llvm_toolchain: add compiler_rt for wasm32/wasi

Author: rrbutani

toolchain/internal/configure.bzl

@@ -15,6 +15,7 @@
 load(
     "@com_grail_bazel_toolchain//toolchain/internal:extra_targets.bzl",
     _cpu_names = "cpu_names",
+    _extra_target_setup = "extra_target_setup",
     _overrides_for_target = "overrides_for_target",
     _split_target_triple = "split_target_triple",
     _target_triple_to_constraints = "target_triple_to_constraints",
@@ -296,6 +297,10 @@ def llvm_register_toolchains():
     if not _download_llvm(rctx):
         _download_llvm_preconfigured(rctx)
 
+    # Finally, do additional set up for the extra targets:
+    for target in rctx.attr.extra_targets:
+        _extra_target_setup(rctx, target)
+
 def conditional_cc_toolchain(
     name,
     toolchain_config,

toolchain/internal/extra_targets.bzl

@@ -391,7 +391,17 @@ def sysroot_for_target(rctx, triple):
 
         return None
 
+# Runs *after* the toolchain has been fetched and extracted.
 def extra_target_setup(rctx, triple):
     arch, _vendor, os, _env = split_target_triple(triple)
 
-
+    # TODO: I think compiler_rt for wasi can be used on
+    # `wasm32-unknown-unknown` too.
+    if arch == "wasm32" and (os == "wasi" or os == "unknown" or os == "none"):
+        install_wasi_compiler_rt(rctx)
+    else:
+        print(
+            ("`{}` support has not been added to bazel-toolchain; you may " +
+            "need to grab compiler_rt or do additional toolchain setup " +
+            "yourself!" + README).format(triple)
+        )

toolchain/internal/extra_targets/wasi.bzl

@@ -54,7 +54,7 @@ def get_wasi_sysroot(rctx):
         )
 
         print(
-            "\n\nIt worked! Feel free to make a PR adding `{}` as the WASI URL for LLVM {} with sha256 = `{}`.\n\n".format(
+            "\n\nIt worked! Feel free to make a PR adding `{}` as the WASI sysroot URL for LLVM {} with sha256 = `{}`.\n\n".format(
                 url,
                 llvm_major_version,
                 res.sha256
@@ -104,4 +104,34 @@ def wasi_compiler_rt_url(llvm_major_version):
     return "https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-{v}/libclang_rt.builtins-wasm32-wasi-{v}.0.tar.gz".format(v = llvm_major_version)
 
 def install_wasi_compiler_rt(rctx):
-    pass
+    llvm_version = rctx.attr.llvm_version
+    llvm_major_version = int(llvm_version.split(".")[0])
+    common_download_params = {
+        "output": "lib/clang/{}/lib/wasi".format(llvm_version),
+        "stripPrefix": "lib/wasi",
+        "canonical_id": str(llvm_major_version),
+    }
+
+    if llvm_major_version in WASI_COMPILER_RT_LINKS:
+        url, sha = WASI_COMPILER_RT_LINKS[llvm_major_version]
+        rctx.download_and_extract(
+            url = url,
+            sha256 = sha,
+            **common_download_params
+        )
+    else:
+        url = wasi_compiler_rt_url(llvm_major_version)
+        print("We don't have a WASI compiler_rt URL for LLVM {}; we'll try to use `{}`..".format(llvm_major_version, url))
+
+        res = rctx.download_and_extract(
+            url = url,
+            **common_download_params
+        )
+
+        print(
+            "\n\nIt worked! Feel free to make a PR adding `{}` as the WASI compiler_rt URL for LLVM {} with sha256 = `{}`.\n\n".format(
+                url,
+                llvm_major_version,
+                res.sha256
+            )
+        )