[bazel] Fix and update emscripten_toolchain

* Removes `asm` CPU target.
* [feat] Add `wasm32` and `wasm64` CPU targets.
* Fix static library linker flags.
* Use the new `platform` API for toolchains
* Add a `emsdk_register_toolchains` for Platform toolchains.

Author: jrandolf

bazel/.bazelrc

@@ -1,3 +1 @@
-build:wasm --crosstool_top=//emscripten_toolchain:everything
-build:wasm --cpu=wasm
-build:wasm --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
+build:wasm32 --incompatible_enable_cc_toolchain_resolution

bazel/BUILD

@@ -1,5 +1,19 @@
 package(default_visibility = ["//visibility:public"])
 
+platform(
+    name = "cpu_wasm32",
+    constraint_values = [
+        "@platforms//cpu:wasm32",
+    ],
+)
+
+platform(
+    name = "cpu_wasm64",
+    constraint_values = [
+        "@platforms//cpu:wasm64",
+    ],
+)
+
 filegroup(name = "empty")
 
 alias(

bazel/README.md

@@ -17,6 +17,9 @@ emsdk_deps()
 
 load("@emsdk//:emscripten_deps.bzl", emsdk_emscripten_deps = "emscripten_deps")
 emsdk_emscripten_deps(emscripten_version = "2.0.31")
+
+load("@emsdk//:toolchains.bzl", "emsdk_register_toolchains")
+emsdk_register_toolchains()
 ```
 The SHA1 hash in the above `strip_prefix` and `url` parameters correspond to the git revision of
 [emsdk 2.0.31](https://github.com/emscripten-core/emsdk/releases/tag/2.0.31). To get access to
@@ -26,7 +29,6 @@ parameter of `emsdk_emscripten_deps()`. Supported versions are listed in `revisi
 
 ## Building
 
-### Using wasm_cc_binary (preferred)
 First, write a new rule wrapping your `cc_binary`.
 
 ```
@@ -54,17 +56,3 @@ and all of its dependencies, and does not require amending `.bazelrc`. This
 is the preferred way, since it also unpacks the resulting tarball.
 
 See `test_external/` for an example using [embind](https://emscripten.org/docs/porting/connecting_cpp_and_javascript/embind.html).
-
-### Using --config=wasm
-
-Put the following lines into your `.bazelrc`:
-```
-build:wasm --crosstool_top=@emsdk//emscripten_toolchain:everything
-build:wasm --cpu=wasm
-build:wasm --host_crosstool_top=@bazel_tools//tools/cpp:toolchain
-```
-
-Simply pass `--config=wasm` when building a normal `cc_binary`. The result of
-this build will be a tar archive containing any files produced by emscripten.
-See the [Bazel documentation](https://docs.bazel.build/versions/main/tutorial/cc-toolchain-config.html)
-for more details

bazel/WORKSPACE

@@ -7,3 +7,7 @@ deps()
 load(":emscripten_deps.bzl", "emscripten_deps")
 
 emscripten_deps()
+
+load(":toolchains.bzl", "emsdk_register_toolchains")
+
+emsdk_register_toolchains()

bazel/emscripten_toolchain/BUILD.bazel

@@ -1,4 +1,4 @@
-load(":crosstool.bzl", "emscripten_cc_toolchain_config_rule")
+load(":crosstool.bzl", "emscripten_cc_toolchain_config")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -7,44 +7,53 @@ package(default_visibility = ["//visibility:public"])
 # https://github.com/bazelbuild/rules_nodejs/issues/3375
 node_files = "@nodejs_host//:node_files" if existing_rule("@nodejs_host//:node_files") else "@nodejs//:node_files"
 
+filegroup(
+    name = "all_files",
+    srcs = [
+        ":ar_files",
+        ":compiler_files",
+        ":linker_files",
+    ],
+)
+
 filegroup(
     name = "common_files",
     srcs = [
         "emscripten_config",
-        "env.sh",
         "env.bat",
+        "env.sh",
         node_files,
     ],
 )
 
 filegroup(
     name = "compiler_files",
     srcs = [
-        "emcc.sh",
         "emcc.bat",
-        "@emsdk//:compiler_files",
+        "emcc.sh",
         ":common_files",
+        "@emsdk//:compiler_files",
     ],
 )
 
 filegroup(
     name = "linker_files",
     srcs = [
-        "emcc_link.sh",
         "emcc_link.bat",
+        "emcc_link.sh",
         "link_wrapper.py",
-        "@emsdk//:linker_files",
         ":common_files",
+        "@emsdk//:linker_files",
     ],
 )
 
 filegroup(
     name = "ar_files",
     srcs = [
-        "emar.sh",
         "emar.bat",
-        "@emsdk//:ar_files",
+        "emar.sh",
         ":common_files",
+        "@emsdk//:ar_files",
     ],
 )
 
@@ -53,9 +62,9 @@ filegroup(name = "empty")
 # dlmalloc.bc is implictly added by the emscripten toolchain
 cc_library(name = "malloc")
 
-emscripten_cc_toolchain_config_rule(
-    name = "wasm",
-    cpu = "wasm",
+emscripten_cc_toolchain_config(
+    name = "wasm32_cc_toolchain_config",
+    cpu = "wasm32",
     em_config = "emscripten_config",
     emscripten_binaries = "@emsdk//:compiler_files",
     script_extension = select({
@@ -64,26 +73,59 @@ emscripten_cc_toolchain_config_rule(
     }),
 )
 
+emscripten_cc_toolchain_config(
+    name = "wasm64_cc_toolchain_config",
+    cpu = "wasm64",
+    em_config = "emscripten_config",
+    emscripten_binaries = "@emsdk//:compiler_files",
+    script_extension = select({
+        "@bazel_tools//src/conditions:host_windows": "bat",
+        "//conditions:default": "sh",
+    }),
+)
+
+cc_toolchain(
+    name = "wasm32_cc_toolchain",
+    all_files = ":all_files",
+    ar_files = ":ar_files",
+    compiler_files = ":compiler_files",
+    dwp_files = ":empty",
+    linker_files = ":linker_files",
+    objcopy_files = ":empty",
+    strip_files = ":empty",
+    toolchain_config = ":wasm32_cc_toolchain_config",
+    toolchain_identifier = "emscripten-wasm",
+)
+
 cc_toolchain(
-    name = "cc-compiler-wasm",
-    all_files = ":empty",
+    name = "wasm64_cc_toolchain",
+    all_files = ":all_files",
     ar_files = ":ar_files",
-    as_files = ":empty",
     compiler_files = ":compiler_files",
     dwp_files = ":empty",
     linker_files = ":linker_files",
     objcopy_files = ":empty",
     strip_files = ":empty",
-    toolchain_config = "wasm",
+    toolchain_config = ":wasm64_cc_toolchain_config",
     toolchain_identifier = "emscripten-wasm",
 )
 
-cc_toolchain_suite(
-    name = "everything",
-    toolchains = {
-        "wasm": ":cc-compiler-wasm",
-        "wasm|emscripten": ":cc-compiler-wasm",
-    },
+toolchain(
+    name = "cc_wasm32_toolchain",
+    target_compatible_with = [
+        "@platforms//cpu:wasm32",
+    ],
+    toolchain = ":wasm32_cc_toolchain",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+)
+
+toolchain(
+    name = "cc_wasm64_toolchain",
+    target_compatible_with = [
+        "@platforms//cpu:wasm64",
+    ],
+    toolchain = ":wasm64_cc_toolchain",
+    toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
 )
 
 py_binary(

bazel/emscripten_toolchain/crosstool.bzl

@@ -54,22 +54,18 @@ CROSSTOOL_DEFAULT_WARNINGS = [
     "-Wall",
 ]
 
-def _impl(ctx):
+def _emscripten_cc_toolchain_config(ctx):
     target_cpu = ctx.attr.cpu
     toolchain_identifier = "emscripten-" + target_cpu
     target_system_name = target_cpu + "-unknown-emscripten"
 
-    host_system_name = "i686-unknown-linux-gnu"
-
     target_libc = "musl/js"
 
     abi_version = "emscripten_syscalls"
 
     compiler = "emscripten"
     abi_libc_version = "default"
 
-    cc_target_os = "emscripten"
-
     emscripten_dir = ctx.attr.emscripten_binaries.label.workspace_root
 
     builtin_sysroot = emscripten_dir + "/emscripten/cache/sysroot"
@@ -150,8 +146,9 @@ def _impl(ctx):
         flag_sets = [
             flag_set(
                 flag_groups = [
+                    flag_group(flags = ["rcsD"]),
                     flag_group(
-                        flags = ["rcsD", "%{output_execpath}"],
+                        flags = ["%{output_execpath}"],
                         expand_if_available = "output_execpath",
                     ),
                 ],
@@ -323,11 +320,11 @@ def _impl(ctx):
             implies = ["crosstool_cpu_" + target_cpu],
         ),
         feature(
-            name = "crosstool_cpu_asmjs",
+            name = "crosstool_cpu_wasm64",
             provides = ["variant:crosstool_cpu"],
         ),
         feature(
-            name = "crosstool_cpu_wasm",
+            name = "crosstool_cpu_wasm32",
             provides = ["variant:crosstool_cpu"],
         ),
 
@@ -409,7 +406,6 @@ def _impl(ctx):
         feature(name = "emcc_debug_link"),
         feature(
             name = "llvm_backend",
-            requires = [feature_set(features = ["crosstool_cpu_wasm"])],
             enabled = True,
         ),
 
@@ -523,8 +519,8 @@ def _impl(ctx):
         # Emscripten-specific settings:
         flag_set(
             actions = all_compile_actions + all_link_actions,
-            flags = ["-s", "WASM=0"],
-            features = ["crosstool_cpu_asmjs"],
+            flags = ["-s", "MEMORY64=1"],
+            features = ["crosstool_cpu_wasm64"],
         ),
         flag_set(
             actions = all_compile_actions +
@@ -1087,7 +1083,6 @@ def _impl(ctx):
         artifact_name_patterns = artifact_name_patterns,
         cxx_builtin_include_directories = cxx_builtin_include_directories,
         toolchain_identifier = toolchain_identifier,
-        host_system_name = host_system_name,
         target_system_name = target_system_name,
         target_cpu = target_cpu,
         target_libc = target_libc,
@@ -1097,15 +1092,14 @@ def _impl(ctx):
         tool_paths = tool_paths,
         make_variables = make_variables,
         builtin_sysroot = builtin_sysroot,
-        cc_target_os = cc_target_os,
     )
 
-emscripten_cc_toolchain_config_rule = rule(
-    implementation = _impl,
+emscripten_cc_toolchain_config = rule(
+    implementation = _emscripten_cc_toolchain_config,
     attrs = {
-        "cpu": attr.string(mandatory = True, values = ["asmjs", "wasm"]),
+        "cpu": attr.string(mandatory = True, values = ["wasm32", "wasm64"]),
         "em_config": attr.label(mandatory = True, allow_single_file = True),
-        "emscripten_binaries": attr.label(mandatory = True),
+        "emscripten_binaries": attr.label(mandatory = True, cfg = "exec"),
         "script_extension": attr.string(mandatory = True, values = ["sh", "bat"]),
     },
     provides = [CcToolchainConfigInfo],

bazel/emscripten_toolchain/wasm_cc_binary.bzl

@@ -32,7 +32,7 @@ def _wasm_transition_impl(settings, attr):
         "//command_line_option:features": features,
         "//command_line_option:dynamic_mode": "off",
         "//command_line_option:linkopt": linkopts,
-        "//command_line_option:platforms": [],
+        "//command_line_option:platforms": ["@emsdk//:cpu_wasm32", "@emsdk//:cpu_wasm64"],
         "//command_line_option:custom_malloc": "@emsdk//emscripten_toolchain:malloc",
     }
 

bazel/test_external/WORKSPACE

@@ -10,3 +10,7 @@ deps()
 load("@emsdk//:emscripten_deps.bzl", "emscripten_deps")
 
 emscripten_deps()
+
+load("@emsdk//:toolchains.bzl", "emsdk_register_toolchains")
+
+emsdk_register_toolchains()

bazel/toolchains.bzl

@@ -0,0 +1,3 @@
+def emsdk_register_toolchains():
+    native.register_toolchains("//emscripten_toolchain:cc_wasm32_toolchain")
+    native.register_toolchains("//emscripten_toolchain:cc_wasm64_toolchain")