Inform users that crate and srcs are mutually exclusive (#1650)

This should avoid confusion in cases where users have defined tests with
both `rust_test.crate` and `rust_test.srcs` set and later find
`rust_test.srcs` are actually unused and not being tested.

relates to #2324

examples/crate_universe/no_cargo_manifests/BUILD.bazel

@@ -19,7 +19,6 @@ rust_binary(
 
 rust_test(
     name = "unit_test",
-    srcs = glob(["**/*.rs"]),
     crate = ":no_cargo_manifests",
     edition = "2018",
 )

examples/crate_universe/vendor_local_pkgs/BUILD.bazel

@@ -69,7 +69,6 @@ rust_binary(
 
 rust_test(
     name = "unit_test",
-    srcs = glob(["**/*.rs"]),
     crate = ":vendor_local",
     edition = "2018",
 )

examples/crate_universe/vendor_remote_pkgs/BUILD.bazel

@@ -75,7 +75,6 @@ rust_binary(
 
 rust_test(
     name = "unit_test",
-    srcs = glob(["**/*.rs"]),
     crate = ":vendor_remote",
     edition = "2018",
 )

examples/crate_universe_unnamed/vendor_remote_pkgs/BUILD.bazel

@@ -70,7 +70,6 @@ rust_binary(
 
 rust_test(
     name = "unit_test",
-    srcs = glob(["**/*.rs"]),
     crate = ":vendor_remote",
     edition = "2018",
 )

rust/private/rust.bzl

@@ -283,6 +283,12 @@ def _rust_test_impl(ctx):
     deps = transform_deps(ctx.attr.deps)
     proc_macro_deps = transform_deps(ctx.attr.proc_macro_deps + get_import_macro_deps(ctx))
 
+    if toolchain._incompatible_test_attr_crate_and_srcs_mutually_exclusive:
+        if ctx.attr.crate and ctx.attr.srcs:
+            fail("rust_test.crate and rust_test.srcs are mutually exclusive. Update {} to use only one of these attributes".format(
+                ctx.label,
+            ))
+
     if ctx.attr.crate:
         # Target is building the crate in `test` config
         crate = ctx.attr.crate[rust_common.crate_info] if rust_common.crate_info in ctx.attr.crate else ctx.attr.crate[rust_common.test_crate_info].crate

rust/settings/BUILD.bazel

@@ -4,6 +4,11 @@ load(":incompatible.bzl", "incompatible_flag")
 
 package(default_visibility = ["//visibility:public"])
 
+bzl_library(
+    name = "bzl_lib",
+    srcs = glob(["**/*.bzl"]),
+)
+
 # A flag controlling whether to rename first-party crates such that their names
 # encode the Bazel package and target name, instead of just the target name.
 #
@@ -60,14 +65,16 @@ bool_flag(
     build_setting_default = False,
 )
 
-bzl_library(
-    name = "bzl_lib",
-    srcs = glob(["**/*.bzl"]),
-)
-
 # A flag to set rustc --sysroot flag to the sysroot generated by rust_toolchain
 incompatible_flag(
     name = "experimental_toolchain_generated_sysroot",
     build_setting_default = True,
     issue = "https://github.com/bazelbuild/rules_rust/issues/2039",
 )
+
+# A flag to make `rust_test.crate` and `rust_test.srcs` mutually exclusive.
+incompatible_flag(
+    name = "incompatible_test_attr_crate_and_srcs_mutually_exclusive",
+    build_setting_default = True,
+    issue = "https://github.com/bazelbuild/rules_rust/issues/2324",
+)

rust/toolchain.bzl

@@ -643,6 +643,7 @@ def _rust_toolchain_impl(ctx):
         _experimental_use_global_allocator = experimental_use_global_allocator,
         _experimental_use_coverage_metadata_files = ctx.attr._experimental_use_coverage_metadata_files[BuildSettingInfo].value,
         _experimental_toolchain_generated_sysroot = ctx.attr._experimental_toolchain_generated_sysroot[IncompatibleFlagInfo].enabled,
+        _incompatible_test_attr_crate_and_srcs_mutually_exclusive = ctx.attr._incompatible_test_attr_crate_and_srcs_mutually_exclusive[IncompatibleFlagInfo].enabled,
         _no_std = no_std,
     )
     return [
@@ -806,6 +807,9 @@ rust_toolchain = rule(
                 "This flag is only relevant when used together with --@rules_rust//rust/settings:experimental_use_global_allocator."
             ),
         ),
+        "_incompatible_test_attr_crate_and_srcs_mutually_exclusive": attr.label(
+            default = Label("//rust/settings:incompatible_test_attr_crate_and_srcs_mutually_exclusive"),
+        ),
         "_no_std": attr.label(
             default = Label("//:no_std"),
         ),

test/out_dir_in_tests/BUILD.bazel

@@ -30,9 +30,6 @@ rust_doc_test(
 rust_test_suite(
     name = "suite",
     srcs = glob(["tests/**"]),
-    # Add the 'crate' argument, which will be passed as a kwarg
-    # to the underlying rust_test rules. This will make OUT_DIR
-    # available when compiling integration tests.
-    crate = ":demo_lib",
     edition = "2018",
+    deps = [":build_script"],
 )