Enable GCC 10 (#31)

This patch allows the user to specify `--config=gcc10` to compiler the
code.

We need `--features=static_libstdcxx` because the sysroot has a newer
version of libstdc++ than the Ubuntu 18.04. We use Ubuntu 18.04 as
our host system at the moment.

.bazelrc

@@ -6,9 +6,13 @@ build:clang11 --platform_suffix=clang11
 build:clang11 --//build:requested_compiler_flag=clang11
 build:clang14 --platform_suffix=clang14
 build:clang14 --//build:requested_compiler_flag=clang14
+build:gcc10 --platform_suffix=gcc10
+build:gcc10 --//build:requested_compiler_flag=gcc10
+build:gcc10 --features=static_libstdcxx
 
 # Add a generic alias if the user doesn't care about the exact version.
 build:clang --config=clang14
+build:gcc --config=gcc10
 
 # Compile with clang by default
 build --config=clang14

README.md

@@ -31,5 +31,7 @@ Use the following `--config` settings to switch to different compilers.
 | Latest supported Clang | `--config=clang` |
 | Clang 11 | `--config=clang11` |
 | Clang 14 | `--config=clang14` |
+| Latest supported GCC | `--config=gcc` |
+| GCC 10 | `--config=gcc10` |
 
-Note that the sandboxed compilers do not use a sysroot.
+Note that only GCC uses a sysroot.

WORKSPACE

@@ -58,6 +58,33 @@ load("@llvm_14_toolchain//:toolchains.bzl", llvm_14_register_toolchains="llvm_re
 
 llvm_14_register_toolchains()
 
+http_archive(
+    name = "aspect_gcc_toolchain",
+    urls = [
+        "https://github.com/aspect-build/gcc-toolchain/tarball/ac745d4685e2095cc4f057862800f3f0a473c201",
+    ],
+    patches = [
+        "@//:third_party/aspect_gcc_toolchain/0001-Expose-target_settings-and-set-std-c-14.patch",
+    ],
+    patch_args = ["-p1"],
+    sha256 = "e2e12202dd83f67d71101b24554044de25e1625d16b4b56bc453ecaa8f7c6bd0",
+    type = "tar.gz",
+    strip_prefix = "aspect-build-gcc-toolchain-ac745d4",
+)
+
+load("@aspect_gcc_toolchain//toolchain:defs.bzl", "gcc_register_toolchain", "ARCHS")
+load("@aspect_gcc_toolchain//sysroot:flags.bzl", gcc_sysroot_cflags="cflags", gcc_sysroot_cxxflags="cxxflags")
+
+gcc_register_toolchain(
+    name = "gcc_toolchain_x86_64",
+    sysroot_variant = "x86_64",
+    target_arch = ARCHS.x86_64,
+    gcc_version = "10.3.0",
+    target_settings = ["@//build:gcc10_requested"],
+    extra_cflags = gcc_sysroot_cflags,
+    extra_cxxflags = gcc_sysroot_cxxflags,
+)
+
 http_archive(
     name = "com_google_googletest",
     sha256 = "24564e3b712d3eb30ac9a85d92f7d720f60cc0173730ac166f27dda7fed76cb2",

build/BUILD

@@ -6,6 +6,7 @@ string_flag(
     values = [
         "clang11",
         "clang14",
+        "gcc10",
     ],
 )
 
@@ -20,3 +21,9 @@ config_setting(
     flag_values = {"requested_compiler_flag": "clang14"},
     visibility = ["//visibility:public"],
 )
+
+config_setting(
+    name = "gcc10_requested",
+    flag_values = {"requested_compiler_flag": "gcc10"},
+    visibility = ["//visibility:public"],
+)

config/buildkite/pipelines/au-pull-request.yml

@@ -8,3 +8,5 @@ steps:
     command: bazel test --config=clang11 //...:all
   - label: "Clang 14"
     command: bazel test --config=clang14 //...:all
+  - label: "GCC 10"
+    command: bazel test --config=gcc10 //...:all

third_party/aspect_gcc_toolchain/0001-Expose-target_settings-and-set-std-c-14.patch

@@ -0,0 +1,56 @@
+From b26193f526de8e4ea4e1b370f3c9f104222c3d60 Mon Sep 17 00:00:00 2001
+From: Philipp Schrader <[email protected]>
+Date: Tue, 6 Dec 2022 00:17:31 -0800
+Subject: [PATCH] Expose target_settings and set -std=c++14
+
+---
+ toolchain/cc_toolchain_config.bzl | 2 +-
+ toolchain/defs.bzl                | 8 ++++++++
+ 2 files changed, 9 insertions(+), 1 deletion(-)
+
+diff --git a/toolchain/cc_toolchain_config.bzl b/toolchain/cc_toolchain_config.bzl
+index afeef35..517bb4a 100644
+--- a/toolchain/cc_toolchain_config.bzl
++++ b/toolchain/cc_toolchain_config.bzl
+@@ -299,7 +299,7 @@ def _impl(ctx):
+             ),
+             flag_set(
+                 actions = all_cpp_compile_actions + [ACTION_NAMES.lto_backend],
+-                flag_groups = [flag_group(flags = ["-std=c++0x"])],
++                flag_groups = [flag_group(flags = ["-std=c++14"])],
+             ),
+         ],
+     )
+diff --git a/toolchain/defs.bzl b/toolchain/defs.bzl
+index 1420724..2bdb4c8 100644
+--- a/toolchain/defs.bzl
++++ b/toolchain/defs.bzl
+@@ -56,6 +56,7 @@ def _gcc_toolchain_impl(rctx):
+     rctx.file("BUILD.bazel", _TOOLCHAIN_BUILD_FILE_CONTENT.format(
+         gcc_toolchain_workspace_name = rctx.attr.gcc_toolchain_workspace_name,
+         target_compatible_with = str(target_compatible_with),
++        target_settings = str(rctx.attr.target_settings),
+         toolchain_files_repository_name = rctx.attr.toolchain_files_repository_name,
+
+         # Sysroot
+@@ -133,6 +134,12 @@ _FEATURE_ATTRS = {
+         doc = "contraint_values passed to target_compatible_with of the toolchain. {target_arch} is rendered to the target_arch attribute value.",
+         mandatory = False,
+     ),
++    "target_settings": attr.string_list(
++        default = [],
++        doc = "A list of config_settings that must be satisfied by the " +
++            "target configuration in order for this toolchain to be " +
++            "selected during toolchain resolution.",
++    ),
+     "toolchain_files_repository_name": attr.string(
+         doc = "The name of the repository containing the toolchain files.",
+         mandatory = True,
+@@ -551,6 +558,7 @@ fortran_toolchain(
+ toolchain(
+     name = "cc_toolchain",
+     target_compatible_with = {target_compatible_with},
++    target_settings = {target_settings},
+     toolchain = ":_cc_toolchain",
+     toolchain_type = "@bazel_tools//tools/cpp:toolchain_type",
+ )