Added version to rust_toolchain (#3952)

Author: UebelAndre

rust/private/repository_utils.bzl

@@ -368,6 +368,7 @@ rust_toolchain(
     extra_exec_rustc_flags = {extra_exec_rustc_flags},
     opt_level = {opt_level},
     strip_level = {strip_level},
+    version = "{version}",
     tags = ["rust_version={version}"],
 )
 """

rust/toolchain.bzl

@@ -611,6 +611,7 @@ def _rust_toolchain_impl(ctx):
         target_os = target_os,
         target_abi = target_abi,
         target_triple = target_triple,
+        version = ctx.attr.version,
         require_explicit_unstable_features = _require_explicit_unstable_features(ctx),
 
         # Experimental and incompatible flags
@@ -842,6 +843,10 @@ rust_toolchain = rule(
                 "For more details see: https://docs.bazel.build/versions/master/skylark/rules.html#configurations"
             ),
         ),
+        "version": attr.string(
+            doc = "The version of the Rust compiler. (E.g. `1.94.1`, nightly/2026-03-26`)",
+            default = "",
+        ),
         "_codegen_units": attr.label(
             default = Label("//rust/settings:codegen_units"),
         ),