Add freestanding wasm toolchain

MODULE.bazel

@@ -54,6 +54,7 @@ register_toolchains(
 
     # wasm/wasi toolchains
     "@zig_sdk//toolchain:wasip1_wasm",
+    "@zig_sdk//toolchain:none_wasm",
 
     # zig toolchains
     "@zig_sdk//toolchain:zig",

toolchain/platform/defs.bzl

@@ -16,6 +16,7 @@ def declare_platforms():
 
     # We can support GOARCH=wasm32 after https://github.com/golang/go/issues/63131
     declare_platform("wasm", "wasm32", "wasi", "wasip1")
+    declare_platform("wasm", "wasm32", "none", "none")
 
 def declare_libc_aware_platforms():
     # create @zig_sdk//{os}_{arch}_platform entries with zig and go conventions

toolchain/private/defs.bzl

@@ -49,6 +49,7 @@ def target_structs():
         for glibc in _GLIBCS:
             ret.append(_target_linux_gnu(gocpu, zigcpu, glibc))
     ret.append(_target_wasm())
+    ret.append(_target_wasm_no_wasi())
     return ret
 
 def _target_macos(gocpu, zigcpu):
@@ -235,6 +236,37 @@ def _target_wasm():
         ],
     )
 
+def _target_wasm_no_wasi():
+    return struct(
+        gotarget = "none_wasm",
+        zigtarget = "wasm32-freestanding-musl",
+        includes = [] + _INCLUDE_TAIL,
+        linkopts = [],
+        dynamic_library_linkopts = [],
+        supports_dynamic_linker = False,
+        copts = [],
+        libc = "musl",
+        bazel_target_cpu = "wasm32",
+        constraint_values = [
+            "@platforms//os:none",
+            "@platforms//cpu:wasm32",
+        ],
+        ld_zig_subcmd = "wasm-ld",
+        # .wasm extension supported in bazel >= 6.4.0
+        artifact_name_patterns = [
+            {
+                "category_name": "dynamic_library",
+                "prefix": "",
+                "extension": ".wasm",
+            },
+            {
+                "category_name": "executable",
+                "prefix": "",
+                "extension": ".wasm",
+            },
+        ],
+    )
+
 def transform_os_name(os):
     if os.startswith("mac os"):
         return "macos"

toolchain/zig-wrapper.zig

@@ -283,7 +283,7 @@ fn getRunMode(self_exe: []const u8, self_base_noexe: []const u8) error{BadParent
         return error.BadParent;
 
     const got_os = it.next() orelse return error.BadParent;
-    if (mem.indexOf(u8, "linux,macos,windows,wasi", got_os) == null)
+    if (mem.indexOf(u8, "linux,macos,windows,wasi,freestanding", got_os) == null)
         return error.BadParent;
 
     // ABI triple is too much of a moving target