Fix cache poisoning with Swift incremental compilation

test/worker/BUILD

@@ -0,0 +1,26 @@
+load(":worker_test.bzl", "worker_test")
+
+[
+    worker_test(
+        name = name + "_test",
+        size = "medium",
+        scenario = name,
+        target_compatible_with = select({
+            "@platforms//os:windows": ["@platforms//:incompatible"],
+            "//conditions:default": [],
+        }),
+    )
+    for name in [
+        "module_outputs_survive_failure",
+        "changed_dependency_digest",
+        "changed_dependency_digest_without_hashing",
+        "changed_arguments",
+        "changed_universal_arguments",
+        "missing_digest",
+        "removed_dependency_input",
+        "missing_input_record",
+        "corrupt_input_record",
+        "atomic_input_record",
+        "failed_dependency_change",
+    ]
+]

test/worker/observe_swiftc.sh

@@ -0,0 +1,17 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+# Observe the worker's invalidation decisions before Swift updates its records.
+mkdir -p observed_dependencies
+for dependency in "$INCREMENTAL_DIR"/*.swiftdeps "$INCREMENTAL_DIR"/*.priors; do
+	if [[ -f "$dependency" ]]; then
+		cp "$dependency" observed_dependencies/
+	fi
+done
+
+# Forward Swift's response file unchanged, including its argument quoting.
+if [[ "$OSTYPE" == darwin* ]]; then
+	exec /usr/bin/xcrun "$WORKER_TEST_COMPILER" "$@"
+fi
+exec "$WORKER_TEST_COMPILER" "$@"

test/worker/worker_test.bzl

@@ -0,0 +1,71 @@
+"""Runs worker regression tests with the configured Swift compiler."""
+
+load("@bazel_skylib//lib:shell.bzl", "shell")
+
+# buildifier: disable=bzl-visibility
+load(
+    "//swift/internal:action_names.bzl",
+    "SWIFT_ACTION_AUTOLINK_EXTRACT",
+    "SWIFT_ACTION_COMPILE",
+)
+
+# buildifier: disable=bzl-visibility
+load("//swift/internal:feature_names.bzl", "SWIFT_FEATURE_INCREMENTAL_FILE_HASHING")
+
+def _worker_test_impl(ctx):
+    toolchain = ctx.toolchains["//toolchains:toolchain_type"].swift_toolchain
+    compiler = toolchain.tool_configs[SWIFT_ACTION_COMPILE]
+    files = [ctx.file._script, ctx.file._observer, ctx.executable._worker]
+    files.extend(compiler.additional_tools)
+
+    # The test also links a client, which invokes the autolink extractor on Linux.
+    autolink_extractor = toolchain.tool_configs.get(SWIFT_ACTION_AUTOLINK_EXTRACT)
+    if autolink_extractor:
+        files.extend(autolink_extractor.additional_tools)
+        if type(autolink_extractor.executable) == "File":
+            files.append(autolink_extractor.executable)
+
+    executable = compiler.executable
+    if type(executable) == "File":
+        files.append(executable)
+        executable = executable.short_path
+    elif executable.startswith("external/"):
+        executable = "../" + executable.removeprefix("external/")
+
+    runner = ctx.actions.declare_file(ctx.label.name + ".sh")
+    ctx.actions.write(
+        output = runner,
+        content = "#!/usr/bin/env bash\nexec bash {} \"$@\"\n".format(" ".join([
+            shell.quote(arg)
+            for arg in [
+                ctx.file._script.short_path,
+                ctx.executable._worker.short_path,
+                ctx.file._observer.short_path,
+                ctx.attr.scenario,
+                executable,
+            ] + compiler.args
+        ])),
+        is_executable = True,
+    )
+    return [
+        DefaultInfo(
+            executable = runner,
+            runfiles = ctx.runfiles(files = files).merge(ctx.attr._worker[DefaultInfo].default_runfiles),
+        ),
+        testing.ExecutionInfo(compiler.execution_requirements),
+        testing.TestEnvironment(compiler.env | {
+            "WORKER_TEST_FILE_HASHING": "1" if SWIFT_FEATURE_INCREMENTAL_FILE_HASHING in toolchain.requested_features else "0",
+        }),
+    ]
+
+worker_test = rule(
+    implementation = _worker_test_impl,
+    attrs = {
+        "scenario": attr.string(mandatory = True),
+        "_observer": attr.label(default = "observe_swiftc.sh", allow_single_file = True),
+        "_script": attr.label(default = "worker_test.sh", allow_single_file = True),
+        "_worker": attr.label(default = "//tools/worker:worker", executable = True, cfg = "exec"),
+    },
+    test = True,
+    toolchains = ["//toolchains:toolchain_type"],
+)