feat(e2e): Source-built Python interpreter with uv deps

e2e/MODULE.bazel

@@ -159,3 +159,8 @@ uv.project(
 # }}}
 
 use_repo(uv, "pypi")
+
+# For cases/source-built-python
+# {{{
+include("//cases/source-built-python:source-built-python.MODULE.bazel")
+# }}}

e2e/cases/source-built-python/BUILD.bazel

@@ -0,0 +1,94 @@
+load("@aspect_rules_py//py/unstable:defs.bzl", "py_venv_test")
+load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
+load("@rules_python//python:defs.bzl", "py_runtime", "py_runtime_pair")
+load(":defs.bzl", "build_cpython", "python_interpreter_wrapper", "source_built_test")
+
+# -- Build CPython 3.11.9 from source --
+
+build_cpython(
+    name = "cpython",
+    src = "@cpython_src//:all_srcs",
+)
+
+# Wrapper script that sets PYTHONHOME before exec-ing the real interpreter
+python_interpreter_wrapper(
+    name = "python3",
+    cpython = ":cpython",
+)
+
+# -- Toolchain registration --
+
+py_runtime(
+    name = "source_built_runtime",
+    files = [":cpython"],
+    interpreter = ":python3",
+    interpreter_version_info = {
+        "major": "3",
+        "minor": "11",
+        "micro": "9",
+    },
+    python_version = "PY3",
+)
+
+py_runtime_pair(
+    name = "source_built_py_runtime_pair",
+    py3_runtime = ":source_built_runtime",
+)
+
+# Gate the toolchain behind a build setting so it doesn't affect other tests
+string_flag(
+    name = "python_build_type",
+    build_setting_default = "prebuilt",
+    values = [
+        "prebuilt",
+        "source",
+    ],
+)
+
+config_setting(
+    name = "is_source_built",
+    flag_values = {":python_build_type": "source"},
+)
+
+toolchain(
+    name = "source_built_toolchain",
+    target_settings = [":is_source_built"],
+    toolchain = ":source_built_py_runtime_pair",
+    toolchain_type = "@rules_python//python:toolchain_type",
+)
+
+# -- Tests --
+
+# Inner test (built under the source-built Python toolchain via transition)
+py_venv_test(
+    name = "_test_source_built_inner",
+    srcs = ["test_source_built.py"],
+    main = "test_source_built.py",
+    python_version = "3.11",
+    tags = ["manual"],
+)
+
+# Outer test that transitions to activate the source-built toolchain
+source_built_test(
+    name = "test_source_built",
+    test = ":_test_source_built_inner",
+)
+
+# Inner test with sdist-built markupsafe (forced via no-binary-package in pyproject.toml)
+py_venv_test(
+    name = "_test_with_deps_inner",
+    srcs = ["test_with_deps.py"],
+    main = "test_with_deps.py",
+    python_version = "3.11",
+    tags = ["manual"],
+    venv = "test",
+    deps = [
+        "@pypi//markupsafe",
+    ],
+)
+
+# Outer test with deps, transitioned to use source-built debug Python
+source_built_test(
+    name = "test_with_deps",
+    test = ":_test_with_deps_inner",
+)

e2e/cases/source-built-python/cpython_src.BUILD.bazel

@@ -0,0 +1,5 @@
+filegroup(
+    name = "all_srcs",
+    srcs = glob(["**"]),
+    visibility = ["//visibility:public"],
+)

e2e/cases/source-built-python/defs.bzl

@@ -0,0 +1,157 @@
+"""Helpers for the source-built Python e2e test."""
+
+# -- Build CPython from source as a Bazel action --
+
+def _build_cpython_impl(ctx):
+    """Builds CPython from source using ./configure && make && make install."""
+    install_dir = ctx.actions.declare_directory(ctx.attr.name)
+
+    src_files = ctx.attr.src[DefaultInfo].files
+
+    # Find the configure script — pick the one with the shortest path
+    # (the top-level one, vs. subdirectory configure scripts).
+    configure = None
+    for f in src_files.to_list():
+        if f.basename == "configure":
+            if configure == None or len(f.path) < len(configure.path):
+                configure = f
+
+    if not configure:
+        fail("Could not find 'configure' script in source files")
+
+    ctx.actions.run_shell(
+        inputs = src_files,
+        outputs = [install_dir],
+        command = """\
+set -euo pipefail
+SRC_DIR="$(cd "$(dirname "{configure}")" && pwd)"
+INSTALL_DIR="$(pwd)/{install_dir}"
+
+cd "$SRC_DIR"
+./configure \
+    --prefix="$INSTALL_DIR" \
+    --without-ensurepip \
+    --disable-test-modules \
+    --with-pydebug \
+    2>&1
+
+make -j"$(nproc)" 2>&1
+make install 2>&1
+""".format(
+            configure = configure.path,
+            install_dir = install_dir.path,
+        ),
+        mnemonic = "BuildCPython",
+        progress_message = "Building CPython from source",
+        use_default_shell_env = True,
+    )
+
+    return [DefaultInfo(files = depset([install_dir]))]
+
+build_cpython = rule(
+    implementation = _build_cpython_impl,
+    attrs = {
+        "src": attr.label(mandatory = True),
+    },
+)
+
+# -- Wrapper script to set PYTHONHOME --
+
+def _python_interpreter_wrapper_impl(ctx):
+    """Creates a wrapper script that sets PYTHONHOME before exec-ing the real interpreter."""
+    cpython_tree = None
+    for f in ctx.attr.cpython[DefaultInfo].files.to_list():
+        if f.is_directory:
+            cpython_tree = f
+            break
+
+    if not cpython_tree:
+        fail("No directory (tree artifact) found in cpython outputs")
+
+    wrapper = ctx.actions.declare_file(ctx.attr.name)
+    ctx.actions.write(
+        output = wrapper,
+        content = """\
+#!/bin/bash
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+export PYTHONHOME="$SCRIPT_DIR/{tree_basename}"
+exec "$PYTHONHOME/bin/{binary}" "$@"
+""".format(
+            tree_basename = cpython_tree.basename,
+            binary = ctx.attr.binary,
+        ),
+        is_executable = True,
+    )
+
+    return [DefaultInfo(
+        files = depset([wrapper]),
+        runfiles = ctx.runfiles(files = [cpython_tree]),
+    )]
+
+python_interpreter_wrapper = rule(
+    implementation = _python_interpreter_wrapper_impl,
+    attrs = {
+        "cpython": attr.label(mandatory = True),
+        "binary": attr.string(default = "python3.11"),
+    },
+)
+
+# -- Transition to activate the source-built Python toolchain --
+
+def _source_built_transition_impl(settings, attr):
+    return {"//cases/source-built-python:python_build_type": "source"}
+
+_source_built_transition = transition(
+    implementation = _source_built_transition_impl,
+    inputs = [],
+    outputs = ["//cases/source-built-python:python_build_type"],
+)
+
+def _source_built_test_impl(ctx):
+    inner = ctx.attr.test[0]
+    inner_di = inner[DefaultInfo]
+
+    inner_executable = inner_di.files_to_run.executable
+
+    executable = ctx.actions.declare_file(ctx.attr.name + ".sh")
+    ctx.actions.write(
+        output = executable,
+        content = """\
+#!/bin/bash
+# Resolve RUNFILES_DIR from the Bazel test environment
+if [[ -z "$RUNFILES_DIR" ]]; then
+    if [[ -d "$TEST_SRCDIR" ]]; then
+        RUNFILES_DIR="$TEST_SRCDIR"
+    elif [[ -d "$0.runfiles" ]]; then
+        RUNFILES_DIR="$0.runfiles"
+    fi
+fi
+exec "$RUNFILES_DIR/{workspace}/{inner}" "$@"
+""".format(
+            workspace = ctx.workspace_name,
+            inner = inner_executable.short_path,
+        ),
+        is_executable = True,
+    )
+
+    runfiles = ctx.runfiles(files = [inner_executable])
+    runfiles = runfiles.merge(inner_di.default_runfiles)
+
+    return [DefaultInfo(
+        executable = executable,
+        runfiles = runfiles,
+    )]
+
+source_built_test = rule(
+    implementation = _source_built_test_impl,
+    test = True,
+    attrs = {
+        "test": attr.label(
+            mandatory = True,
+            cfg = _source_built_transition,
+        ),
+        "_allowlist_function_transition": attr.label(
+            default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+        ),
+    },
+)

e2e/cases/source-built-python/pyproject.toml

@@ -0,0 +1,15 @@
+[project]
+name = "source-built-python-test"
+version = "0.1.0"
+requires-python = ">=3.11"
+dependencies = []
+
+[dependency-groups]
+test = [
+    "markupsafe>=2.1",
+    "build",
+    "setuptools",
+]
+
+[tool.uv]
+no-binary-package = ["markupsafe"]

e2e/cases/source-built-python/source-built-python.MODULE.bazel

@@ -0,0 +1,20 @@
+"Source-built Python interpreter e2e test"
+
+http_archive = use_repo_rule("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+http_archive(
+    name = "cpython_src",
+    build_file = "//cases/source-built-python:cpython_src.BUILD.bazel",
+    sha256 = "e7de3240a8bc2b1e1ba5c81bf943f06861ff494b69fda990ce2722a504c6153d",
+    strip_prefix = "Python-3.11.9",
+    url = "https://www.python.org/ftp/python/3.11.9/Python-3.11.9.tgz",
+)
+
+register_toolchains("//cases/source-built-python:source_built_toolchain")
+
+uv = use_extension("@aspect_rules_py//uv/unstable:extension.bzl", "uv")
+uv.project(
+    hub_name = "pypi",
+    lock = "//cases/source-built-python:uv.lock",
+    pyproject = "//cases/source-built-python:pyproject.toml",
+)

e2e/cases/source-built-python/test_source_built.py

@@ -0,0 +1,54 @@
+"""Verify that the Python interpreter was built from source."""
+
+import sys
+import sysconfig
+
+
+def test_version():
+    """Check we're running on CPython 3.11.9."""
+    assert sys.version_info[:3] == (3, 11, 9), (
+        f"Expected CPython 3.11.9, got {sys.version}"
+    )
+
+
+def test_source_built_prefix():
+    """Check that the interpreter was built with a non-standard prefix.
+
+    Source-built interpreters have sysconfig CONFIG_ARGS reflecting the
+    configure invocation, and sys.prefix pointing to the build install tree
+    rather than a standard system path like /usr or /usr/local.
+    """
+    config_args = sysconfig.get_config_var("CONFIG_ARGS") or ""
+    # The configure_make rule uses --prefix during the build
+    assert "--prefix" in config_args, (
+        f"Expected --prefix in CONFIG_ARGS, got: {config_args}"
+    )
+
+    # The prefix should NOT be a standard system path
+    prefix = sys.prefix
+    assert prefix not in ("/usr", "/usr/local", "/opt/homebrew"), (
+        f"Expected non-system prefix, got: {prefix}"
+    )
+
+
+def test_debug_build():
+    """Verify this is a debug build (--with-pydebug).
+
+    Debug builds set sys.abiflags = 'd' and SOABI contains 'cpython-311d'.
+    PBS never ships debug builds, so this definitively proves source-built.
+    """
+    assert hasattr(sys, "abiflags"), "sys.abiflags not found"
+    assert "d" in sys.abiflags, (
+        f"Expected 'd' in abiflags (debug build), got: {sys.abiflags!r}"
+    )
+    soabi = sysconfig.get_config_var("SOABI") or ""
+    assert "cpython-311d" in soabi, (
+        f"Expected 'cpython-311d' in SOABI, got: {soabi!r}"
+    )
+
+
+if __name__ == "__main__":
+    test_version()
+    test_source_built_prefix()
+    test_debug_build()
+    print("All checks passed: running on source-built debug CPython 3.11.9")