Add _experimental_toolchain_generated_sysroot to rustdoc

Author: Vinh Tran

rust/private/rustc.bzl

@@ -965,9 +965,8 @@ def construct_arguments(
     if linker_script:
         rustc_flags.add(linker_script, format = "--codegen=link-arg=-T%s")
 
-    if hasattr(ctx.attr, "_experimental_toolchain_generated_sysroot"):
-        if ctx.attr._experimental_toolchain_generated_sysroot[BuildSettingInfo].value == True:
-            rustc_flags.add("--sysroot", toolchain.sysroot)
+    if attr._experimental_toolchain_generated_sysroot[BuildSettingInfo].value == 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")
@@ -1042,6 +1041,9 @@ def construct_arguments(
             data_paths,
         ))
 
+    # Ensure the sysroot is set for the target platform
+    env["SYSROOT"] = toolchain.sysroot
+
     if toolchain._rename_first_party_crates:
         env["RULES_RUST_THIRD_PARTY_DIR"] = toolchain._third_party_dir
 

rust/private/rustdoc.bzl

@@ -321,6 +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"),