Update cargo_build_script to always render custom runfiles dirs.

cargo/cargo_build_script_runner/lib.rs

@@ -124,7 +124,9 @@ impl BuildScriptOutput {
     pub fn outputs_from_command(
         cmd: &mut Command,
     ) -> Result<(Vec<BuildScriptOutput>, Output), Output> {
-        let child_output = cmd.output().expect("Unable to start binary");
+        let child_output = cmd
+            .output()
+            .unwrap_or_else(|e| panic!("Unable to start command:\n{:#?}\n{:?}", cmd, e));
         if child_output.status.success() {
             let reader = BufReader::new(child_output.stdout.as_slice());
             let output = Self::outputs_from_reader(reader);

cargo/private/BUILD.bazel

@@ -1,13 +1,7 @@
 load("@bazel_skylib//:bzl_library.bzl", "bzl_library")
-load(":runfiles_enabled.bzl", "runfiles_enabled_build_setting")
 
 bzl_library(
     name = "bzl_lib",
     srcs = glob(["**/*.bzl"]),
     visibility = ["//:__subpackages__"],
 )
-
-runfiles_enabled_build_setting(
-    name = "runfiles_enabled",
-    visibility = ["//visibility:public"],
-)

cargo/private/cargo_build_script.bzl

@@ -23,7 +23,6 @@ load(
     "find_toolchain",
     _name_to_crate_name = "name_to_crate_name",
 )
-load(":runfiles_enabled.bzl", "is_runfiles_enabled", "runfiles_enabled_attr")
 
 # Reexport for cargo_build_script_wrapper.bzl
 name_to_crate_name = _name_to_crate_name
@@ -206,6 +205,23 @@ def _rlocationpath(file, workspace_name):
     return "{}/{}".format(workspace_name, file.short_path)
 
 def _create_runfiles_dir(ctx, script):
+    """Create a runfiles directory to represent `CARGO_MANIFEST_DIR`.
+
+    Due to the inability to forcibly generate runfiles directories for use as inputs
+    to actions, this function creates a custom runfiles directory that can more
+    consistently be relied upon as an input. For more details see:
+    https://github.com/bazelbuild/bazel/issues/15486
+
+    If runfiles directories can ever be more directly treated as an input this function
+    can be retired.
+
+    Args:
+        ctx (ctx): The rule's context object
+        script (Target): The `cargo_build_script.script` target.
+
+    Returns:
+        File: The directory created
+    """
     runfiles_dir = ctx.actions.declare_directory("{}.cargo_runfiles".format(ctx.label.name))
 
     # External repos always fall into the `../` branch of `_rlocationpath`.
@@ -264,13 +280,18 @@ def _cargo_build_script_impl(ctx):
     if not workspace_name:
         workspace_name = ctx.workspace_name
 
-    if not is_runfiles_enabled(ctx.attr):
+    # Relying on runfiles directories is unreliable when passing data to
+    # dependent actions. Instead, an explicit directory should be created
+    # until more reliable functionality is implemented in Bazel:
+    # https://github.com/bazelbuild/bazel/issues/15486
+    incompatible_runfiles_cargo_manifest_dir = ctx.attr._incompatible_runfiles_cargo_manifest_dir[BuildSettingInfo].value
+    if incompatible_runfiles_cargo_manifest_dir:
+        script_data.append(ctx.attr.script[DefaultInfo].default_runfiles.files)
+        manifest_dir = "{}.runfiles/{}/{}".format(script.path, workspace_name, ctx.label.package)
+    else:
         runfiles_dir = _create_runfiles_dir(ctx, ctx.attr.script)
         script_data.append(depset([runfiles_dir]))
         manifest_dir = "{}/{}/{}".format(runfiles_dir.path, workspace_name, ctx.label.package)
-    else:
-        script_data.append(ctx.attr.script[DefaultInfo].default_runfiles.files)
-        manifest_dir = "{}.runfiles/{}/{}".format(script.path, workspace_name, ctx.label.package)
 
     streams = struct(
         stdout = ctx.actions.declare_file(ctx.label.name + ".stdout.log"),
@@ -564,14 +585,15 @@ cargo_build_script = rule(
         "_experimental_symlink_execroot": attr.label(
             default = Label("//cargo/settings:experimental_symlink_execroot"),
         ),
+        "_incompatible_runfiles_cargo_manifest_dir": attr.label(
+            default = Label("//cargo/settings:incompatible_runfiles_cargo_manifest_dir"),
+        ),
         "_runfiles_maker": attr.label(
             cfg = "exec",
             executable = True,
             default = Label("//cargo/private/runfiles_maker"),
         ),
-    } | runfiles_enabled_attr(
-        default = Label("//cargo/private:runfiles_enabled"),
-    ),
+    },
     fragments = ["cpp"],
     toolchains = [
         str(Label("//rust:toolchain_type")),

cargo/private/runfiles_maker/runfiles_maker.rs

@@ -61,7 +61,7 @@ fn main() {
         .expect("Failed to create output directory");
         std::fs::copy(src, &out_dest).unwrap_or_else(|e| {
             panic!(
-                "Failed to copy file {} -> {}\n{:?}",
+                "Failed to copy file `{} -> {}`\n{:?}",
                 src.display(),
                 out_dest.display(),
                 e

cargo/settings/BUILD.bazel

@@ -8,3 +8,12 @@ bool_flag(
     name = "experimental_symlink_execroot",
     build_setting_default = False,
 )
+
+# A flag which causes `cargo_build_script` to write an explicit `CARGO_MANFIEST_DIR`
+# directory from an action instead of using runfiles directories which cannot be
+# passed to downstream actions.
+# https://github.com/bazelbuild/bazel/issues/15486
+bool_flag(
+    name = "incompatible_runfiles_cargo_manifest_dir",
+    build_setting_default = False,
+)