Fix binary-only crates (#132)

Author: isaacparker0

rs/private/git_cargo_workspace_repository.bzl

@@ -39,6 +39,7 @@ crate(
     links = {links},
     build_script = {build_script},
     is_proc_macro = {is_proc_macro},
+    has_lib = {has_lib},
     binaries = {binaries},
     package_metadata_bazel_deps = [
         {package_metadata_bazel_deps}
@@ -52,6 +53,7 @@ crate(
         links = cargo.values["links"],
         build_script = cargo.values["build_script"],
         is_proc_macro = cargo.values["is_proc_macro"],
+        has_lib = cargo.values["has_lib"],
         binaries = cargo.values["binaries"],
         package_metadata_bazel_deps = _render_label_list(cargo.bazel_metadata.get("deps", [])),
         additive_build_file_content = additive_build_file_content,

rs/private/git_crate_metadata_repository.bzl

@@ -12,6 +12,7 @@ def crate(
         links,
         build_script,
         is_proc_macro,
+        has_lib,
         binaries,
         package_metadata_bazel_deps):
 {rust_crate_call}""".format(
@@ -27,6 +28,7 @@ def crate(
                 crate_name = "crate_name",
                 crate_root = "crate_root",
                 edition = "edition",
+                has_lib = "has_lib",
                 is_proc_macro = "is_proc_macro",
                 links = "links",
                 name = repr(rctx.attr.package_name),

rs/private/repository_utils.bzl

@@ -117,6 +117,7 @@ def cargo_build_file_values(rctx, cargo_toml, gen_binaries, package_path = "", g
     lib = cargo_toml.get("lib", {})
     is_proc_macro = lib.get("proc-macro") or lib.get("proc_macro") or False
     crate_root = (lib.get("path") or "src/lib.rs").removeprefix("./")
+    has_lib = "lib" in cargo_toml or package_dir.get_child(crate_root).exists
 
     edition = package.get("edition", "2015")
     crate_name = lib.get("name")
@@ -148,6 +149,7 @@ def cargo_build_file_values(rctx, cargo_toml, gen_binaries, package_path = "", g
             "crate_name": repr(crate_name),
             "crate_root": repr(crate_root),
             "edition": repr(edition),
+            "has_lib": repr(has_lib),
             "is_proc_macro": repr(is_proc_macro),
             "links": repr(links),
         },
@@ -186,6 +188,7 @@ _RUST_CRATE_MACRO_CALL = """{indent}rust_crate(
 {indent}    build_script_tools = {build_script_tools}{conditional_build_script_tools},
 {indent}    build_script_tags = {build_script_tags},
 {indent}    is_proc_macro = {is_proc_macro},
+{indent}    has_lib = {has_lib},
 {indent}    binaries = {binaries},
 {indent}    use_legacy_rules_rust_platforms = {use_legacy_rules_rust_platforms},
 {skip_deps_verification_attr}{indent})
@@ -257,6 +260,7 @@ def render_rust_crate_call(attr, values, bazel_metadata = {}, extra_deps = "", i
         conditional_build_script_tools = " + " + conditional_build_script_tools if conditional_build_script_tools else "",
         build_script_tags = repr(attr.build_script_tags),
         is_proc_macro = values["is_proc_macro"],
+        has_lib = values["has_lib"],
         binaries = values["binaries"],
         use_legacy_rules_rust_platforms = use_legacy_rules_rust_platforms,
         skip_deps_verification_attr = skip_deps_verification_attr,

rs/rust_crate.bzl

@@ -39,6 +39,7 @@ def rust_crate(
         build_script_tools,
         build_script_tags,
         is_proc_macro,
+        has_lib,
         binaries,
         use_legacy_rules_rust_platforms,
         extra_compile_data = [],
@@ -139,43 +140,68 @@ def rust_crate(
 
     deps = deps + maybe_build_script
 
-    kwargs = dict(
-        name = name,
-        crate_name = crate_name,
-        version = version,
-        srcs = srcs,
-        compile_data = compile_data,
-        aliases = aliases,
-        deps = deps,
-        data = data,
-        crate_features = crate_features + select(
-            {_platform(k, use_legacy_rules_rust_platforms): v for k, v in conditional_crate_features.items()} |
-            {"//conditions:default": []},
-        ),
-        crate_root = crate_root,
-        edition = edition,
-        rustc_env = rustc_env,
-        rustc_env_files = ["cargo_toml_env_vars.env"],
-        rustc_flags = rustc_flags + ["--cap-lints=allow"],
-        tags = crate_tags,
-        target_compatible_with = target_compatible_with,
-        package_metadata = [name + "_package_metadata"],
-        skip_deps_verification = skip_deps_verification,
-        visibility = ["//visibility:public"],
-        skip_per_crate_rustc_flags = True,
-    )
+    if not has_lib:
+        # HACK: create a stub target so the hub's `<crate>-<version>` alias
+        # (emitted unconditionally in rs/extensions.bzl) still resolves for
+        # binary-only crates. Marked as incompatible so that library use
+        # fails at analysis time. The descriptive stub name & alias make the
+        # error self-explanatory.
+        #
+        # A cleaner fix would be to make the hub skip the library alias when
+        # the crate has no library, but that is non-trivial.
+        stub_name = name + "_no_library_only_binary"
+        native.filegroup(
+            name = stub_name,
+            tags = crate_tags,
+            target_compatible_with = ["@platforms//:incompatible"],
+            visibility = ["//visibility:public"],
+        )
+        native.alias(
+            name = name,
+            actual = ":" + stub_name,
+            tags = crate_tags,
+            visibility = ["//visibility:public"],
+        )
 
-    if is_proc_macro:
-        (_rust_proc_macro if skip_deps_verification else rust_proc_macro)(**kwargs)
-    else:
-        (_rust_library if skip_deps_verification else rust_library)(**kwargs)
+    if has_lib:
+        kwargs = dict(
+            name = name,
+            crate_name = crate_name,
+            version = version,
+            srcs = srcs,
+            compile_data = compile_data,
+            aliases = aliases,
+            deps = deps,
+            data = data,
+            crate_features = crate_features + select(
+                {_platform(k, use_legacy_rules_rust_platforms): v for k, v in conditional_crate_features.items()} |
+                {"//conditions:default": []},
+            ),
+            crate_root = crate_root,
+            edition = edition,
+            rustc_env = rustc_env,
+            rustc_env_files = ["cargo_toml_env_vars.env"],
+            rustc_flags = rustc_flags + ["--cap-lints=allow"],
+            tags = crate_tags,
+            target_compatible_with = target_compatible_with,
+            package_metadata = [name + "_package_metadata"],
+            skip_deps_verification = skip_deps_verification,
+            visibility = ["//visibility:public"],
+            skip_per_crate_rustc_flags = True,
+        )
+
+        if is_proc_macro:
+            (_rust_proc_macro if skip_deps_verification else rust_proc_macro)(**kwargs)
+        else:
+            (_rust_library if skip_deps_verification else rust_library)(**kwargs)
 
+    binary_lib_dep = [name] if has_lib else []
     for binary, crate_root in binaries.items():
         rust_binary(
             name = binary + "__bin",
             compile_data = compile_data,
             aliases = aliases,
-            deps = [name] + deps,
+            deps = binary_lib_dep + deps,
             data = data,
             crate_features = crate_features,
             crate_root = crate_root,

test/BUILD.bazel

@@ -68,10 +68,14 @@ DISABLED = [
     #"uv",
 ]
 
+# Tests whose `_workspace_deps` aggregation intentionally fails analysis.
+# Their binaries are referenced explicitly in :all_builds below.
+BINARY_ONLY_TESTS = ["binary_only"]
+
 TESTS = [f for f in glob(
     ["*"],
     exclude_directories = 0,
-) if "." not in f and "bazel-" not in f and f not in DISABLED]
+) if "." not in f and "bazel-" not in f and f not in DISABLED and f not in BINARY_ONLY_TESTS]
 
 rust_binary(
     name = "rust_binary",
@@ -328,6 +332,7 @@ filegroup(
         "//self_dev_dependency/mycrate",
         "@binaries//:protoc-gen-prost-extra",
         "@binaries//:protoc-gen-prost__protoc-gen-prost",
+        "@binary_only//:b3sum__b3sum",
     ] + select({
         "@platforms//os:windows": [],
         "//conditions:default": [

test/MODULE.bazel

@@ -158,6 +158,7 @@ TESTS = [
     "workspace_hyphen_dep_aliases",
     "workspace_renamed_path_dep_aliases",
     "binaries",
+    "binary_only",
     "uv",
 ]
 
@@ -223,6 +224,13 @@ crate.annotation(
     gen_binaries = ["protoc-gen-prost"],
 )
 
+# Test gen_binaries for a binary-only crate (no [lib], no src/lib.rs).
+crate.annotation(
+    crate = "b3sum",
+    gen_binaries = ["b3sum"],
+    repositories = ["binary_only"],
+)
+
 # Fix readme inclusions
 crate.annotation(
     crate = "windows-link",