Add RustcCli

... which stream lines the call to the `rustc` binary.

`RustcCli` will be used to decide the host and target libdir in a following commit.

Author: 06393993

Cargo.lock

@@ -41,6 +41,9 @@ swrite.workspace = true
 thiserror = "1.0.60"
 nextest-workspace-hack.workspace = true
 
+[dev-dependencies]
+camino-tempfile = "1.1.1"
+
 [features]
 default = ["default-no-update", "self-update"]
 experimental-tokio-console = ["nextest-runner/experimental-tokio-console"]

cargo-nextest/Cargo.toml

@@ -31,6 +31,7 @@ cfg-if = "1.0.0"
 chrono = "0.4.38"
 debug-ignore.workspace = true
 display-error-chain = "0.2.0"
+duct = "0.13.7"
 either = "1.11.0"
 futures = "0.3.30"
 guppy = "0.17.5"
@@ -130,7 +131,6 @@ self_update = { version = "0.39.0", optional = true }
 
 [dev-dependencies]
 color-eyre = { version = "0.6.3", default-features = false }
-duct = "0.13.7"
 indoc = "2.0.5"
 insta = { version = "1.39.0", default-features = false }
 maplit = "1.0.2"

nextest-runner/Cargo.toml

@@ -24,6 +24,10 @@ pub mod redact;
 pub mod reporter;
 pub mod reuse_build;
 pub mod runner;
+// TODO: move this module to the cargo-nextest crate and make it a private module once we get rid of
+// the tests in nextest-runner/tests/integration which depend on this to provide correct host and
+// target libdir.
+mod rustc_cli;
 pub mod show_config;
 pub mod signal;
 pub mod target_runner;
@@ -34,3 +38,5 @@ mod time;
 #[cfg(feature = "self-update")]
 pub mod update;
 pub mod write_str;
+
+pub use rustc_cli::RustcCli;

nextest-runner/src/lib.rs

@@ -0,0 +1,145 @@
+// Copyright (c) The nextest Contributors
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+use crate::cargo_config::TargetTriple;
+use camino::Utf8PathBuf;
+use std::{borrow::Cow, path::PathBuf};
+
+/// Create a rustc CLI call.
+#[derive(Clone, Debug)]
+pub struct RustcCli<'a> {
+    rustc_path: Utf8PathBuf,
+    args: Vec<Cow<'a, str>>,
+}
+
+impl<'a> RustcCli<'a> {
+    /// Create a rustc CLI call: `rustc --print target-libdir`.
+    pub fn print_host_libdir() -> Self {
+        let mut cli = Self::default();
+        cli.add_arg("--print").add_arg("target-libdir");
+        cli
+    }
+
+    /// Create a rustc CLI call: `rustc --print target-libdir --target <triple>`.
+    pub fn print_target_libdir(triple: &'a TargetTriple) -> Self {
+        let mut cli = Self::default();
+        cli.add_arg("--print")
+            .add_arg("target-libdir")
+            .add_arg("--target")
+            .add_arg(triple.platform.triple_str());
+        cli
+    }
+
+    fn add_arg(&mut self, arg: impl Into<Cow<'a, str>>) -> &mut Self {
+        self.args.push(arg.into());
+        self
+    }
+
+    fn to_expression(&self) -> duct::Expression {
+        duct::cmd(
+            self.rustc_path.as_str(),
+            self.args.iter().map(|arg| arg.as_ref()),
+        )
+    }
+
+    /// Execute the command, capture its standard output, and return the captured output as a
+    /// [`Vec<u8>`].
+    pub fn read(&self) -> Option<Vec<u8>> {
+        let expression = self.to_expression();
+        log::trace!("Executing command: {:?}", expression);
+        let output = match expression
+            .stdout_capture()
+            .stderr_capture()
+            .unchecked()
+            .run()
+        {
+            Ok(output) => output,
+            Err(e) => {
+                log::debug!("Failed to spawn the child process: {}", e);
+                return None;
+            }
+        };
+        if !output.status.success() {
+            log::debug!("The execution of the command failed with {}", output.status);
+            log::debug!("stdout:");
+            log::debug!("{}", String::from_utf8_lossy(&output.stdout));
+            log::debug!("stderr:");
+            log::debug!("{}", String::from_utf8_lossy(&output.stderr));
+            return None;
+        }
+        Some(output.stdout)
+    }
+}
+
+impl<'a> Default for RustcCli<'a> {
+    fn default() -> Self {
+        Self {
+            rustc_path: rustc_path(),
+            args: vec![],
+        }
+    }
+}
+
+fn rustc_path() -> Utf8PathBuf {
+    match std::env::var_os("RUSTC") {
+        Some(rustc_path) => PathBuf::from(rustc_path)
+            .try_into()
+            .expect("RUSTC env var is not valid UTF-8"),
+        None => Utf8PathBuf::from("rustc"),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use camino_tempfile::Utf8TempDir;
+    use std::env;
+
+    #[test]
+    fn test_should_run_rustc_version() {
+        let mut cli = RustcCli::default();
+        cli.add_arg("--version");
+        let output = cli.read().expect("rustc --version should run successfully");
+        let output = String::from_utf8(output).expect("the output should be valid utf-8");
+        assert!(
+            output.starts_with("rustc"),
+            "The output should start with rustc, but the actual output is: {}",
+            output
+        );
+    }
+
+    #[test]
+    fn test_should_respect_rustc_env() {
+        env::set_var("RUSTC", "cargo");
+        let mut cli = RustcCli::default();
+        cli.add_arg("--version");
+        let output = cli.read().expect("cargo --version should run successfully");
+        let output = String::from_utf8(output).expect("the output should be valid utf-8");
+        assert!(
+            output.starts_with("cargo"),
+            "The output should start with cargo, but the actual output is: {}",
+            output
+        );
+    }
+
+    #[test]
+    fn test_fail_to_spawn() {
+        let fake_dir = Utf8TempDir::new().expect("should create the temp dir successfully");
+        // No OS will allow executing a directory.
+        env::set_var("RUSTC", fake_dir.path());
+        let mut cli = RustcCli::default();
+        cli.add_arg("--version");
+        let output = cli.read();
+        assert_eq!(output, None);
+    }
+
+    #[test]
+    fn test_execute_with_failure() {
+        let mut cli = RustcCli::default();
+        // rustc --print Y7uDG1HrrY should fail
+        cli.add_arg("--print");
+        cli.add_arg("Y7uDG1HrrY");
+        let output = cli.read();
+        assert_eq!(output, None);
+    }
+}