build: vendor Rust crate dependencies

third_party/crates/alias_rules.bzl

@@ -0,0 +1,47 @@
+"""Alias that transitions its target to `compilation_mode=opt`.  Use `transition_alias="opt"` to enable."""
+
+load("@rules_cc//cc:defs.bzl", "CcInfo")
+load("@rules_rust//rust:rust_common.bzl", "COMMON_PROVIDERS")
+
+def _transition_alias_impl(ctx):
+    # `ctx.attr.actual` is a list of 1 item due to the transition
+    providers = [ctx.attr.actual[0][provider] for provider in COMMON_PROVIDERS]
+    if CcInfo in ctx.attr.actual[0]:
+        providers.append(ctx.attr.actual[0][CcInfo])
+    return providers
+
+def _change_compilation_mode(compilation_mode):
+    def _change_compilation_mode_impl(_settings, _attr):
+        return {
+            "//command_line_option:compilation_mode": compilation_mode,
+        }
+
+    return transition(
+        implementation = _change_compilation_mode_impl,
+        inputs = [],
+        outputs = [
+            "//command_line_option:compilation_mode",
+        ],
+    )
+
+def _transition_alias_rule(compilation_mode):
+    return rule(
+        implementation = _transition_alias_impl,
+        provides = COMMON_PROVIDERS,
+        attrs = {
+            "actual": attr.label(
+                mandatory = True,
+                doc = "`rust_library()` target to transition to `compilation_mode=opt`.",
+                providers = COMMON_PROVIDERS,
+                cfg = _change_compilation_mode(compilation_mode),
+            ),
+            "_allowlist_function_transition": attr.label(
+                default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+            ),
+        },
+        doc = "Transitions a Rust library crate to the `compilation_mode=opt`.",
+    )
+
+transition_alias_dbg = _transition_alias_rule("dbg")
+transition_alias_fastbuild = _transition_alias_rule("fastbuild")
+transition_alias_opt = _transition_alias_rule("opt")