Auto merge of #2564 - RalfJung:no-more-xargo, r=oli-obk

use rustc-build-sysroot instead of xargo

This uses my crate https://github.com/RalfJung/rustc-build-sysroot instead of xargo to do the sysroot builds. That has the advantage of simplifying the Miri setup process and saving significant amounts of CI time for Miri users (since they don't have to build xargo from source all the time). Also xargo has a lot more functionality than we need so this should be easier to maintain and tweak for our needs.

With this, Miri no longer honors the `XARGO_RUST_SRC` env var to determine where the standard library sources are taken from. The README anyway says to use `MIRI_LIB_SRC` which will still work.

TODO:
- [x] add support for no-std targets
- [x] test that this works in the rustc repo

.github/workflows/ci.yml

@@ -57,15 +57,14 @@ jobs:
             # contains package information of crates installed via `cargo install`.
             ~/.cargo/.crates.toml
             ~/.cargo/.crates2.json
-          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock', 'cargo-miri/src/version.rs') }}
+          key: ${{ runner.os }}-cargo-${{ hashFiles('**/Cargo.lock') }}
           restore-keys: ${{ runner.os }}-cargo
 
-      - name: Install rustup-toolchain-install-master and xargo
+      - name: Install rustup-toolchain-install-master
         if: ${{ steps.cache.outputs.cache-hit == 'false' }}
         shell: bash
         run: |
           cargo install -f rustup-toolchain-install-master
-          cargo install -f xargo
 
       - name: Install "master" toolchain
         shell: bash

CONTRIBUTING.md

@@ -38,7 +38,7 @@ for you. If you don't want all of these to happen, you can add individual `.auto
 ## Building and testing Miri
 
 Invoking Miri requires getting a bunch of flags right and setting up a custom
-sysroot with xargo. The `miri` script takes care of that for you. With the
+sysroot. The `miri` script takes care of that for you. With the
 build environment prepared, compiling Miri is just one command away:
 
 ```

README.md

@@ -450,7 +450,7 @@ binaries, and as such worth documenting:
   some compiler flags to prepare the code for interpretation; with `host`, this is not done.
   This environment variable is useful to be sure that the compiled `rlib`s are compatible
   with Miri.
-* `MIRI_CALLED_FROM_XARGO` is set during the Miri-induced `xargo` sysroot build,
+* `MIRI_CALLED_FROM_SETUP` is set during the Miri sysroot build,
   which will re-invoke `cargo-miri` as the `rustc` to use for this build.
 * `MIRI_CALLED_FROM_RUSTDOC` when set to any value tells `cargo-miri` that it is
   running as a child process of `rustdoc`, which invokes it twice for each doc-test

cargo-miri/Cargo.toml

@@ -18,6 +18,7 @@ directories = "3"
 rustc_version = "0.4"
 serde_json = "1.0.40"
 cargo_metadata = "0.15.0"
+rustc-build-sysroot = "0.2.1"
 
 # A noop dependency that changes in the Rust repository, it's a bit of a hack.
 # See the `src/tools/rustc-workspace-hack/README.md` file in `rust-lang/rust`

cargo-miri/src/main.rs

@@ -7,7 +7,6 @@ mod util;
 mod arg;
 mod phases;
 mod setup;
-mod version;
 
 use std::{env, iter};
 
@@ -23,8 +22,8 @@ fn main() {
     // Dispatch to `cargo-miri` phase. Here is a rough idea of "who calls who".
     //
     // Initially, we are invoked as `cargo-miri miri run/test`. We first run the setup phase:
-    // - We call `xargo`, and set `RUSTC` back to us, together with `MIRI_CALLED_FROM_XARGO`,
-    //   so that xargo's rustc invocations end up in `phase_rustc` with `RustcPhase::Setup`.
+    // - We use `rustc-build-sysroot`, and set `RUSTC` back to us, together with `MIRI_CALLED_FROM_SETUP`,
+    //   so that the sysroot build rustc invocations end up in `phase_rustc` with `RustcPhase::Setup`.
     //   There we then call the Miri driver with `MIRI_BE_RUSTC` to perform the actual build.
     //
     // Then we call `cargo run/test`, exactly forwarding all user flags, plus some configuration so
@@ -53,7 +52,7 @@ fn main() {
     //     the Miri driver for interpretation.
 
     // Dispatch running as part of sysroot compilation.
-    if env::var_os("MIRI_CALLED_FROM_XARGO").is_some() {
+    if env::var_os("MIRI_CALLED_FROM_SETUP").is_some() {
         phase_rustc(args, RustcPhase::Setup);
         return;
     }

cargo-miri/src/phases.rs

@@ -7,6 +7,8 @@ use std::io::BufReader;
 use std::path::PathBuf;
 use std::process::Command;
 
+use rustc_version::VersionMeta;
+
 use crate::{setup::*, util::*};
 
 const CARGO_MIRI_HELP: &str = r#"Runs binary crates and tests in Miri
@@ -90,12 +92,14 @@ pub fn phase_cargo_miri(mut args: impl Iterator<Item = String>) {
     let verbose = num_arg_flag("-v");
 
     // Determine the involved architectures.
-    let host = version_info().host;
+    let rustc_version = VersionMeta::for_command(miri_for_host())
+        .expect("failed to determine underlying rustc version of Miri");
+    let host = &rustc_version.host;
     let target = get_arg_flag_value("--target");
-    let target = target.as_ref().unwrap_or(&host);
+    let target = target.as_ref().unwrap_or(host);
 
     // We always setup.
-    setup(&subcommand, &host, target);
+    setup(&subcommand, target, &rustc_version);
 
     // Invoke actual cargo for the job, but with different flags.
     // We re-use `cargo test` and `cargo run`, which makes target and binary handling very easy but
@@ -146,7 +150,7 @@ pub fn phase_cargo_miri(mut args: impl Iterator<Item = String>) {
     if get_arg_flag_value("--target").is_none() {
         // No target given. Explicitly pick the host.
         cmd.arg("--target");
-        cmd.arg(&host);
+        cmd.arg(host);
     }
 
     // Set ourselves as runner for al binaries invoked by cargo.
@@ -204,7 +208,7 @@ pub fn phase_cargo_miri(mut args: impl Iterator<Item = String>) {
 
 #[derive(Debug, Copy, Clone, PartialEq)]
 pub enum RustcPhase {
-    /// `rustc` called via `xargo` for sysroot build.
+    /// `rustc` called during sysroot build.
     Setup,
     /// `rustc` called by `cargo` for regular build.
     Build,
@@ -264,7 +268,7 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
     let verbose = std::env::var("MIRI_VERBOSE")
         .map_or(0, |verbose| verbose.parse().expect("verbosity flag must be an integer"));
     let target_crate = is_target_crate();
-    // Determine whether this is cargo/xargo invoking rustc to get some infos.
+    // Determine whether this is cargo invoking rustc to get some infos.
     let info_query = get_arg_flag_value("--print").is_some() || has_arg_flag("-vV");
 
     let store_json = |info: CrateRunInfo| {