From 863eab96c53ac5c8b5281fc9d889d0ac94cb289b Mon Sep 17 00:00:00 2001
From: Nicholas Junge <n.junge@appliedai.de>
Date: Thu, 22 Feb 2024 20:58:57 +0100
Subject: [PATCH] Add --sizeopt flag to `@nanobind` target

Controls the passing of size optimization flags for each target compiler.
Unfortunately, since this needs a `select()` based on compiler and
sizeopt yes/no, we now have to explicitly match the C++ compiler from the
configured toolchain. Also, this results in quite a few config settings
in the `@nanobind` target, which could be adjusted in visibility when
this is more polished.

The current attempt seems to build the nanobind example properly.
---
 MODULE.bazel   |  1 +
 helpers.bzl    |  8 ++++++++
 nanobind.BUILD | 55 +++++++++++++++++++++++++++++++++++++++++++++++---
 3 files changed, 61 insertions(+), 3 deletions(-)
 create mode 100644 helpers.bzl

diff --git a/MODULE.bazel b/MODULE.bazel
index b9080a3..e4ed562 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -6,6 +6,7 @@ module(
 bazel_dep(name = "platforms", version = "0.0.8")
 bazel_dep(name = "rules_cc", version = "0.0.9")
 bazel_dep(name = "rules_python", version = "0.31.0")
+bazel_dep(name = "bazel_skylib", version = "1.5.0")
 
 # Parses the configured nanobind version from this file, and creates a `http_archive` for it.
 # Currently, this points to stable tags only.
diff --git a/helpers.bzl b/helpers.bzl
new file mode 100644
index 0000000..6104e2d
--- /dev/null
+++ b/helpers.bzl
@@ -0,0 +1,8 @@
+"""Helper flags for nanobind build options."""
+
+def sizeopts():
+    return select({
+        "@nanobind//:msvc_and_minsize": ["/Os"],
+        "@nanobind//:nonmsvc_and_minsize": ["-Os"],
+        "@nanobind//:without_sizeopts": [],
+    })
diff --git a/nanobind.BUILD b/nanobind.BUILD
index c90c4fb..9577d20 100644
--- a/nanobind.BUILD
+++ b/nanobind.BUILD
@@ -5,15 +5,62 @@ Size optimizations used: -Os, LTO
 Linker optimizations used: LTCG (MSVC on Windows), linker response file (macOS only).
 """
 
+load("@bazel_skylib//lib:selects.bzl", "selects")
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
+load("@nanobind_bazel//:helpers.bzl", "sizeopts")
+
 licenses(["notice"])
 
+# TODO: Change this when cleaning up exports later.
 package(default_visibility = ["//visibility:public"])
 
+bool_flag(
+    name = "minsize",
+    build_setting_default = False,
+)
+
+config_setting(
+    name = "with_sizeopts",
+    flag_values = {":minsize": "True"},
+)
+
+config_setting(
+    name = "without_sizeopts",
+    flag_values = {":minsize": "False"},
+)
+
 config_setting(
     name = "msvc",
     flag_values = {"@bazel_tools//tools/cpp:compiler": "msvc-cl"},
 )
 
+# Is the currently configured C++ compiler not MSVC?
+selects.config_setting_group(
+    name = "nonmsvc",
+    match_any = [
+        "@rules_cc//cc/compiler:gcc",
+        "@rules_cc//cc/compiler:clang",
+        "@rules_cc//cc/compiler:clang-cl",
+        "@rules_cc//cc/compiler:mingw-gcc",
+    ],
+)
+
+selects.config_setting_group(
+    name = "msvc_and_minsize",
+    match_all = [
+        ":msvc",
+        ":with_sizeopts",
+    ],
+)
+
+selects.config_setting_group(
+    name = "nonmsvc_and_minsize",
+    match_all = [
+        ":nonmsvc",
+        ":with_sizeopts",
+    ],
+)
+
 cc_library(
     name = "nanobind",
     srcs = glob(["src/*.cpp"]),
@@ -24,7 +71,6 @@ cc_library(
     copts = select({
         ":msvc": [
             "/EHsc",  # exceptions
-            "/Os",  # size optimizations
             "/GL",  # LTO / whole program optimization
         ],
         # clang and gcc, across all platforms.
@@ -33,14 +79,17 @@ cc_library(
             "-flto",
             "-Os",
         ],
-    }),
+    }) + sizeopts(),
     includes = [
         "ext/robin_map/include",
         "include",
     ],
     linkopts = select({
         ":msvc": ["/LTCG"],  # MSVC.
-        "@platforms//os:macos": ["-Wl,@$(location :cmake/darwin-ld-cpython.sym)"],  # Apple.
+        "@platforms//os:macos": [
+            "-Wl,@$(location :cmake/darwin-ld-cpython.sym)",  # Apple.
+            "-Wl,-dead_strip",
+        ],
         "//conditions:default": [],
     }),
     textual_hdrs = glob(