Add -ffile-prefix-map for deterministic C++ compilation

Summary:
Previously, with some toolchains, the debuginfo in object files produced by `cxx_compile` actions contained absolute paths for headers in the toolchain's standard library. This affected xplat's `minimal_xcode` toolchain.

Different macOS RE runners do not necessarily all put the current directory in the same location when running actions, which introduced nondeterminism and wrecks cache utilization.

Reviewed By: rmaz

Differential Revision: D60678938

fbshipit-source-id: a8bfab64d39571a3bd5e7b3fb4ae16a977a7c3cf

cxx/compile.bzl

@@ -608,14 +608,15 @@ def _get_category(ext: CxxExtension) -> str:
         # This should be unreachable as long as we handle all enum values
         fail("Unknown extension: " + ext.value)
 
-def _get_compile_base(compiler_info: typing.Any) -> cmd_args:
+def _get_compile_base(toolchain: CxxToolchainInfo, compiler_info: typing.Any) -> cmd_args:
     """
     Given a compiler info returned by _get_compiler_info, form the base compile args.
     """
 
-    cmd = cmd_args(compiler_info.compiler)
-
-    return cmd
+    if toolchain.remap_cwd and compiler_info.compiler_type in ["clang", "clang_windows", "clang_cl"]:
+        return cmd_args(toolchain.remap_cwd, compiler_info.compiler)
+    else:
+        return cmd_args(compiler_info.compiler)
 
 def _dep_file_type(ext: CxxExtension) -> [DepFileType, None]:
     # Raw assembly doesn't make sense to capture dep files for.
@@ -761,7 +762,7 @@ def _generate_base_compile_command(
     """
     toolchain = get_cxx_toolchain_info(ctx)
     compiler_info = _get_compiler_info(toolchain, ext)
-    base_compile_cmd = _get_compile_base(compiler_info)
+    base_compile_cmd = _get_compile_base(toolchain, compiler_info)
     category = _get_category(ext)
 
     headers_dep_files = None

cxx/cxx_toolchain.bzl

@@ -179,6 +179,7 @@ def cxx_toolchain_impl(ctx):
         dumpbin_toolchain_path = ctx.attrs._dumpbin_toolchain_path[DefaultInfo].default_outputs[0] if ctx.attrs._dumpbin_toolchain_path else None,
         target_sdk_version = get_toolchain_target_sdk_version(ctx),
         dist_lto_tools_info = ctx.attrs.dist_lto_tools[DistLtoToolsInfo],
+        remap_cwd = ctx.attrs._remap_cwd_tool[RunInfo] if ctx.attrs.remap_cwd else None,
     )
 
 def cxx_toolchain_extra_attributes(is_toolchain_rule):
@@ -225,6 +226,7 @@ def cxx_toolchain_extra_attributes(is_toolchain_rule):
         "public_headers_symlinks_enabled": attrs.bool(default = True),
         "ranlib": attrs.option(dep_type(providers = [RunInfo]), default = None),
         "rc_compiler": attrs.option(dep_type(providers = [RunInfo]), default = None),
+        "remap_cwd": attrs.bool(default = False),
         "requires_objects": attrs.bool(default = False),
         "sanitizer_runtime_enabled": attrs.bool(default = False),
         "sanitizer_runtime_files": attrs.set(attrs.dep(), sorted = True, default = []),  # Use `attrs.dep()` as it's not a tool, always propagate target platform
@@ -255,6 +257,7 @@ def cxx_toolchain_extra_attributes(is_toolchain_rule):
         # FIXME: prelude// should be standalone (not refer to fbsource//)
         "_mk_hmap": attrs.default_only(dep_type(providers = [RunInfo], default = "prelude//cxx/tools:hmap_wrapper")),
         "_msvc_hermetic_exec": attrs.default_only(dep_type(providers = [RunInfo], default = "prelude//windows/tools:msvc_hermetic_exec")),
+        "_remap_cwd_tool": attrs.default_only(dep_type(providers = [RunInfo], default = "prelude//cxx/tools:remap_cwd")),
     } | cxx_toolchain_allow_cache_upload_args()
 
 def _cxx_toolchain_inheriting_target_platform_attrs():

cxx/cxx_toolchain_types.bzl

@@ -204,6 +204,7 @@ CxxToolchainInfo = provider(
         "pic_behavior": provider_field(typing.Any, default = None),
         "dumpbin_toolchain_path": provider_field(typing.Any, default = None),
         "target_sdk_version": provider_field([str, None], default = None),
+        "remap_cwd": provider_field(RunInfo | None, default = None),
     },
 )
 
@@ -257,7 +258,8 @@ def cxx_toolchain_infos(
         platform_deps_aliases = [],
         pic_behavior = PicBehavior("supported"),
         dumpbin_toolchain_path = None,
-        target_sdk_version = None):
+        target_sdk_version = None,
+        remap_cwd = None):
     """
     Creates the collection of cxx-toolchain Infos for a cxx toolchain.
 
@@ -301,6 +303,7 @@ def cxx_toolchain_infos(
         pic_behavior = pic_behavior,
         dumpbin_toolchain_path = dumpbin_toolchain_path,
         target_sdk_version = target_sdk_version,
+        remap_cwd = remap_cwd,
     )
 
     # Provide placeholder mappings, used primarily by cxx_genrule.

cxx/tools/BUCK.v2

@@ -54,6 +54,12 @@ prelude.python_bootstrap_binary(
     visibility = ["PUBLIC"],
 )
 
+prelude.python_bootstrap_binary(
+    name = "remap_cwd",
+    main = "remap_cwd.py",
+    visibility = ["PUBLIC"],
+)
+
 # Required to support the $(cxx-header-tree) macro
 cxx_hacks(
     name = "cxx_hacks",

cxx/tools/remap_cwd.py

@@ -0,0 +1,32 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under both the MIT license found in the
+# LICENSE-MIT file in the root directory of this source tree and the Apache
+# License, Version 2.0 found in the LICENSE-APACHE file in the root directory
+# of this source tree.
+
+"""
+Usage: remap_cwd.py path/to/clang++ [args...]
+
+Runs `path/to/clang++ -ffile-prefix-map=$PWD= [args...]`
+"""
+
+import os
+import subprocess
+import sys
+
+
+if __name__ == "__main__":
+    cwd = os.getcwd()
+    # Add trailing slash
+    cwd = os.path.join(cwd, "")
+
+    ret = subprocess.call(
+        [
+            sys.argv[1],
+            f"-ffile-prefix-map={cwd}=",
+            *sys.argv[2:],
+        ],
+    )
+    sys.exit(ret)