Rollup merge of #136542 - jieyouxu:build-base, r=onur-ozkan

[`compiletest`-related cleanups 4/7] Make the distinction between root build directory vs test suite specific build directory in compiletest less confusing

Reference for overall changes: https://github.com/rust-lang/rust/pull/136437
Part **4** of **7** of the *`compiletest`-related cleanups* PR series.

### Summary

- Remove `--build-base` compiletest flag, and introduce `--build-{root,test-suite-root}` flags instead. `--build-base` previously actually is test suite specific build directory, not the root `build/` directory.
- Feed the root build directory directly from bootstrap to compiletest via `--build-root` instead of doing multiple layers of parent unwrapping[^parent] based on the test suite specific build directory.
- Remove a redundant `to_path_buf()`.

[^parent]: Please do not unwrap the parents.

r? bootstrap

1 files changed, 6 insertions, 2 deletions

diff --git a/src/bootstrap/src/core/build_steps/test.rs b/src/bootstrap/src/core/build_steps/test.rs
index dfcf26cedd6..709711d9d34 100644
--- a/src/bootstrap/src/core/build_steps/test.rs
+++ b/src/bootstrap/src/core/build_steps/test.rs
@@ -1793,14 +1793,18 @@ NOTE: if you're sure you want to do this, please open an issue as to why. In the
         cmd.arg("--src-root").arg(&builder.src);
         cmd.arg("--src-test-suite-root").arg(builder.src.join("tests").join(suite));
 
-        cmd.arg("--build-base").arg(testdir(builder, compiler.host).join(suite));
+        // N.B. it's important to distinguish between the *root* build directory, the *host* build
+        // directory immediately under the root build directory, and the test-suite-specific build
+        // directory.
+        cmd.arg("--build-root").arg(&builder.out);
+        cmd.arg("--build-test-suite-root").arg(testdir(builder, compiler.host).join(suite));
 
         // When top stage is 0, that means that we're testing an externally provided compiler.
         // In that case we need to use its specific sysroot for tests to pass.
         let sysroot = if builder.top_stage == 0 {
             builder.initial_sysroot.clone()
         } else {
-            builder.sysroot(compiler).to_path_buf()
+            builder.sysroot(compiler)
         };
 
         cmd.arg("--sysroot-base").arg(sysroot);