Platform transition added to Rust binary rules. (#2310)

Without much insight into core Bazel's plans for supporting "flagless" builds across platforms, this seems like the most direct way to select the platform for a given Rust binary target (all the terminal rules) that doesn't need additional work to forward providers. Currently I'm using `platform_transition_binary` (https://github.com/aspect-build/bazel-lib/blob/main/docs/transitions.md), but it doesn't work with Rust Analyzer/Clippy/etc. presumably due to not forwarding the providers. In the case of this particular rule, it also doesn't work for something like `rust_shared_library()` which is explicitly not an `executable = True` target. @illicitonion brought to my attention `with_cfg` (https://github.com/fmeum/with_cfg.bzl) which could be used as an alternative by consumers of `rules_rust` instead of this PR. That feels reasonable, though certainly more work for individual users and appears to rely on a lot of Bazel black magic. Along the same lines, this could wait on rule inheritance as presumably a more formally supported `with_cfg` approach, which would also be up to individual users and not `rules_rust`.
bazelbuild · Dec 13, 2023 · 0e4be00 · 0e4be00
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diff --git a/docs/defs.md b/docs/defs.md
diff --git a/docs/flatten.md b/docs/flatten.md
diff --git a/examples/nix_cross_compiling/BUILD.bazel b/examples/nix_cross_compiling/BUILD.bazel
@@ -1,150 +1,29 @@
 load("@bazel_skylib//rules:build_test.bzl", "build_test")
-load("//bazel:transitions.bzl", "platform_transition_binary")
 
 # Disabled targets need the user to supply a sysroot in `flake.nix` first.
 
 build_test(
     name = "nix_cross_compiling",
     targets = [
-        # ":cc_binary_aarch64-apple-darwin",
-        # ":cc_binary_aarch64-apple-ios",
-        ":cc_binary_aarch64-linux-android",
-        ":cc_binary_aarch64-unknown-linux-gnu",
-        ":cc_binary_wasm32-unknown-unknown",
-        ":cc_binary_wasm32-wasi",
-        # ":cc_binary_x86_64-apple-darwin",
-        # ":cc_binary_x86_64-pc-windows-msvc",
-        ":cc_binary_x86_64-unknown-linux-gnu",
-        ":cc_binary_x86_64-unknown-nixos-gnu",
-        # ":rust_binary_aarch64-apple-darwin",
-        # ":rust_binary_aarch64-apple-ios",
-        ":rust_binary_aarch64-linux-android",
-        ":rust_binary_aarch64-unknown-linux-gnu",
-        ":rust_binary_wasm32-unknown-unknown",
-        ":rust_binary_wasm32-wasi",
-        # ":rust_binary_x86_64-apple-darwin",
-        # ":rust_binary_x86_64-pc-windows-msvc",
-        ":rust_binary_x86_64-unknown-linux-gnu",
-        ":rust_binary_x86_64-unknown-nixos-gnu",
+        # "//cc_binary:cc_binary_aarch64-apple-darwin",
+        # "//cc_binary:cc_binary_aarch64-apple-ios",
+        "//cc_binary:cc_binary_aarch64-linux-android",
+        "//cc_binary:cc_binary_aarch64-unknown-linux-gnu",
+        "//cc_binary:cc_binary_wasm32-unknown-unknown",
+        "//cc_binary:cc_binary_wasm32-wasi",
+        # "//cc_binary:cc_binary_x86_64-apple-darwin",
+        # "//cc_binary:cc_binary_x86_64-pc-windows-msvc",
+        "//cc_binary:cc_binary_x86_64-unknown-linux-gnu",
+        "//cc_binary:cc_binary_x86_64-unknown-nixos-gnu",
+        # "//rust_binary:rust_binary_aarch64-apple-darwin",
+        # "//rust_binary:rust_binary_aarch64-apple-ios",
+        "//rust_binary:rust_binary_aarch64-linux-android",
+        "//rust_binary:rust_binary_aarch64-unknown-linux-gnu",
+        "//rust_binary:rust_binary_wasm32-unknown-unknown",
+        "//rust_binary:rust_binary_wasm32-wasi",
+        # "//rust_binary:rust_binary_x86_64-apple-darwin",
+        # "//rust_binary:rust_binary_x86_64-pc-windows-msvc",
+        "//rust_binary:rust_binary_x86_64-unknown-linux-gnu",
+        "//rust_binary:rust_binary_x86_64-unknown-nixos-gnu",
     ],
 )
-
-# platform_transition_binary(
-#     name = "cc_binary_aarch64-apple-darwin",
-#     binary = "//cc_binary",
-#     target_platform = "//bazel/platforms:aarch64-apple-darwin",
-# )
-
-# platform_transition_binary(
-#     name = "cc_binary_aarch64-apple-ios",
-#     binary = "//cc_binary",
-#     target_platform = "//bazel/platforms:aarch64-apple-ios",
-# )
-
-platform_transition_binary(
-    name = "cc_binary_aarch64-linux-android",
-    binary = "//cc_binary",
-    target_platform = "//bazel/platforms:aarch64-linux-android",
-)
-
-platform_transition_binary(
-    name = "cc_binary_aarch64-unknown-linux-gnu",
-    binary = "//cc_binary",
-    target_platform = "//bazel/platforms:aarch64-unknown-linux-gnu",
-)
-
-platform_transition_binary(
-    name = "cc_binary_wasm32-unknown-unknown",
-    binary = "//cc_binary",
-    target_platform = "//bazel/platforms:wasm32-unknown-unknown",
-)
-
-platform_transition_binary(
-    name = "cc_binary_wasm32-wasi",
-    binary = "//cc_binary",
-    target_platform = "//bazel/platforms:wasm32-wasi",
-)
-
-# platform_transition_binary(
-#     name = "cc_binary_x86_64-apple-darwin",
-#     binary = "//cc_binary",
-#     target_platform = "//bazel/platforms:x86_64-apple-darwin",
-# )
-
-# platform_transition_binary(
-#     name = "cc_binary_x86_64-pc-windows-msvc",
-#     binary = "//cc_binary",
-#     target_platform = "//bazel/platforms:x86_64-pc-windows-msvc",
-# )
-
-platform_transition_binary(
-    name = "cc_binary_x86_64-unknown-linux-gnu",
-    binary = "//cc_binary",
-    target_platform = "//bazel/platforms:x86_64-unknown-linux-gnu",
-)
-
-platform_transition_binary(
-    name = "cc_binary_x86_64-unknown-nixos-gnu",
-    binary = "//cc_binary",
-    target_platform = "//bazel/platforms:x86_64-unknown-nixos-gnu",
-)
-
-# platform_transition_binary(
-#     name = "rust_binary_aarch64-apple-darwin",
-#     binary = "//rust_binary",
-#     target_platform = "//bazel/platforms:aarch64-apple-darwin",
-# )
-
-# platform_transition_binary(
-#     name = "rust_binary_aarch64-apple-ios",
-#     binary = "//rust_binary",
-#     target_platform = "//bazel/platforms:aarch64-apple-ios",
-# )
-
-platform_transition_binary(
-    name = "rust_binary_aarch64-linux-android",
-    binary = "//rust_binary",
-    target_platform = "//bazel/platforms:aarch64-linux-android",
-)
-
-platform_transition_binary(
-    name = "rust_binary_aarch64-unknown-linux-gnu",
-    binary = "//rust_binary",
-    target_platform = "//bazel/platforms:aarch64-unknown-linux-gnu",
-)
-
-platform_transition_binary(
-    name = "rust_binary_wasm32-unknown-unknown",
-    binary = "//rust_binary",
-    target_platform = "//bazel/platforms:wasm32-unknown-unknown",
-)
-
-platform_transition_binary(
-    name = "rust_binary_wasm32-wasi",
-    binary = "//rust_binary",
-    target_platform = "//bazel/platforms:wasm32-wasi",
-)
-
-# platform_transition_binary(
-#     name = "rust_binary_x86_64-apple-darwin",
-#     binary = "//rust_binary",
-#     target_platform = "//bazel/platforms:x86_64-apple-darwin",
-# )
-
-# platform_transition_binary(
-#     name = "rust_binary_x86_64-pc-windows-msvc",
-#     binary = "//rust_binary",
-#     target_platform = "//bazel/platforms:x86_64-pc-windows-msvc",
-# )
-
-platform_transition_binary(
-    name = "rust_binary_x86_64-unknown-linux-gnu",
-    binary = "//rust_binary",
-    target_platform = "//bazel/platforms:x86_64-unknown-linux-gnu",
-)
-
-platform_transition_binary(
-    name = "rust_binary_x86_64-unknown-nixos-gnu",
-    binary = "//rust_binary",
-    target_platform = "//bazel/platforms:x86_64-unknown-nixos-gnu",
-)
diff --git a/examples/nix_cross_compiling/cc_binary/BUILD.bazel b/examples/nix_cross_compiling/cc_binary/BUILD.bazel
@@ -1,7 +1,70 @@
 load("@rules_cc//cc:defs.bzl", "cc_binary")
+load("//bazel:transitions.bzl", "platform_transition_binary")
 
 package(default_visibility = ["//visibility:public"])
 
+# Disabled targets need the user to supply a sysroot in `flake.nix` first.
+
+# platform_transition_binary(
+#     name = "cc_binary_aarch64-apple-darwin",
+#     binary = ":cc_binary",
+#     target_platform = "//bazel/platforms:aarch64-apple-darwin",
+# )
+
+# platform_transition_binary(
+#     name = "cc_binary_aarch64-apple-ios",
+#     binary = ":cc_binary",
+#     target_platform = "//bazel/platforms:aarch64-apple-ios",
+# )
+
+platform_transition_binary(
+    name = "cc_binary_aarch64-linux-android",
+    binary = ":cc_binary",
+    target_platform = "//bazel/platforms:aarch64-linux-android",
+)
+
+platform_transition_binary(
+    name = "cc_binary_aarch64-unknown-linux-gnu",
+    binary = ":cc_binary",
+    target_platform = "//bazel/platforms:aarch64-unknown-linux-gnu",
+)
+
+platform_transition_binary(
+    name = "cc_binary_wasm32-unknown-unknown",
+    binary = ":cc_binary",
+    target_platform = "//bazel/platforms:wasm32-unknown-unknown",
+)
+
+platform_transition_binary(
+    name = "cc_binary_wasm32-wasi",
+    binary = ":cc_binary",
+    target_platform = "//bazel/platforms:wasm32-wasi",
+)
+
+# platform_transition_binary(
+#     name = "cc_binary_x86_64-apple-darwin",
+#     binary = ":cc_binary",
+#     target_platform = "//bazel/platforms:x86_64-apple-darwin",
+# )
+
+# platform_transition_binary(
+#     name = "cc_binary_x86_64-pc-windows-msvc",
+#     binary = ":cc_binary",
+#     target_platform = "//bazel/platforms:x86_64-pc-windows-msvc",
+# )
+
+platform_transition_binary(
+    name = "cc_binary_x86_64-unknown-linux-gnu",
+    binary = ":cc_binary",
+    target_platform = "//bazel/platforms:x86_64-unknown-linux-gnu",
+)
+
+platform_transition_binary(
+    name = "cc_binary_x86_64-unknown-nixos-gnu",
+    binary = ":cc_binary",
+    target_platform = "//bazel/platforms:x86_64-unknown-nixos-gnu",
+)
+
 cc_binary(
     name = "cc_binary",
     srcs = select({

diff --git a/examples/nix_cross_compiling/rust_binary/BUILD.bazel b/examples/nix_cross_compiling/rust_binary/BUILD.bazel
@@ -2,27 +2,123 @@ load("@rules_rust//rust:defs.bzl", "rust_binary")
 
 package(default_visibility = ["//visibility:public"])
 
+# rust_binary(
+#     name = "rust_binary_aarch64-apple-darwin",
+#     srcs = ["rust_binary.rs"],
+#     platform = "//bazel/platforms:aarch64-apple-darwin",
+#     deps = [
+#         "//cc_library",
+#         "//rust_library",
+#         "@crate_index//:anyhow",
+#         "@crate_index//:tokio",
+#     ],
+# )
+
+# rust_binary(
+#     name = "rust_binary_aarch64-apple-ios",
+#     srcs = ["rust_binary.rs"],
+#     platform = "//bazel/platforms:aarch64-apple-ios",
+#     deps = [
+#         "//cc_library",
+#         "//rust_library",
+#         "@crate_index//:anyhow",
+#         "@crate_index//:tokio",
+#     ],
+# )
+
+rust_binary(
+    name = "rust_binary_aarch64-linux-android",
+    srcs = ["rust_binary.rs"],
+    platform = "//bazel/platforms:aarch64-linux-android",
+    deps = [
+        "//cc_library",
+        "//rust_library",
+        "@crate_index//:anyhow",
+        "@crate_index//:tokio",
+    ],
+)
+
+rust_binary(
+    name = "rust_binary_aarch64-unknown-linux-gnu",
+    srcs = ["rust_binary.rs"],
+    platform = "//bazel/platforms:aarch64-unknown-linux-gnu",
+    deps = [
+        "//cc_library",
+        "//rust_library",
+        "@crate_index//:anyhow",
+        "@crate_index//:tokio",
+    ],
+)
+
 rust_binary(
-    name = "rust_binary",
-    srcs = select({
-        # See comments in `rust_binary_wasm32-unknown-unknown.rs`.
-        "@platforms//os:none": ["rust_binary_wasm32-unknown-unknown.rs"],
-        # See comments in `rust_binary_wasm32-wasi.rs`.
-        "@platforms//os:wasi": ["rust_binary_wasm32-wasi.rs"],
-        "//conditions:default": ["rust_binary.rs"],
-    }),
-    tags = ["platform_missing"],
+    name = "rust_binary_wasm32-unknown-unknown",
+    srcs = ["rust_binary_wasm32-unknown-unknown.rs"],  # See comments in `rust_binary_wasm32-unknown-unknown.rs`.
+    platform = "//bazel/platforms:wasm32-unknown-unknown",
     deps = [
         "//cc_library",
         "//rust_library",
         "@crate_index//:anyhow",
-    ] + select({
-        "@platforms//os:none": [],
-        # To be removed once the `wasm32-wasi` version of `tokio` can `select()`
+    ],
+)
+
+rust_binary(
+    name = "rust_binary_wasm32-wasi",
+    srcs = ["rust_binary_wasm32-wasi.rs"],  # See comments in `rust_binary_wasm32-wasi.rs`.
+    platform = "//bazel/platforms:wasm32-wasi",
+    deps = [
+        "//cc_library",
+        "//rust_library",
+        "@crate_index//:anyhow",
+        # To be added once the `wasm32-wasi` version of `tokio` can `select()`
         # over different features.
-        "@platforms//os:wasi": [],
-        "//conditions:default": [
-            "@crate_index//:tokio",
-        ],
-    }),
+        # "@crate_index//:tokio",
+    ],
+)
+
+# rust_binary(
+#     name = "rust_binary_x86_64-apple-darwin",
+#     srcs = ["rust_binary.rs"],
+#     platform = "//bazel/platforms:x86_64-apple-darwin",
+#     deps = [
+#         "//cc_library",
+#         "//rust_library",
+#         "@crate_index//:anyhow",
+#         "@crate_index//:tokio",
+#     ],
+# )
+
+# rust_binary(
+#     name = "rust_binary_x86_64-pc-windows-msvc",
+#     srcs = ["rust_binary.rs"],
+#     platform = "//bazel/platforms:x86_64-pc-windows-msvc",
+#     deps = [
+#         "//cc_library",
+#         "//rust_library",
+#         "@crate_index//:anyhow",
+#         "@crate_index//:tokio",
+#     ],
+# )
+
+rust_binary(
+    name = "rust_binary_x86_64-unknown-linux-gnu",
+    srcs = ["rust_binary.rs"],
+    platform = "//bazel/platforms:x86_64-unknown-linux-gnu",
+    deps = [
+        "//cc_library",
+        "//rust_library",
+        "@crate_index//:anyhow",
+        "@crate_index//:tokio",
+    ],
+)
+
+rust_binary(
+    name = "rust_binary_x86_64-unknown-nixos-gnu",
+    srcs = ["rust_binary.rs"],
+    platform = "//bazel/platforms:x86_64-unknown-nixos-gnu",
+    deps = [
+        "//cc_library",
+        "//rust_library",
+        "@crate_index//:anyhow",
+        "@crate_index//:tokio",
+    ],
 )