Set --sysroot to sysroot generated by rust_toolchain

.bazelci/presubmit.yml

@@ -92,8 +92,10 @@ tasks:
     test_targets: *default_linux_targets
     build_flags:
       - "--compilation_mode=opt"
+      - "--@rules_rust//rust/settings:experimental_toolchain_generated_sysroot=True"
     test_flags:
       - "--compilation_mode=opt"
+      - "--@rules_rust//rust/settings:experimental_toolchain_generated_sysroot=True"
   macos_opt:
     name: Opt Mode
     platform: macos

rust/private/rust.bzl

@@ -609,6 +609,13 @@ _common_attrs = {
     "_error_format": attr.label(
         default = Label("//:error_format"),
     ),
+    "_experimental_toolchain_generated_sysroot": attr.label(
+        default = Label("//rust/settings:experimental_toolchain_generated_sysroot"),
+        doc = (
+            "Label to a boolean build setting that lets the rule knows wheter to set --sysroot to rustc" +
+            "This flag is only relevant when used together with --@rules_rust//rust/settings:experimental_toolchain_generated_sysroot."
+        ),
+    ),
     "_extra_exec_rustc_flag": attr.label(
         default = Label("//:extra_exec_rustc_flag"),
     ),

rust/private/rustc.bzl

@@ -38,6 +38,7 @@ load(
     "make_static_lib_symlink",
     "relativize",
 )
+load("//rust/settings:incompatible.bzl", "IncompatibleFlagInfo")
 
 BuildInfo = _BuildInfo
 
@@ -965,6 +966,10 @@ def construct_arguments(
     if linker_script:
         rustc_flags.add(linker_script, format = "--codegen=link-arg=-T%s")
 
+    if hasattr(attr, "_experimental_toolchain_generated_sysroot"):
+        if attr._experimental_toolchain_generated_sysroot[IncompatibleFlagInfo].enabled == True:
+            rustc_flags.add("--sysroot", toolchain.sysroot)
+
     # Tell Rustc where to find the standard library (or libcore)
     rustc_flags.add_all(toolchain.rust_std_paths, before_each = "-L", format_each = "%s")
     rustc_flags.add_all(rust_flags)

rust/private/rustdoc.bzl

@@ -137,10 +137,6 @@ def rustdoc_compile_action(
         if "OUT_DIR" in env:
             env.update({"OUT_DIR": "${{pwd}}/{}".format(build_info.out_dir.short_path)})
 
-        # `rustdoc` does not support the SYSROOT environment variable. To account
-        # for this, the flag must be explicitly passed to the `rustdoc` binary.
-        args.rustc_flags.add(toolchain.sysroot_short_path, format = "--sysroot=${{pwd}}/%s")
-
     return struct(
         executable = ctx.executable._process_wrapper,
         inputs = depset([crate_info.output], transitive = [compile_inputs]),
@@ -325,6 +321,13 @@ rust_doc = rule(
         "_error_format": attr.label(
             default = Label("//:error_format"),
         ),
+        "_experimental_toolchain_generated_sysroot": attr.label(
+            default = Label("//rust/settings:experimental_toolchain_generated_sysroot"),
+            doc = (
+                "Label to a boolean build setting that lets the rule knows wheter to set --sysroot to rustc" +
+                "This flag is only relevant when used together with --@rules_rust//rust/settings:experimental_toolchain_generated_sysroot."
+            ),
+        ),
         "_process_wrapper": attr.label(
             doc = "A process wrapper for running rustdoc on all platforms",
             default = Label("@rules_rust//util/process_wrapper"),

rust/settings/BUILD.bazel

@@ -1,5 +1,6 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
 load("@bazel_skylib//rules:common_settings.bzl", "bool_flag", "string_flag")
+load(":incompatible.bzl", "incompatible_flag")
 
 package(default_visibility = ["//visibility:public"])
 
@@ -63,3 +64,10 @@ bzl_library(
     name = "bzl_lib",
     srcs = glob(["**/*.bzl"]),
 )
+
+# A flag to set rustc --sysroot flag to the sysroot generated by rust_toolchain
+incompatible_flag(
+    name = "experimental_toolchain_generated_sysroot",
+    build_setting_default = False,
+    issue = "https://github.com/bazelbuild/rules_rust/issues/2039",
+)

test/toolchain/toolchain_test.bzl

@@ -36,12 +36,25 @@ def _toolchain_adds_rustc_flags_impl(ctx):
         "Found exec toolchain flag ({}) in rustc flags: {}".format(EXEC_TOOLCHAIN_FLAG, action.argv),
     )
 
+    asserts.true(
+        env,
+        "--sysroot" in action.argv,
+        "Missing --sysroot flag",
+    )
+
+    asserts.true(
+        env,
+        action.argv[action.argv.index("--sysroot") + 1].endswith("test/toolchain/rust_extra_flags_toolchain"),
+        "--sysroot does not set to directory generated by rust_toolchain",
+    )
+
     return analysistest.end(env)
 
 toolchain_adds_rustc_flags_test = analysistest.make(
     _toolchain_adds_rustc_flags_impl,
     config_settings = {
         str(Label("//:extra_rustc_flags")): [CONFIG_FLAG],
+        str(Label("//rust/settings:experimental_toolchain_generated_sysroot")): True,
     },
 )