Isolate Cargo lint tests from the production helper package

cargo/private/cargo_toml_info/BUILD.bazel

@@ -1,6 +1,5 @@
 """BUILD file for cargo info helper binary."""
 
-load("@rules_python//python:defs.bzl", "py_test")
 load("//rust:defs.bzl", "rust_binary", "rust_test")
 
 rust_binary(
@@ -15,11 +14,3 @@ rust_test(
     name = "unit_test",
     crate = ":cargo_toml_info",
 )
-
-py_test(
-    name = "declared_manifests_test",
-    srcs = ["declared_manifests_test.py"],
-    args = ["$(rlocationpath :cargo_toml_info)"],
-    data = [":cargo_toml_info"],
-    deps = ["@rules_python//python/runfiles"],
-)

cargo/tests/cargo_toml_info/BUILD.bazel

@@ -0,0 +1,10 @@
+load("@rules_python//python:defs.bzl", "py_test")
+
+# Keep dev-only test rules out of the helper package loaded by downstream users.
+py_test(
+    name = "declared_manifests_test",
+    srcs = ["declared_manifests_test.py"],
+    args = ["$(rlocationpath //cargo/private/cargo_toml_info)"],
+    data = ["//cargo/private/cargo_toml_info"],
+    deps = ["@rules_python//python/runfiles"],
+)

test/integration/cargo_lints/BUILD.bazel

@@ -0,0 +1,9 @@
+load("@rules_rust//cargo:defs.bzl", "extract_cargo_lints")
+
+# Building this from a downstream module must not load rules_rust's dev dependencies.
+# Manual check from this directory: bazel build --lockfile_mode=off //:lints
+# Root-module tests cannot reproduce the pruning of dependency dev_dependencies.
+extract_cargo_lints(
+    name = "lints",
+    manifest = "Cargo.toml",
+)

test/integration/cargo_lints/Cargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "cargo-lints-consumer"
+version = "0.1.0"
+edition = "2021"
+
+[lints.rust]
+unsafe_code = "forbid"

test/integration/cargo_lints/MODULE.bazel

@@ -0,0 +1,7 @@
+module(name = "cargo_lints_consumer")
+
+bazel_dep(name = "rules_rust", version = "0.0.0")
+local_path_override(
+    module_name = "rules_rust",
+    path = "../../..",
+)