Remove support for different src directory

This requires that bootstrap is run from the same worktree as the sources it'll
build, but this is basically required for the build to work anyway. You can
still run it from a different directory, just that the files it builds must be
beside it.

src/bootstrap/bootstrap.py

@@ -966,7 +966,6 @@ def bootstrap(help_triggered):
     parser = argparse.ArgumentParser(description='Build rust')
     parser.add_argument('--config')
     parser.add_argument('--build')
-    parser.add_argument('--src')
     parser.add_argument('--clean', action='store_true')
     parser.add_argument('-v', '--verbose', action='count', default=0)
 
@@ -975,7 +974,7 @@ def bootstrap(help_triggered):
 
     # Configure initial bootstrap
     build = RustBuild()
-    build.rust_root = args.src or os.path.abspath(os.path.join(__file__, '../../..'))
+    build.rust_root = os.path.abspath(os.path.join(__file__, '../../..'))
     build.verbose = args.verbose
     build.clean = args.clean
 
@@ -1032,7 +1031,6 @@ def bootstrap(help_triggered):
     args = [build.bootstrap_binary()]
     args.extend(sys.argv[1:])
     env = os.environ.copy()
-    env["SRC"] = build.rust_root
     env["BOOTSTRAP_PARENT_ID"] = str(os.getpid())
     env["BOOTSTRAP_PYTHON"] = sys.executable
     env["BUILD_DIR"] = build.build_dir

src/bootstrap/config.rs

@@ -488,7 +488,9 @@ impl Config {
 
         // set by bootstrap.py
         config.build = TargetSelection::from_user(&env!("BUILD_TRIPLE"));
-        config.src = Config::path_from_python("SRC");
+        let manifest_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+        // Undo `src/bootstrap`
+        config.src = manifest_dir.parent().unwrap().parent().unwrap().to_owned();
         config.out = Config::path_from_python("BUILD_DIR");
 
         config.initial_rustc = Config::path_from_python("RUSTC");