Handle external packages using CARGO_MANIFEST_DIR

.bazelignore

@@ -1,2 +1,3 @@
 docs
 examples
+examples/hello_cargo_manifest_dir

.gitignore

@@ -6,6 +6,7 @@
 # bazel
 /bazel-*
 /examples/bazel-*
+/examples/*/bazel-*
 /docs/bazel-*
 
 # rustfmt

WORKSPACE

@@ -59,7 +59,7 @@ examples_deps()
 
 load("@examples//:examples_transitive_deps.bzl", examples_transitive_deps = "transitive_deps")
 
-examples_transitive_deps()
+examples_transitive_deps(is_top_level = True)
 
 # Load all dependencies for docs
 

examples/.bazelignore

@@ -0,0 +1 @@
+hello_cargo_manifest_dir

examples/examples_transitive_deps.bzl

@@ -4,14 +4,35 @@ There are some transitive dependencies of the dependencies of the examples'
 dependencies. This file contains the required macros to pull these dependencies
 """
 
+load("@bazel_tools//tools/build_defs/repo:utils.bzl", "maybe")
 load("@io_bazel_rules_rust//:workspace.bzl", "rust_workspace")
 load("@rules_proto//proto:repositories.bzl", "rules_proto_dependencies", "rules_proto_toolchains")
 
-def transitive_deps():
-    """Define transitive dependencies for `rules_rust` examples"""
+# buildifier: disable=unnamed-macro
+def transitive_deps(is_top_level = False):
+    """Define transitive dependencies for `rules_rust` examples
+
+    Args:
+        is_top_level (bool, optional): Indicates wheather or not this is being called
+            from the root WORKSPACE file of `rules_rust`. Defaults to False.
+    """
 
     rules_proto_dependencies()
 
     rules_proto_toolchains()
 
     rust_workspace()
+
+    # Needed by the hello_uses_cargo_manifest_dir example.
+    if is_top_level:
+        maybe(
+            native.local_repository,
+            name = "hello_cargo_manifest_dir",
+            path = "examples/hello_cargo_manifest_dir",
+        )
+    else:
+        maybe(
+            native.local_repository,
+            name = "hello_cargo_manifest_dir",
+            path = "hello_cargo_manifest_dir",
+        )

examples/hello_cargo_manifest_dir/BUILD

@@ -0,0 +1,8 @@
+load("@io_bazel_rules_rust//rust:rust.bzl", "rust_library")
+
+rust_library(
+    name = "hello_cargo_manifest_dir",
+    srcs = ["src/lib.rs"],
+    data = ["include/included_file.rs.inc"],
+    visibility = ["//visibility:public"],
+)

examples/hello_cargo_manifest_dir/WORKSPACE

@@ -0,0 +1,12 @@
+local_repository(
+    name = "io_bazel_rules_rust",
+    path = "../..",
+)
+
+load("@io_bazel_rules_rust//rust:repositories.bzl", "rust_repositories")
+
+rust_repositories()
+
+load("@io_bazel_rules_rust//:workspace.bzl", "rust_workspace")
+
+rust_workspace()

examples/hello_cargo_manifest_dir/include/included_file.rs.inc

@@ -0,0 +1 @@
+I love veggies!

examples/hello_cargo_manifest_dir/src/lib.rs

@@ -0,0 +1,4 @@
+
+pub fn get_included_str() -> &'static str {
+    include_str!(concat!(env!("CARGO_MANIFEST_DIR"), "/include/included_file.rs.inc"))
+}

examples/hello_uses_cargo_manifest_dir/BUILD

@@ -0,0 +1,8 @@
+load("@io_bazel_rules_rust//rust:rust.bzl", "rust_test")
+
+rust_test(
+    name = "hello_uses_cargo_manifest_dir",
+    srcs = ["src/lib.rs"],
+    edition = "2018",
+    deps = ["@hello_cargo_manifest_dir"],
+)

examples/hello_uses_cargo_manifest_dir/src/lib.rs

@@ -0,0 +1,7 @@
+
+use hello_cargo_manifest_dir::get_included_str;
+
+#[test]
+fn test_lib_with_include() {
+    assert_eq!(get_included_str(), "I love veggies!\n")
+}

rust/private/rustc.bzl

@@ -442,9 +442,18 @@ def construct_arguments(
     # may not follow the `src/lib.rs` convention. As such we use `ctx.build_file_path` mapped into the
     # `exec_root`. Since we cannot (seemingly) get the `exec_root` from starlark, we cheat a little
     # and use `${pwd}` which resolves the `exec_root` at action execution time.
+    #
+    # Unfortunately, ctx.build_file_path isn't relative to the exec_root for external repositories in
+    # which case we use ctx.label.workspace_root to complete the path.
     args.add("--subst", "pwd=${pwd}")
 
-    env["CARGO_MANIFEST_DIR"] = "${pwd}/" + ctx.build_file_path[:ctx.build_file_path.rfind("/")]
+    workspace_root_items = ctx.label.workspace_root.split("/")
+    if (len(workspace_root_items) >= 2 and
+        workspace_root_items[0] == "external" and
+        workspace_root_items[-1] == ctx.build_file_path.split("/")[0]):
+        workspace_root_items = workspace_root_items[:-1]
+
+    env["CARGO_MANIFEST_DIR"] = "${pwd}/" + "/".join(workspace_root_items + ctx.build_file_path.split("/")[:-1])
 
     if out_dir != None:
         env["OUT_DIR"] = "${pwd}/" + out_dir