fix: Add libs/python3.lib to libpython target for SABI builds on Windows (bazel-contrib#1820)

nicholasjng · rickeylev · web-flow · commit d5a595c6f2b9 · 2024-11-30T08:50:12.000Z
When targeting the Python Stable ABI on Windows (by setting the Py_LIMITED_API macro to a Python minimum version hex), the unversioned python3.lib needs to be linked instead of the versioned one (e.g. python38.lib for Python 3.8). Python's own config sets the library to link by default in a header called pyconfig.h (https://github.com/python/cpython/blob/9cc9e277254023c0ca08e1a9e379fd89475ca9c2/PC/pyconfig.h#L270), which prompts the linker to search for python3.lib if a stable ABI extension is built using `@rules_python` toolchains. Since this library is not exported on Windows in the `python_repository()` rule, building Python C++ extensions with rules_python toolchains fails in the linking step, because the library is never copied. Consequently, it is added now to allow Python SABI extensions to be built (and linked) on Windows with `@rules_python`. Since Python takes responsibility for linking the correct lib on Windows, and never both at the same time, no other changes are made. --------- Co-authored-by: Richard Levasseur <richardlev@gmail.com> Co-authored-by: Richard Levasseur <rlevasseur@google.com>
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -95,6 +95,9 @@ Other changes:
   ([2169](https://github.com/bazelbuild/rules_python/issues/2169)).
 * (workspace) Corrected protobuf's name to com_google_protobuf, the name is
   hardcoded in Bazel, WORKSPACE mode.
+* (repositories): Add libs/python3.lib and pythonXY.dll to the `libpython` target
+  defined by a repository template. This enables stable ABI builds of Python extensions
+  on Windows (by defining Py_LIMITED_API).
 
 {#v0-0-0-added}
 ### Added
diff --git a/python/private/hermetic_runtime_repo_setup.bzl b/python/private/hermetic_runtime_repo_setup.bzl
@@ -89,6 +89,14 @@ def define_hermetic_runtime_toolchain_impl(
         }),
         system_provided = True,
     )
+    cc_import(
+        name = "abi3_interface",
+        interface_library = select({
+            _IS_FREETHREADED: "libs/python3t.lib",
+            "//conditions:default": "libs/python3.lib",
+        }),
+        system_provided = True,
+    )
 
     native.filegroup(
         name = "includes",
@@ -97,7 +105,7 @@ def define_hermetic_runtime_toolchain_impl(
     cc_library(
         name = "python_headers",
         deps = select({
-            "@bazel_tools//src/conditions:windows": [":interface"],
+            "@bazel_tools//src/conditions:windows": [":interface", ":abi3_interface"],
             "//conditions:default": None,
         }),
         hdrs = [":includes"],
@@ -156,15 +164,22 @@ def define_hermetic_runtime_toolchain_impl(
                 "lib/libpython{major}.{minor}t.dylib".format(**version_dict),
             ],
             ":is_freethreaded_windows": [
-                "python3.dll",
+                "python3t.dll",
+                "python{major}{minor}t.dll".format(**version_dict),
                 "libs/python{major}{minor}t.lib".format(**version_dict),
+                "libs/python3t.lib",
             ],
             "@platforms//os:linux": [
                 "lib/libpython{major}.{minor}.so".format(**version_dict),
                 "lib/libpython{major}.{minor}.so.1.0".format(**version_dict),
             ],
             "@platforms//os:macos": ["lib/libpython{major}.{minor}.dylib".format(**version_dict)],
-            "@platforms//os:windows": ["python3.dll", "libs/python{major}{minor}.lib".format(**version_dict)],
+            "@platforms//os:windows": [
+                "python3.dll",
+                "python{major}{minor}.dll".format(**version_dict),
+                "libs/python{major}{minor}.lib".format(**version_dict),
+                "libs/python3.lib",
+            ],
         }),
     )
 
diff --git a/tests/cc/current_py_cc_libs/BUILD.bazel b/tests/cc/current_py_cc_libs/BUILD.bazel
@@ -33,3 +33,21 @@ cc_test(
         "@rules_python//python/cc:current_py_cc_libs",
     ],
 )
+
+# This is technically a headers test, but since the pyconfig.h header
+# designates the appropriate lib to link on Win+MSVC, this test verifies that
+# the expected Windows libraries are all present in the expected location.
+# Since we define the Py_LIMITED_API macro, we expect the linker to go search
+# for libs/python3.lib.
+# buildifier: disable=native-cc
+cc_test(
+    name = "python_libs_linking_windows_test",
+    srcs = ["python_libs_linking_test.cc"],
+    defines = ["Py_LIMITED_API=0x030A0000"],
+    env = {"HELLO": "world"},
+    target_compatible_with = ["@platforms//os:windows"],
+    deps = [
+        "@rules_python//python/cc:current_py_cc_headers",
+        "@rules_python//python/cc:current_py_cc_libs",
+    ],
+)
diff --git a/tests/cc/current_py_cc_libs/python_libs_linking_test.cc b/tests/cc/current_py_cc_libs/python_libs_linking_test.cc
@@ -12,7 +12,7 @@ int main(int argc, char** argv) {
   // To make it actually run, more custom initialization is necessary.
   // See https://docs.python.org/3/c-api/intro.html#embedding-python
   Py_Initialize();
-  PyRun_SimpleString("print('Hello, world')\n");
+  Py_BytesMain(argc, argv);
   Py_Finalize();
   return 0;
 }

Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,7 @@ int main(int argc, char** argv) {`
`12`	`12`	`// To make it actually run, more custom initialization is necessary.`
`13`	`13`	`// See https://docs.python.org/3/c-api/intro.html#embedding-python`
`14`	`14`	`Py_Initialize();`
`15`		`- PyRun_SimpleString("print('Hello, world')\n");`
	`15`	`+ Py_BytesMain(argc, argv);`
`16`	`16`	`Py_Finalize();`
`17`	`17`	`return 0;`
`18`	`18`	`}`