Add --sysroot in rust_toolchain rule instead

Author: Vinh Tran

rust/private/rust.bzl

@@ -609,13 +609,6 @@ _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

@@ -38,7 +38,6 @@ load(
     "make_static_lib_symlink",
     "relativize",
 )
-load("//rust/settings:incompatible.bzl", "IncompatibleFlagInfo")
 
 BuildInfo = _BuildInfo
 
@@ -966,10 +965,6 @@ 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

@@ -321,13 +321,6 @@ 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/toolchain.bzl

@@ -16,6 +16,7 @@ load(
     "find_cc_toolchain",
     "make_static_lib_symlink",
 )
+load("//rust/settings:incompatible.bzl", "IncompatibleFlagInfo")
 
 rust_analyzer_toolchain = _rust_analyzer_toolchain
 rustfmt_toolchain = _rustfmt_toolchain
@@ -537,6 +538,10 @@ def _rust_toolchain_impl(ctx):
     sysroot_path = sysroot.sysroot_anchor.dirname
     sysroot_short_path, _, _ = sysroot.sysroot_anchor.short_path.rpartition("/")
 
+    rustc_flags = ctx.attr.extra_rustc_flags
+    if ctx.attr._experimental_toolchain_generated_sysroot[IncompatibleFlagInfo].enabled == True:
+        rustc_flags = ["--sysroot=" + sysroot_path] + rustc_flags
+
     # Variables for make variable expansion
     make_variables = {
         "RUSTC": sysroot.rustc.path,
@@ -623,7 +628,7 @@ def _rust_toolchain_impl(ctx):
         rustfmt = sysroot.rustfmt,
         staticlib_ext = ctx.attr.staticlib_ext,
         stdlib_linkflags = stdlib_linkflags_cc_info,
-        extra_rustc_flags = ctx.attr.extra_rustc_flags,
+        extra_rustc_flags = rustc_flags,
         extra_exec_rustc_flags = ctx.attr.extra_exec_rustc_flags,
         per_crate_rustc_flags = ctx.attr.per_crate_rustc_flags,
         sysroot = sysroot_path,
@@ -787,6 +792,13 @@ rust_toolchain = rule(
         "_cc_toolchain": attr.label(
             default = Label("@bazel_tools//tools/cpp:current_cc_toolchain"),
         ),
+        "_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."
+            ),
+        ),
         "_experimental_use_coverage_metadata_files": attr.label(
             default = Label("//rust/settings:experimental_use_coverage_metadata_files"),
         ),

test/toolchain/toolchain_test.bzl

@@ -36,16 +36,16 @@ 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",
-    )
+    found_sysroot = False
+
+    for arg in action.argv:
+        if arg.startswith("--sysroot") and arg.endswith("test/toolchain/rust_extra_flags_toolchain"):
+            found_sysroot = True
 
     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",
+        found_sysroot,
+        "Missing --sysroot flag or --sysroot does not point to correct sysroot directory",
     )
 
     return analysistest.end(env)