Better handling of self-edges

Author: dzbarsky

README.md

@@ -134,6 +134,17 @@ use_repo(crate, "crates")
 
 `crate.spec` and vendoring mode are currently unsupported.
 
+### Self dev-dependencies
+
+Cargo workspaces sometimes use a self-referencing dev-dependency to enable extra features for tests:
+
+```toml
+[dev-dependencies]
+mycrate = { path = ".", features = ["test-utils"] }
+```
+
+`rules_rs` suppresses the generated self-edge in `aliases()` and `all_crate_deps()` so this pattern does not create a Bazel dependency cycle. The requested features are still part of the workspace feature resolution, so they may be enabled on the first-party crate more broadly than Cargo would enable them for a single targeted test command. If you need separate normal and test feature variants, model them as separate Bazel targets, with the test-only variant setting the extra `crate_features` and `testonly = True`.
+
 ### Exec vs target triple caveats
 
 - Windows: the default Windows **exec** toolchain is MSVC-flavored. The upstream `gnullvm` toolchain dynamically links `libunwind`, which may not exist on a stock Windows machine.

rs/extensions.bzl

@@ -1012,6 +1012,7 @@ RESOLVED_PLATFORMS = select({{
         build_deps = {triple: set() for triple in platform_triples}
         dev_deps = {triple: set() for triple in platform_triples}
         package_dir = _manifest_package_dir(package["manifest_path"], repo_root)
+        package_manifest_dir = _normalize_path(package["manifest_path"]).removesuffix("/Cargo.toml")
         binaries = {}
         shared_libraries = {}
         feature_resolutions = feature_resolutions_by_fq_crate.get(_fq_crate(package["name"], package["version"]))
@@ -1036,18 +1037,21 @@ RESOLVED_PLATFORMS = select({{
 
         for dep in package["dependencies"]:
             bazel_target = dep.get("bazel_target")
+            dep_path = dep.get("path")
             if not bazel_target:
-                dep_path = dep.get("path")
                 if not dep_path:
                     # Git or registry deps without a bazel_target are resolved
                     # elsewhere (e.g., as external crate repos). Skip here.
                     continue
                 bazel_target = "//" + paths.join(workspace_package, _normalize_path(dep_path).removeprefix(repo_root + "/"))
 
-            if dep.get("rename"):
-                aliases[bazel_target] = dep["rename"].replace("-", "_")
-            elif dep.get("path"):
-                aliases[bazel_target] = dep["name"].replace("-", "_")
+            is_self_dep = dep_path and _normalize_path(dep_path) == package_manifest_dir
+
+            if not is_self_dep:
+                if dep.get("rename"):
+                    aliases[bazel_target] = dep["rename"].replace("-", "_")
+                elif dep_path:
+                    aliases[bazel_target] = dep["name"].replace("-", "_")
 
             target = dep.get("target")
             match_info = _cfg_match_info_for_target(target, platform_cfg_attrs, cfg_match_cache)
@@ -1068,6 +1072,9 @@ RESOLVED_PLATFORMS = select({{
                     if dep_name not in triple_features and ("dep:" + dep_name) not in triple_features:
                         continue
 
+                if is_self_dep:
+                    continue
+
                 target_deps[triple].add(bazel_target)
 
         if feature_resolutions:

test/BUILD.bazel

@@ -2,11 +2,13 @@ load("@bazel_lib//lib:transitions.bzl", "platform_transition_filegroup")
 load("@build_script_aliases//:data.bzl", build_script_aliases_dep_data = "DEP_DATA")
 load("@rules_rs//rs:rust_binary.bzl", "rust_binary")
 load("@rules_shell//shell:sh_test.bzl", "sh_test")
+load("@self_dev_dependency//:data.bzl", self_dev_dependency_dep_data = "DEP_DATA")
+load("@self_dev_dependency//:defs.bzl", self_dev_dependency_aliases = "aliases")
 load("@target_workspace_dep_feature//:data.bzl", target_workspace_dep_feature_dep_data = "DEP_DATA")
 load("@workspace_default_features//:data.bzl", workspace_default_features_dep_data = "DEP_DATA")
 load("@workspace_hyphen_dep_aliases//:defs.bzl", workspace_hyphen_dep_aliases_aliases = "aliases")
 load("@workspace_renamed_path_dep_aliases//:defs.bzl", workspace_renamed_path_dep_aliases_aliases = "aliases")
-load("//:verify_aliases.bzl", "verify_alias", "verify_crate_feature_absent", "verify_crate_feature_present", "verify_dep_absent", "verify_dep_present")
+load("//:verify_aliases.bzl", "verify_alias", "verify_alias_absent", "verify_crate_feature_absent", "verify_crate_feature_present", "verify_dep_absent", "verify_dep_present", "verify_dev_dep_absent")
 
 sh_test(
     name = "dummy_test",
@@ -146,6 +148,24 @@ verify_alias(
     expected_label = "//workspace_renamed_path_dep_aliases/dep-crate",
 )
 
+verify_alias_absent(
+    name = "verify_self_dev_dependency_no_self_alias",
+    aliases = self_dev_dependency_aliases(package_name = "self_dev_dependency/mycrate"),
+    unexpected_label = "//self_dev_dependency/mycrate",
+)
+
+verify_dev_dep_absent(
+    name = "verify_self_dev_dependency_no_self_dev_dep",
+    dep_data = self_dev_dependency_dep_data["self_dev_dependency/mycrate"],
+    unexpected = "//self_dev_dependency/mycrate",
+)
+
+verify_crate_feature_present(
+    name = "verify_self_dev_dependency_feature_present",
+    dep_data = self_dev_dependency_dep_data["self_dev_dependency/mycrate"],
+    expected = "test-utils",
+)
+
 verify_dep_present(
     name = "verify_single_crate_dep_data_key",
     dep_data = build_script_aliases_dep_data["build_script_aliases"],
@@ -229,6 +249,9 @@ filegroup(
         ":verify_cfg_feature_target_dep",
         ":verify_first_party_feature_propagation",
         ":verify_rust_analyzer_toolchain",
+        ":verify_self_dev_dependency_feature_present",
+        ":verify_self_dev_dependency_no_self_alias",
+        ":verify_self_dev_dependency_no_self_dev_dep",
         ":verify_single_crate_dep_data_key",
         ":verify_target_workspace_dep_feature_dep_absent",
         ":verify_target_workspace_dep_feature_feature_absent",
@@ -239,6 +262,7 @@ filegroup(
         ":verify_workspace_member_annotation_features",
         ":verify_workspace_renamed_path_dep_aliases",
         "//prost:echo_rust_proto",
+        "//self_dev_dependency/mycrate",
         "@binaries//:protoc-gen-prost-extra",
         "@binaries//:protoc-gen-prost__protoc-gen-prost",
     ] + select({

test/MODULE.bazel

@@ -144,6 +144,7 @@ TESTS = [
     "non_optional_dep_feature",
     "optional_build_deps",
     "platform_dep_features",
+    "self_dev_dependency",
     "target_workspace_dep_feature",
     "vendored_crate_override",
     "workspace_default_features",

test/self_dev_dependency/Cargo.lock

@@ -0,0 +1,3 @@
+[workspace]
+resolver = "2"
+members = ["mycrate"]

test/self_dev_dependency/Cargo.toml

@@ -0,0 +1,10 @@
+load("@rules_rs//rs:rust_library.bzl", "rust_library")
+load("@self_dev_dependency//:defs.bzl", "aliases", "all_crate_deps")
+
+rust_library(
+    name = "mycrate",
+    srcs = glob(["src/**/*.rs"]),
+    aliases = aliases(),
+    crate_name = "mycrate",
+    deps = all_crate_deps(normal = True),
+)

test/self_dev_dependency/mycrate/BUILD.bazel

@@ -0,0 +1,10 @@
+[package]
+name = "mycrate"
+version = "0.1.0"
+edition = "2021"
+
+[features]
+test-utils = []
+
+[dev-dependencies]
+mycrate = { path = ".", features = ["test-utils"] }

test/self_dev_dependency/mycrate/Cargo.toml

@@ -0,0 +1,2 @@
+#[cfg(feature = "test-utils")]
+pub fn test_helper() {}

test/self_dev_dependency/mycrate/src/lib.rs

@@ -23,6 +23,13 @@ verify_alias = rule(
     },
 )
 
+def verify_alias_absent(name, aliases, unexpected_label):
+    _verify_absent(
+        name = name,
+        items = sorted(aliases.keys()),
+        unexpected = unexpected_label,
+    )
+
 def _verify_absent_impl(ctx):
     if ctx.attr.unexpected in ctx.attr.items:
         fail("Did not expect %r in %r" % (ctx.attr.unexpected, ctx.attr.items))
@@ -66,6 +73,17 @@ def verify_dep_absent(name, dep_data, unexpected):
         unexpected = unexpected,
     )
 
+def verify_dev_dep_absent(name, dep_data, unexpected):
+    items = list(dep_data.get("dev_deps", []))
+    for values in dep_data.get("dev_deps_by_platform", {}).values():
+        items.extend(values)
+
+    _verify_absent(
+        name = name,
+        items = sorted(items),
+        unexpected = unexpected,
+    )
+
 def verify_dep_present(name, dep_data, expected):
     items = list(dep_data.get("deps", []))
     for values in dep_data.get("deps_by_platform", {}).values():