Add support for override_target when using bzlmod

.bazelci/presubmit.yml

@@ -717,6 +717,14 @@ tasks:
     working_directory: examples/bzlmod/hello_world_no_cargo
     build_targets:
       - "//..."
+  bzlmod_override_targets:
+    name: Override Targets bzlmod
+    platform: ubuntu2004
+    working_directory: examples/bzlmod/override_target
+    build_targets:
+      - "//..."
+    test_targets:
+      - "//..."
   compile_one_dependency:
     name: --compile_one_dependency flag
     platform: ubuntu2004

crate_universe/extension.bzl

@@ -296,6 +296,31 @@ def _crate_impl(module_ctx):
             if annotation_dict.pop("gen_all_binaries"):
                 annotation_dict["gen_binaries"] = True
             annotation_dict["gen_build_script"] = _OPT_BOOL_VALUES[annotation_dict["gen_build_script"]]
+
+            # Process the override targets for the annotation.
+            # In the non-bzlmod approach, this is given as a dict
+            # with the possible keys "`proc_macro`, `build_script`, `lib`, `bin`".
+            # With the tag-based approach used in Bzlmod, we run into an issue
+            # where there is no dict type that takes a string as a key and a Label as the value.
+            # To work around this, we split the override option into four, and reconstruct the
+            # dictionary here during processing
+            annotation_dict["override_targets"] = dict()
+            replacement = annotation_dict.pop("override_target_lib")
+            if replacement:
+                annotation_dict["override_targets"]["lib"] = str(replacement)
+
+            replacement = annotation_dict.pop("override_target_proc_macro")
+            if replacement:
+                annotation_dict["override_targets"]["proc_macro"] = str(replacement)
+
+            replacement = annotation_dict.pop("override_target_build_script")
+            if replacement:
+                annotation_dict["override_targets"]["build_script"] = str(replacement)
+
+            replacement = annotation_dict.pop("override_target_bin")
+            if replacement:
+                annotation_dict["override_targets"]["bin"] = str(replacement)
+
             annotation = _crate_universe_crate.annotation(**{
                 k: v
                 for k, v in annotation_dict.items()
@@ -483,6 +508,18 @@ _annotation = tag_class(
         shallow_since = attr.string(
             doc = "An optional timestamp used for crates originating from a git repository instead of a crate registry. This flag optimizes fetching the source code.",
         ),
+        override_target_lib = attr.label(
+            doc = "An optional alternate taget to use when something depends on this crate to allow the parent repo to provide its own version of this dependency.",
+        ),
+        override_target_proc_macro = attr.label(
+            doc = "An optional alternate taget to use when something depends on this crate to allow the parent repo to provide its own version of this dependency.",
+        ),
+        override_target_build_script = attr.label(
+            doc = "An optional alternate taget to use when something depends on this crate to allow the parent repo to provide its own version of this dependency.",
+        ),
+        override_target_bin = attr.label(
+            doc = "An optional alternate taget to use when something depends on this crate to allow the parent repo to provide its own version of this dependency.",
+        ),
     ),
 )
 

examples/bzlmod/override_target/.bazelrc

@@ -0,0 +1,12 @@
+# Required on windows
+common --enable_platform_specific_config
+startup --windows_enable_symlinks
+build:windows --enable_runfiles
+
+build --experimental_enable_bzlmod
+
+# This isn't currently the defaut in Bazel, but we enable it to test we'll be ready if/when it flips.
+build --incompatible_disallow_empty_glob
+
+# Required for cargo_build_script support before Bazel 7
+build --incompatible_merge_fixed_and_default_shell_env

examples/bzlmod/override_target/.gitignore

@@ -0,0 +1 @@
+/bazel-*

examples/bzlmod/override_target/BUILD.bazel

@@ -0,0 +1,23 @@
+load("@rules_rust//rust:defs.bzl", "rust_library", "rust_test")
+
+rust_library(
+    name = "override_targets_example",
+    srcs = glob(["src/*.rs"]),
+    edition = "2018",
+    deps = [
+        "@override_test//:foo",
+    ],
+)
+
+rust_library(
+    name = "foo",
+    srcs = ["foo.rs"],
+    edition = "2018",
+    visibility = ["//visibility:public"],
+)
+
+rust_test(
+    name = "unit_test",
+    crate = ":override_targets_example",
+    edition = "2018",
+)

examples/bzlmod/override_target/Cargo.toml

@@ -0,0 +1,12 @@
+[workspace]
+[package]
+name = "override_targets"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[lib]
+path = "/dev/null"
+
+[dependencies.foo]
+version = "0.0.0"

examples/bzlmod/override_target/MODULE.bazel

@@ -0,0 +1,44 @@
+"""bazelbuild/rules_rust - bzlmod example"""
+
+module(
+    name = "override_target_example_with_bzlmod",
+    version = "0.0.0",
+)
+
+bazel_dep(name = "platforms", version = "0.0.8")
+bazel_dep(
+    name = "bazel_skylib",
+    version = "1.5.0",
+)
+bazel_dep(
+    name = "rules_rust",
+    version = "0.0.0",
+)
+local_path_override(
+    module_name = "rules_rust",
+    path = "../../..",
+)
+
+rust = use_extension("@rules_rust//rust:extensions.bzl", "rust")
+rust.toolchain(edition = "2021")
+use_repo(
+    rust,
+    "rust_toolchains",
+)
+
+register_toolchains("@rust_toolchains//:all")
+
+crate = use_extension(
+    "@rules_rust//crate_universe:extension.bzl",
+    "crate",
+)
+crate.from_cargo(
+    name = "override_test",
+    cargo_lockfile = "//:Cargo.lock",
+    manifests = ["//:Cargo.toml"],
+)
+crate.annotation(
+    crate = "foo",
+    override_target_lib = "@//:foo",
+)
+use_repo(crate, "override_test")

examples/bzlmod/override_target/WORKSPACE.bazel

@@ -0,0 +1 @@
+# Intentionally blank; using bzlmod

examples/bzlmod/override_target/WORKSPACE.bzlmod

@@ -0,0 +1 @@
+# Intentionally blank; enable strict mode for bzlmod

examples/bzlmod/override_target/foo.rs

@@ -0,0 +1 @@
+pub const THE_ANSWER: u32 = 42;

examples/bzlmod/override_target/src/lib.rs

@@ -0,0 +1,6 @@
+mod test {
+    #[test]
+    pub fn test() {
+        assert_eq!(foo::THE_ANSWER, 42);
+    }
+}