bootstrap: respect build.python on macOS

bootstrap.example.toml

@@ -322,7 +322,9 @@
 # Python interpreter to use for various tasks throughout the build, notably
 # rustdoc tests, the lldb python interpreter, and some dist bits and pieces.
 #
-# Defaults to the Python interpreter used to execute x.py.
+# Defaults to the Python interpreter used to execute x.py, or /usr/bin/python3
+# on macOS. Note that LLDB tests require a Python version compatible with the
+# LLDB plugin to be loaded.
 #build.python = "python"
 
 # The path to (or name of) the resource compiler executable to use on Windows.

src/bootstrap/src/lib.rs

@@ -1525,10 +1525,11 @@ impl Build {
     /// Path to the python interpreter to use
     fn python(&self) -> &Path {
         if self.config.host_target.ends_with("apple-darwin") {
-            // Force /usr/bin/python3 on macOS for LLDB tests because we're loading the
-            // LLDB plugin's compiled module which only works with the system python
-            // (namely not Homebrew-installed python)
-            Path::new("/usr/bin/python3")
+            // LLDB tests require the Python version the LLDB plugin was built for.
+            // On macOS, the system Python/LLDB are compatible. Many users install
+            // Homebrew Python but not Homebrew LLVM, so default to system Python.
+            // Can be overridden via `build.python` for custom LLVM installations.
+            self.config.python.as_deref().unwrap_or_else(|| Path::new("/usr/bin/python3"))
         } else {
             self.config
                 .python

src/bootstrap/src/utils/change_tracker.rs

@@ -576,4 +576,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Info,
         summary: "`llvm.enzyme` now works with `download-ci-llvm=true`.",
     },
+    ChangeInfo {
+        change_id: 148636,
+        severity: ChangeSeverity::Info,
+        summary: "The `build.python` option is now respected on macOS (previously ignored).",
+    },
 ];