fix(bootstrap): restore imports for native Python targets

news/native-bootstrap-imports.fixed.md

@@ -0,0 +1,4 @@
+(bootstrap) Bazel 7 native Python targets can run with both the Python and
+shell bootstraps without crashing on unexpanded launcher placeholders. Their
+declared import roots and repository imports are available when the launcher
+falls back to executing the main file directly.

python/private/python_bootstrap_template.txt

@@ -39,6 +39,7 @@ import subprocess
 _STAGE2_BOOTSTRAP_SENTINEL = "%stage2" + "_bootstrap%"
 # runfiles-root-relative path
 STAGE2_BOOTSTRAP="%stage2_bootstrap%"
+_USING_STAGE2_BOOTSTRAP_FALLBACK = False
 
 # NOTE: The fallback logic from stage2_bootstrap to main is only present
 # as a courtesy for an older, unsupported, configuration. It can be removed
@@ -49,6 +50,7 @@ if STAGE2_BOOTSTRAP == _STAGE2_BOOTSTRAP_SENTINEL:
   _main = "%main%"
   if _main != _MAIN_SENTINEL and _main:
     STAGE2_BOOTSTRAP = _main
+    _USING_STAGE2_BOOTSTRAP_FALLBACK = True
   else:
     STAGE2_BOOTSTRAP = ""
 
@@ -98,7 +100,13 @@ else:
 RUNTIME_VENV_SYMLINKS = """
 %runtime_venv_symlinks%
 """.strip().split("\n")
-RUNTIME_VENV_SYMLINKS = dict(line.split("|") for line in RUNTIME_VENV_SYMLINKS if line)
+# Native rules leave this newer placeholder unchanged. They have no runtime
+# venv symlinks; only parse entries when the placeholder was expanded.
+_RUNTIME_VENV_SYMLINKS_SENTINEL = "%runtime_venv" + "_symlinks%"
+if RUNTIME_VENV_SYMLINKS == [_RUNTIME_VENV_SYMLINKS_SENTINEL]:
+  RUNTIME_VENV_SYMLINKS = {}
+else:
+  RUNTIME_VENV_SYMLINKS = dict(line.split("|") for line in RUNTIME_VENV_SYMLINKS if line)
 
 ADDITIONAL_INTERPRETER_ARGS = os.environ.get("RULES_PYTHON_ADDITIONAL_INTERPRETER_ARGS", "")
 EXTRACT_ROOT = os.environ.get("RULES_PYTHON_EXTRACT_ROOT")
@@ -614,6 +622,29 @@ def main():
 
   print_verbose("runfiles root:", runfiles_root)
 
+  if _USING_STAGE2_BOOTSTRAP_FALLBACK:
+    # Native rules expand %imports% and %import_all%, but do not generate
+    # stage 2 to set up sys.path. Preserve the native launcher's import order
+    # when executing the main file directly; leave regular stage-2 launches
+    # unchanged. These paths are runfiles-relative, not checkout-relative.
+    imports = "%imports%"
+    python_paths = [runfiles_root]
+    python_paths.extend(join(runfiles_root, path) for path in imports.split(":") if path)
+    if "%import_all%" == "True":
+      python_paths.extend(
+          join(runfiles_root, repo) for repo in sorted(os.listdir(runfiles_root))
+          if os.path.isdir(join(runfiles_root, repo)))
+    else:
+      python_paths.append(join(runfiles_root, WORKSPACE_NAME))
+    python_paths = [get_windows_path_with_unc_prefix(path) for path in python_paths]
+    existing_pythonpath = os.environ.get("PYTHONPATH")
+    if existing_pythonpath:
+      python_paths.extend(existing_pythonpath.split(os.pathsep))
+    new_env["PYTHONPATH"] = os.pathsep.join(dict.fromkeys(python_paths))
+    if IS_WINDOWS:
+      new_env["PYTHONPATH"] = new_env["PYTHONPATH"].replace("/", os.sep)
+    print_verbose("native fallback PYTHONPATH:", new_env["PYTHONPATH"])
+
   if os.environ.get("RULES_PYTHON_TESTING_TELL_RUNFILES_ROOT"):
     new_env["RULES_PYTHON_TESTING_RUNFILES_ROOT"] = runfiles_root
 

python/private/stage1_bootstrap_template.sh

@@ -33,6 +33,24 @@ function _symlink() {
 # runfiles-root-relative path
 STAGE2_BOOTSTRAP="%stage2_bootstrap%"
 
+# Like the Python bootstrap, fall back to the main file for native rules,
+# which expand %main% but leave newer stage-2 placeholders unchanged.
+_STAGE2_BOOTSTRAP_SENTINEL="%stage2""_bootstrap%"
+_INTERPRETER_ARGS_SENTINEL="%interpreter""_args%"
+USING_STAGE2_BOOTSTRAP_FALLBACK=0
+if [[ "$STAGE2_BOOTSTRAP" == "$_STAGE2_BOOTSTRAP_SENTINEL" ]]; then
+  _MAIN_SENTINEL="%main""%"
+  main="%main%"
+  if [[ "$main" == "$_MAIN_SENTINEL" || -z "$main" ]]; then
+    echo >&2 "ERROR: %stage2_bootstrap% (or %main%) was not substituted."
+    exit 1
+  fi
+  # Native external targets use workspace/../repo/main.py. The workspace
+  # directory need not exist, so remove that prefix before accessing the file.
+  STAGE2_BOOTSTRAP="${main#"%workspace_name%/../"}"
+  USING_STAGE2_BOOTSTRAP_FALLBACK=1
+fi
+
 # runfiles-root-relative path to python interpreter to use.
 # This is the `bin/python3` path in the binary's venv.
 PYTHON_BINARY='%python_binary%'
@@ -60,6 +78,11 @@ declare -a INTERPRETER_ARGS_FROM_TARGET=(
 %interpreter_args%
 )
 
+if [[ "$USING_STAGE2_BOOTSTRAP_FALLBACK" == "1" &&
+      "${INTERPRETER_ARGS_FROM_TARGET[*]}" == "$_INTERPRETER_ARGS_SENTINEL" ]]; then
+  INTERPRETER_ARGS_FROM_TARGET=()
+fi
+
 if [[ "$IS_ZIPFILE" == "1" ]]; then
   # NOTE: Macs have an old version of mktemp, so we must use only the
   # minimal functionality of it.
@@ -309,6 +332,33 @@ fi
 
 export RUNFILES_DIR
 
+if [[ "$USING_STAGE2_BOOTSTRAP_FALLBACK" == "1" ]]; then
+  # Restore native import order when there is no stage 2 to set up sys.path.
+  # Declared imports are used as provided, without workspace-specific paths.
+  declare -a python_paths=("$RUNFILES_DIR")
+  imports="%imports%"
+  IFS=: read -r -a import_paths <<< "$imports"
+  for import_path in "${import_paths[@]}"; do
+    python_paths+=("$RUNFILES_DIR/$import_path")
+  done
+
+  if [[ "%import_all%" == "True" ]]; then
+    for repo_root in "$RUNFILES_DIR"/*; do
+      if [[ -d "$repo_root" ]]; then
+        python_paths+=("$repo_root")
+      fi
+    done
+  else
+    python_paths+=("$RUNFILES_DIR/%workspace_name%")
+  fi
+
+  python_path="$(IFS=:; echo "${python_paths[*]}")"
+  if [[ -n "${PYTHONPATH:-}" ]]; then
+    python_path+=":$PYTHONPATH"
+  fi
+  interpreter_env+=("PYTHONPATH=$python_path")
+fi
+
 if command -v env >/dev/null 2>&1; then
   ENV_CMD="env"
 else

tests/bootstrap_impls/BUILD.bazel

@@ -20,6 +20,23 @@ load("//tests/support:support.bzl", "SUPPORTS_BOOTSTRAP_SCRIPT")
 load("//tests/support/pytest_test:pytest_test.bzl", "pytest_test")
 load(":venv_relative_path_tests.bzl", "relative_path_test_suite")
 
+py_test(
+    name = "native_bootstrap_test",
+    srcs = ["native_bootstrap_test.py"],
+    data = ["//python/private:python_bootstrap_template.txt"],
+    deps = ["//python/runfiles"],
+)
+
+py_test(
+    name = "native_bootstrap_script_test",
+    srcs = ["native_bootstrap_test.py"],
+    data = ["//python/private:stage1_bootstrap_template"],
+    env = {"BOOTSTRAP": "script"},
+    main = "native_bootstrap_test.py",
+    target_compatible_with = SUPPORTS_BOOTSTRAP_SCRIPT,
+    deps = ["//python/runfiles"],
+)
+
 py_reconfig_binary(
     name = "bootstrap_script_zipapp_bin",
     srcs = ["bin.py"],