Map all generated input roots into legacy doctest runfiles (#4271)

Legacy doctests run from a runfiles directory, but the launcher only
strips output roots found through crate and C++ library providers. A
generated rustc environment file built in an execution configuration
retains a `bazel-out/...` path and fails before rustdoc starts.

Collect the nonempty roots of every declared action input instead. This
also covers generated compiler/linker tools and keeps source paths
intact. The new regression executes a doctest using an environment file
forwarded through an execution transition; it fails with a missing-file
error on main and passes with this change.

Validation on macOS with Bazel 9.2.0: 17 owning tests pass on this
standalone branch. This extends the C++ runtime-root handling from
#4220. Windows execution was not tested locally.

Closes #4288.

Author: jrandolf

rust/private/rustdoc_test.bzl

@@ -20,16 +20,7 @@ load("//rust/private:providers.bzl", "CrateInfo")
 load("//rust/private:rustdoc.bzl", "rustdoc_compile_action")
 load("//rust/private:utils.bzl", "dedent", "find_toolchain", "transform_deps")
 
-def _collect_library_roots(roots, deps):
-    for dep in deps.to_list():
-        for lib in dep.libraries:
-            for artifact in [lib.static_library, lib.pic_static_library]:
-                if artifact:
-                    roots.append(artifact.root.path)
-        for input in dep.additional_inputs:
-            roots.append(input.root.path)
-
-def _construct_writer_arguments(ctx, test_runner, opt_test_params, action, crate_info):
+def _construct_writer_arguments(ctx, test_runner, opt_test_params, action):
     """Construct arguments and environment variables specific to `rustdoc_test_writer`.
 
     This is largely solving for the fact that tests run from a runfiles directory
@@ -41,7 +32,6 @@ def _construct_writer_arguments(ctx, test_runner, opt_test_params, action, crate
         test_runner (File): The test_runner output file declared by `rustdoc_test`.
         opt_test_params (File): An output file we can optionally use to store params for `rustdoc`.
         action (struct): Action arguments generated by `rustdoc_compile_action`.
-        crate_info (CrateInfo): The provider of the crate who's docs are being tested.
 
     Returns:
         tuple: A tuple of `rustdoc_test_writer` specific inputs
@@ -65,46 +55,11 @@ def _construct_writer_arguments(ctx, test_runner, opt_test_params, action, crate
     for var in action.env.keys():
         writer_args.add("--action_env={}".format(var))
 
-    # Since the test runner will be running from a runfiles directory, the
-    # paths originally generated for the build action will not map to any
-    # files. To ensure rustdoc can find the appropriate dependencies, the
-    # file roots are identified and tracked for each dependency so it can be
-    # stripped from the test runner.
-
-    # Collect and dedupe all of the file roots in a list before appending
-    # them to args to prevent generating a large amount of identical args
-    roots = [crate_info.output.root.path]
-    for dep in crate_info.deps.to_list() + crate_info.proc_macro_deps.to_list():
-        dep_crate_info = getattr(dep, "crate_info", None)
-        dep_dep_info = getattr(dep, "dep_info", None)
-        dep_cc_info = getattr(dep, "cc_info", None)
-        if dep_crate_info:
-            roots.append(dep_crate_info.output.root.path)
-        if dep_dep_info:
-            for direct_dep in dep_dep_info.direct_crates.to_list():
-                roots.append(direct_dep.dep.output.root.path)
-            for transitive_dep in dep_dep_info.transitive_crates.to_list():
-                roots.append(transitive_dep.output.root.path)
-            _collect_library_roots(roots, dep_dep_info.transitive_noncrates)
-        if dep_cc_info:
-            _collect_library_roots(roots, dep_cc_info.linking_context.linker_inputs)
-
-    # The cc_toolchain runtime libs (see rustdoc.bzl) are built in their own
-    # configuration, so their root differs from every crate root collected
-    # above. Without stripping it too, the `-Lnative=` search path rustc emits
-    # for them stays an execroot path that does not exist under runfiles, and
-    # the linker reports "unable to find library".
-    #
-    # Source files have an empty root, and they need no stripping: their
-    # `-Lnative=` path is already workspace-relative. Skip them -- an empty
-    # root would add `--strip_substring=/`, and the writer applies these as
-    # plain string replacements, so that would delete every `/` in every
-    # argument.
-    for lib in action.static_runtime_libs:
-        if lib.root.path:
-            roots.append(lib.root.path)
-
-    writer_args.add_all(roots, format_each = "--strip_substring=%s/", uniquify = True)
+    # Every declared input is staged in runfiles. Strip each generated root,
+    # including compiler tools built in an execution configuration. Empty roots
+    # are source files: stripping "/" would corrupt every path in the command.
+    roots = {file.root.path: True for file in action.inputs.to_list() if file.root.path}
+    writer_args.add_all(roots.keys(), format_each = "--strip_substring=%s/")
 
     # Indicate that the rustdoc_test args are over.
     writer_args.add("--")
@@ -287,7 +242,6 @@ def _legacy_rust_doc_test_impl(ctx, toolchain, crate_info):
         test_runner = test_runner,
         opt_test_params = opt_test_params,
         action = action,
-        crate_info = crate_info,
     )
 
     # Allow writer environment variables to override those from the action.

test/rustdoc_generated_inputs/BUILD.bazel

@@ -0,0 +1,31 @@
+load("@bazel_skylib//rules:write_file.bzl", "write_file")
+load("//rust:defs.bzl", "rust_doc_test", "rust_library")
+load(":input.bzl", "exec_file")
+
+rust_doc_test(
+    name = "generated_environment_test",
+    crate = ":lib",
+    # Legacy doctests require directory runfiles on Windows (#1156).
+    target_compatible_with = select({
+        "@platforms//os:windows": ["@platforms//:incompatible"],
+        "//conditions:default": [],
+    }),
+)
+
+rust_library(
+    name = "lib",
+    srcs = ["lib.rs"],
+    edition = "2021",
+    rustc_env_files = [":exec_environment"],
+)
+
+exec_file(
+    name = "exec_environment",
+    src = ":environment",
+)
+
+write_file(
+    name = "environment",
+    out = "environment.txt",
+    content = ["GENERATED_VALUE=from the execution configuration"],
+)

test/rustdoc_generated_inputs/input.bzl

@@ -0,0 +1,11 @@
+"""Expose an environment file built in an execution configuration."""
+
+def _exec_file_impl(ctx):
+    return [DefaultInfo(files = ctx.attr.src[DefaultInfo].files)]
+
+exec_file = rule(
+    implementation = _exec_file_impl,
+    attrs = {
+        "src": attr.label(mandatory = True, cfg = "exec"),
+    },
+)

test/rustdoc_generated_inputs/lib.rs

@@ -0,0 +1,10 @@
+//! The wrapper must find generated environment files after moving into runfiles.
+//!
+//! Unlike the runtime libraries covered by #4220, this file has no crate or
+//! C++ dependency provider from which the legacy launcher could infer its root.
+//!
+//! ```
+//! assert_eq!(env!("GENERATED_VALUE"), "from the execution configuration");
+//! ```
+
+#![warn(rust_2018_idioms)]