `target/debug/deps` but keeps the `.rustc_info.json` file. Incremental builds are a bit more difficult to construct since it requires customizing the commands for each project. I only did an incremental test for cargo itself, running `touch src/cargo/lib.rs` and then `cargo check --lib`. These measurements excluded the initial overhead of launching the rustup proxy to launch the initial cargo process. This was done just for simplicity, but it makes the test a little less characteristic of a typical usage, which will have some constant overhead for running the proxy. These tests were done using [`hyperfine`](https://crates.io/crates/hyperfine) version 1.16.1. The macOS system was an M2 Max (12-thread). The Windows and Linux experiments were run on a AMD Ryzen Threadripper 2950X (32-thread). Rust 1.68.2 was used for testing. I can share the commands if people want to see them.
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This serves two purposes:
settings.tomlon each proxy.In projects with many crates, this can have non-trivial overhead.
This allows them to find the sysroot path for the toolchain, rather than ending up somewhere in CARGO_HOME.
The original motivation for this was to allow
bootstrapin rust-lang/rustto allow building stage0 tools without python, only the host rust toolchain. See rust-lang/rust#94797.
cc @Mark-Simulacrum - do you think this is a reasonable approach to fixing the original issue? It does have the downside that we can't fix it until ~the next rustup release, but I think it's the least hacky way to do it. Other things I can think of involve running
rustup which rustcand such, which seems pretty not great if we don't know whetherrustcis managed by rustup or not.Reverted in #3034.