miri: added support for MIRI

rust/BUILD.bazel

@@ -11,6 +11,12 @@ toolchain_type(
     name = "toolchain_type",
 )
 
+# Miri needs a separate toolchain contract because it brings a different
+# driver binary, sysroot, and runtime closure than normal rustc compilation.
+toolchain_type(
+    name = "miri_toolchain_type",
+)
+
 alias(
     name = "toolchain",
     actual = "toolchain_type",

rust/defs.bzl

@@ -33,6 +33,11 @@ load(
     "//rust/private:lints.bzl",
     _rust_lint_config = "rust_lint_config",
 )
+load(
+    "//rust/private:miri.bzl",
+    _miri_binary = "miri_binary",
+    _miri_test = "miri_test",
+)
 load(
     "//rust/private:rust.bzl",
     _rust_binary = "rust_binary",
@@ -102,6 +107,14 @@ rust_test = _rust_test
 rust_test_suite = _rust_test_suite
 # See @rules_rust//rust/private:rust.bzl for a complete description.
 
+# Miri rules wrap already-declared Rust targets so they can reuse the existing
+# crate graph instead of re-encoding the full rust_* rule surface.
+miri_test = _miri_test
+# See @rules_rust//rust/private:miri.bzl for a complete description.
+
+miri_binary = _miri_binary
+# See @rules_rust//rust/private:miri.bzl for a complete description.
+
 rust_doc = _rust_doc
 # See @rules_rust//rust/private:rustdoc.bzl for a complete description.
 

rust/private/BUILD.bazel

@@ -1,4 +1,5 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
+load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
 load("//rust/private:rust_analyzer.bzl", "rust_analyzer_detect_sysroot")
 
 # Exported for docs
@@ -31,6 +32,15 @@ bzl_library(
     ],
 )
 
+# This build setting is flipped by the Miri transition so the normal Rust
+# compilation pipeline can rebuild target-side crates against the Miri sysroot
+# without affecting unrelated Rust builds.
+bool_flag(
+    name = "miri_enabled",
+    build_setting_default = False,
+    visibility = ["//visibility:public"],
+)
+
 rust_analyzer_detect_sysroot(
     name = "rust_analyzer_detect_sysroot",
     visibility = ["//visibility:public"],