Make static linking for nanobind_extension optional (#7)

build_defs.bzl

@@ -15,7 +15,7 @@ load("@nanobind_bazel//:helpers.bzl", "extension_name")
 
 NANOBIND_COPTS = select({
     Label("@rules_cc//cc/compiler:msvc-cl"): [],
-    "//conditions:default": ["-fexceptions", "-fvisibility=hidden"],
+    "//conditions:default": ["-fexceptions", "-fno-strict-aliasing"],
 })
 
 NANOBIND_FEATURES = [
@@ -31,8 +31,10 @@ NANOBIND_DEPS = [
 # A C++ Python extension library built with nanobind.
 # Given a name $NAME, defines the following targets:
 # 1. $NAME.so, a shared object library for use on Linux/Mac.
-# 2. $NAME.pyd, a copy of $NAME.so for use on Windows.
-# 3. $NAME, an alias pointing to the appropriate library
+# 2. $NAME.abi3.so, a copy of $NAME.so for Linux/Mac,
+#     indicating that it is compatible with the Python stable ABI.
+# 3. $NAME.pyd, a copy of $NAME.so for use on Windows.
+# 4. $NAME, an alias pointing to the appropriate library
 #    depending on the target platform.
 def nanobind_extension(
         name,
@@ -47,8 +49,7 @@ def nanobind_extension(
         copts = copts + NANOBIND_COPTS,
         features = features + NANOBIND_FEATURES,
         deps = deps + NANOBIND_DEPS,
-        linkshared = True,
-        linkstatic = True,
+        linkshared = True,  # Python extensions need to be shared libs.
         **kwargs
     )
 

helpers.bzl

@@ -14,7 +14,7 @@ def sizedefs():
     })
 
 # Define the Python version hex if stable ABI builds are requested.
-def pyversionhex():
+def py_limited_api():
     return select({
         "@nanobind_bazel//:cp312": ["Py_LIMITED_API=0x030C0000"],
         "@nanobind_bazel//:cp313": ["Py_LIMITED_API=0x030D0000"],

internal_configure.bzl

@@ -22,6 +22,7 @@ def _internal_configure_extension_impl(module_ctx):
         name = "robin_map",
         build_file = "//:robin_map.BUILD",
         strip_prefix = "robin-map-1.2.1",
+        integrity = "sha256-K1TSwd4vc76lxR1dy9ZIE6CMrxv93P3u5Aq3TpWZ6OM=",
         urls = ["https://github.com/Tessil/robin-map/archive/refs/tags/v1.2.1.tar.gz"],
     )
 

nanobind.BUILD

@@ -1,17 +1,27 @@
 """
-A cross-platform nanobind Bazel BUILD.
+A cross-platform nanobind Bazel build.
 Supports size and linker optimizations across all three major operating systems.
-Size optimizations used: -Os, LTO
-Linker optimizations used: LTCG (MSVC on Windows), linker response file (macOS only).
+Size optimizations used: -Os, LTO.
+Linker optimizations used: LTO (clang, gcc) / LTCG (MSVC), linker response file (macOS only).
 """
 
-load("@nanobind_bazel//:helpers.bzl", "pyversionhex", "sizedefs", "sizeopts")
+load("@nanobind_bazel//:helpers.bzl", "py_limited_api", "sizedefs", "sizeopts")
 
 licenses(["notice"])
 
-# TODO: Change this when cleaning up exports later.
 package(default_visibility = ["//visibility:public"])
 
+_NB_DEPS = [
+    "@robin_map",
+    "@rules_python//python/cc:current_py_cc_headers",
+] + select({
+    # we need to link in the Python libs only on Windows to signal to the linker that it
+    # needs to go searching for these symbols at runtime.
+    # TODO: This seems Windows-specific, so change to `@platforms//os:windows`?
+    "@rules_cc//cc/compiler:msvc-cl": ["@rules_python//python/cc:current_py_cc_libs"],
+    "//conditions:default": [],
+})
+
 cc_library(
     name = "nanobind",
     srcs = glob(["src/*.cpp"]),
@@ -28,19 +38,20 @@ cc_library(
         "//conditions:default": [
             "-fexceptions",
             "-flto",
+            "-fno-strict-aliasing",
         ],
     }) + sizeopts(),
-    defines = pyversionhex(),
-    includes = [
-        "ext/robin_map/include",
-        "include",
-    ],
+    defines = py_limited_api(),
+    includes = ["include"],
     linkopts = select({
-        "@rules_cc//cc/compiler:msvc-cl": ["/LTCG"],  # MSVC.
+        "@platforms//os:linux": [
+            "-Wl,--gc-sections",
+        ],
         "@platforms//os:macos": [
             "-Wl,@$(location :cmake/darwin-ld-cpython.sym)",  # Apple.
             "-Wl,-dead_strip",
         ],
+        "@rules_cc//cc/compiler:msvc-cl": ["/LTCG"],  # MSVC.
         "//conditions:default": [],
     }),
     local_defines = sizedefs(),  # sizeopts apply to nanobind only.
@@ -50,8 +61,5 @@ cc_library(
             "src/*.h",
         ],
     ),
-    deps = [
-        "@robin_map",
-        "@rules_python//python/cc:current_py_cc_headers",
-    ],
+    deps = _NB_DEPS,
 )