Merge #803

803: add `CROSS_CUSTOM_TOOLCHAIN` to disable automatic target component downloading r=Alexhuszagh a=Emilgardis

This adds an environment variable `CROSS_CUSTOM_TOOLCHAIN` to disable some rustup commands.

The way to use this with `cargo-bisect-rustc` is `cargo bisect-rustc --script=./bisect.sh --target powerpc64le-unknown-linux-gnu` and the script is

```sh
#!/usr/bin/env bash

export CROSS_CUSTOM_TOOLCHAIN=1
exec cross run --target powerpc64le-unknown-linux-gnu
```

I've filed rust-lang/cargo-bisect-rustc#159 to avoid the pitfall that was discovered when not specifying `--target`

resolves #699


Co-authored-by: Emil Gardström <emil.gardstrom@gmail.com>

CHANGELOG.md

@@ -7,6 +7,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- #803 - added `CROSS_CUSTOM_TOOLCHAIN` to disable automatic installation of components for use with tools like `cargo-bisect-rustc`
 - #795 - added images for additional toolchains maintained by cross-rs.
 - #792 - added `CROSS_CONTAINER_IN_CONTAINER` environment variable to replace `CROSS_DOCKER_IN_DOCKER`.
 - #782 - added `build-std` config option, which builds the rust standard library from source if enabled.

src/lib.rs

@@ -416,35 +416,37 @@ pub fn run() -> Result<ExitStatus> {
                 is_nightly = channel == Channel::Nightly;
             }
 
-            // build-std overrides xargo, but only use it if it's a built-in
-            // tool but not an available target or doesn't have rust-std.
-            let available_targets = rustup::available_targets(&toolchain, verbose)?;
             let uses_build_std = config.build_std(&target).unwrap_or(false);
             let uses_xargo =
                 !uses_build_std && config.xargo(&target).unwrap_or(!target.is_builtin());
-            if !is_nightly && uses_build_std {
-                eyre::bail!(
-                    "no rust-std component available for {}: must use nightly",
-                    target.triple()
-                );
-            }
-
-            if !uses_xargo
-                && !available_targets.is_installed(&target)
-                && available_targets.contains(&target)
-            {
-                rustup::install(&target, &toolchain, verbose)?;
-            } else if !rustup::component_is_installed("rust-src", &toolchain, verbose)? {
-                rustup::install_component("rust-src", &toolchain, verbose)?;
-            }
+            if std::env::var("CROSS_CUSTOM_TOOLCHAIN").is_err() {
+                // build-std overrides xargo, but only use it if it's a built-in
+                // tool but not an available target or doesn't have rust-std.
+                let available_targets = rustup::available_targets(&toolchain, verbose)?;
+
+                if !is_nightly && uses_build_std {
+                    eyre::bail!(
+                        "no rust-std component available for {}: must use nightly",
+                        target.triple()
+                    );
+                }
 
-            if args
-                .subcommand
-                .map(|sc| sc == Subcommand::Clippy)
-                .unwrap_or(false)
-                && !rustup::component_is_installed("clippy", &toolchain, verbose)?
-            {
-                rustup::install_component("clippy", &toolchain, verbose)?;
+                if !uses_xargo
+                    && !available_targets.is_installed(&target)
+                    && available_targets.contains(&target)
+                {
+                    rustup::install(&target, &toolchain, verbose)?;
+                } else if !rustup::component_is_installed("rust-src", &toolchain, verbose)? {
+                    rustup::install_component("rust-src", &toolchain, verbose)?;
+                }
+                if args
+                    .subcommand
+                    .map(|sc| sc == Subcommand::Clippy)
+                    .unwrap_or(false)
+                    && !rustup::component_is_installed("clippy", &toolchain, verbose)?
+                {
+                    rustup::install_component("clippy", &toolchain, verbose)?;
+                }
             }
 
             let needs_interpreter = args

src/rustup.rs

@@ -4,7 +4,7 @@ use std::process::Command;
 use rustc_version::{Channel, Version};
 
 use crate::errors::*;
-use crate::extensions::CommandExt;
+pub use crate::extensions::{CommandExt, OutputExt};
 use crate::Target;
 
 #[derive(Debug)]
@@ -43,10 +43,17 @@ pub fn installed_toolchains(verbose: bool) -> Result<Vec<String>> {
 }
 
 pub fn available_targets(toolchain: &str, verbose: bool) -> Result<AvailableTargets> {
-    let out = Command::new("rustup")
-        .args(&["target", "list", "--toolchain", toolchain])
-        .run_and_get_stdout(verbose)?;
+    let mut cmd = Command::new("rustup");
+    cmd.args(&["target", "list", "--toolchain", toolchain]);
+    let output = cmd.run_and_get_output(verbose)?;
 
+    if !output.status.success() {
+        if String::from_utf8_lossy(&output.stderr).contains("is a custom toolchain") {
+            eyre::bail!("{toolchain} is a custom toolchain. To use it, you'll need to set the environment variable `CROSS_CUSTOM_TOOLCHAIN=1`")
+        }
+        return Err(cmd.status_result(output.status).unwrap_err().into());
+    }
+    let out = output.stdout()?;
     let mut default = String::new();
     let mut installed = vec![];
     let mut not_installed = vec![];