Move ExecuTorch-specific stuff in shim to shim_et (try #3) (#8647)

In preparation for replacing the checked-in files in shim/ with https://github.com/facebook/buck2-shims-meta as a submodule. The portions of this diff that are not a pure move are:

creation of shim_et/BUCK
symlink shim/tools to shim_et/tools so that fbsource//tools
movement of Android toolchains from shim/BUCK to shim_et/BUCK because they are not present in buck2-shims-meta
edits to .buckconfig
edit to Utils.cmake to point at shim_et// instead of shim//
edit to shim_et/README.md (note that shim/README.md will come back when shim/ is a submodule pointing to buck2-shims-meta)

Author: swolchok

.buckconfig

@@ -8,14 +8,15 @@
   root = .
   prelude = third-party/prelude
   shim = shim
+  shim_et = shim_et
 
 [repository_aliases]
   config = prelude
   ovr_config = prelude
-  toolchains = shim
-  fbcode = shim
-  fbcode_macros = shim
-  fbsource = shim
+  toolchains = shim_et
+  fbcode = shim_et
+  fbcode_macros = shim_et
+  fbsource = shim_et
   buck = shim
 
 [cxx]

build/Utils.cmake

@@ -206,9 +206,9 @@ function(extract_sources sources_file)
 
     if(ANDROID_ABI)
       if("${ANDROID_ABI}" STREQUAL "arm64-v8a")
-        set(target_platforms_arg "--target-platforms=shim//:android-arm64")
+        set(target_platforms_arg "--target-platforms=shim_et//:android-arm64")
       elseif("${ANDROID_ABI}" STREQUAL "x86_64")
-        set(target_platforms_arg "--target-platforms=shim//:android-x86_64")
+        set(target_platforms_arg "--target-platforms=shim_et//:android-x86_64")
       else()
         message(
           FATAL_ERROR

shim/BUCK

@@ -61,26 +61,3 @@ remote_test_execution_toolchain(
     name = "remote_test_execution",
     visibility = ["PUBLIC"],
 )
-
-execution_platform(
-    name = "android-arm64",
-    cpu_configuration = "prelude//cpu:arm64",
-    os_configuration = "prelude//os:android",
-    # REVIEW: not sure if this is correct
-    use_windows_path_separators = host_info().os.is_windows,
-    visibility = ["PUBLIC"],
-)
-
-execution_platform(
-    name = "android-x86_64",
-    cpu_configuration = "prelude//cpu:x86_64",
-    os_configuration = "prelude//os:android",
-    # REVIEW: not sure if this is correct
-    use_windows_path_separators = host_info().os.is_windows,
-    visibility = ["PUBLIC"],
-)
-
-noop_test_toolchain(
-    name = "test",
-    visibility = ["PUBLIC"],
-)

shim/README.md

@@ -0,0 +1,57 @@
+load("@prelude//platforms:defs.bzl", "execution_platform")
+load("@prelude//tests:test_toolchain.bzl", "noop_test_toolchain")
+load("@prelude//toolchains:cxx.bzl", "system_cxx_toolchain")
+load("@prelude//toolchains:genrule.bzl", "system_genrule_toolchain")
+load("@prelude//toolchains:python.bzl", "system_python_bootstrap_toolchain", "system_python_toolchain")
+load("@prelude//toolchains:remote_test_execution.bzl", "remote_test_execution_toolchain")
+
+# Although the non-Android toolchains below are present in shim/BUCK, it appears that we
+# have to duplicate them here or builds won't work.
+system_cxx_toolchain(
+    name = "cxx",
+    cxx_flags = ["-std=c++20"],
+    visibility = ["PUBLIC"],
+)
+
+system_genrule_toolchain(
+    name = "genrule",
+    visibility = ["PUBLIC"],
+)
+
+system_python_toolchain(
+    name = "python",
+    visibility = ["PUBLIC"],
+)
+
+system_python_bootstrap_toolchain(
+    name = "python_bootstrap",
+    visibility = ["PUBLIC"],
+)
+
+execution_platform(
+    name = "android-arm64",
+    cpu_configuration = "prelude//cpu:arm64",
+    os_configuration = "prelude//os:android",
+    # REVIEW: not sure if this is correct
+    use_windows_path_separators = host_info().os.is_windows,
+    visibility = ["PUBLIC"],
+)
+
+execution_platform(
+    name = "android-x86_64",
+    cpu_configuration = "prelude//cpu:x86_64",
+    os_configuration = "prelude//os:android",
+    # REVIEW: not sure if this is correct
+    use_windows_path_separators = host_info().os.is_windows,
+    visibility = ["PUBLIC"],
+)
+
+noop_test_toolchain(
+    name = "test",
+    visibility = ["PUBLIC"],
+)
+
+remote_test_execution_toolchain(
+    name = "remote_test_execution",
+    visibility = ["PUBLIC"],
+)

shim_et/BUCK

@@ -0,0 +1,19 @@
+# buck2 shims
+
+The `shim_et/` subtree helps the Meta-internal buck2 build system also work in the
+open-source repo.
+
+Shims are how open-source buck2 supports a [line
+like](https://github.com/pytorch/executorch/blob/50aa517549d10324147534d91d04a923b76421d6/kernels/optimized/targets.bzl#L1):
+
+```
+load("@fbsource//xplat/executorch/build:runtime_wrapper.bzl", "runtime")
+```
+
+In the open-source repo, `fbsource//xplat` (a Meta-internal root) doesn't exist.
+The `fbsource = shim_et` line in `../.buckconfig` tells buck2 to look in
+[`shim_et/xplat/executorch/build/runtime_wrapper.bzl`](https://github.com/pytorch/executorch/blob/main/shim_et/xplat/executorch/build/runtime_wrapper.bzl)
+instead.
+
+NOTE: `tools` is a symlink to `../shim/tools` because `fbsource//`
+must refer here, but `fbsource//tools` in particular lives in `shim/`.

shim_et/README.md

@@ -0,0 +1 @@
+../shim/tools