Add temporary directory for executing snapshot tests

src/bootstrap/src/core/builder/tests.rs

@@ -1242,12 +1242,13 @@ mod staging {
     use crate::core::builder::tests::{
         TEST_TRIPLE_1, configure, configure_with_args, render_steps, run_build,
     };
-    use crate::utils::tests::ConfigBuilder;
+    use crate::utils::tests::{ConfigBuilder, TestCtx};
 
     #[test]
     fn build_compiler_stage_1() {
+        let ctx = TestCtx::new();
         insta::assert_snapshot!(
-            ConfigBuilder::build()
+            ctx.config("build")
                 .path("compiler")
                 .stage(1)
                 .get_steps(), @r"

src/bootstrap/src/utils/tests/mod.rs

@@ -1,25 +1,49 @@
 //! This module contains shared utilities for bootstrap tests.
 
+use std::path::{Path, PathBuf};
+use std::thread;
+
+use tempfile::TempDir;
+
 use crate::core::builder::Builder;
 use crate::core::config::DryRun;
-use crate::{Build, Config, Flags};
+use crate::{Build, Config, Flags, t};
 
 pub mod git;
 
+/// Holds temporary state of a bootstrap test.
+/// Right now it is only used to redirect the build directory of the bootstrap
+/// invocation, in the future it would be great if we could actually execute
+/// the whole test with this directory set as the workdir.
+pub struct TestCtx {
+    directory: TempDir,
+}
+
+impl TestCtx {
+    pub fn new() -> Self {
+        let directory = TempDir::new().expect("cannot create temporary directory");
+        eprintln!("Running test in {}", directory.path().display());
+        Self { directory }
+    }
+
+    /// Starts a new invocation of bootstrap that executes `kind` as its top level command
+    /// (i.e. `x <kind>`). Returns a builder that configures the created config through CLI flags.
+    pub fn config(&self, kind: &str) -> ConfigBuilder {
+        ConfigBuilder::from_args(&[kind], self.directory.path().to_owned())
+    }
+}
+
 /// Used to configure an invocation of bootstrap.
 /// Currently runs in the rustc checkout, long-term it should be switched
 /// to run in a (cache-primed) temporary directory instead.
 pub struct ConfigBuilder {
     args: Vec<String>,
+    directory: PathBuf,
 }
 
 impl ConfigBuilder {
-    pub fn from_args(args: &[&str]) -> Self {
-        Self::new(args)
-    }
-
-    pub fn build() -> Self {
-        Self::new(&["build"])
+    fn from_args(args: &[&str], directory: PathBuf) -> Self {
+        Self { args: args.iter().copied().map(String::from).collect(), directory }
     }
 
     pub fn path(mut self, path: &str) -> Self {
@@ -33,14 +57,18 @@ impl ConfigBuilder {
         self
     }
 
-    fn new(args: &[&str]) -> Self {
-        Self { args: args.iter().copied().map(String::from).collect() }
-    }
-
     pub fn create_config(mut self) -> Config {
-        let mut config = Config::parse(Flags::parse(&self.args));
         // Run in dry-check, otherwise the test would be too slow
-        config.set_dry_run(DryRun::SelfCheck);
-        config
+        self.args.push("--dry-run".to_string());
+
+        // Ignore submodules
+        self.args.push("--set".to_string());
+        self.args.push("build.submodules=false".to_string());
+
+        // Do not mess with the local rustc checkout build directory
+        self.args.push("--build-dir".to_string());
+        self.args.push(self.directory.join("build").display().to_string());
+
+        Config::parse(Flags::parse(&self.args))
     }
 }