Swift: Emit a diagnostic when attempting to use the autobuilder on Linux.

swift/BUILD.bazel

@@ -57,6 +57,12 @@ pkg_runfiles(
     prefix = "tools/" + codeql_platform,
 )
 
+pkg_runfiles(
+    name = "incompatible-os",
+    srcs = ["//swift/tools/autobuilder-diagnostics:incompatible-os"],
+    prefix = "tools/" + codeql_platform,
+)
+
 pkg_files(
     name = "swift-test-sdk-arch",
     srcs = ["//swift/third_party/swift-llvm-support:swift-test-sdk"],
@@ -70,7 +76,9 @@ pkg_filegroup(
         ":extractor",
         ":swift-test-sdk-arch",
     ] + select({
-        "@platforms//os:linux": [],
+        "@platforms//os:linux": [
+            ":incompatible-os",
+        ],
         "@platforms//os:macos": [
             ":xcode-autobuilder",
         ],

swift/integration-tests/linux-only/autobuilder/unsupported-os/diagnostics.expected

@@ -0,0 +1,19 @@
+{
+  "helpLinks": [
+    "https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions#jobsjob_idruns-on",
+    "https://docs.github.com/en/enterprise-server/code-security/code-scanning/automatically-scanning-your-code-for-vulnerabilities-and-errors/customizing-code-scanning",
+    "https://docs.github.com/en/enterprise-server/code-security/code-scanning/automatically-scanning-your-code-for-vulnerabilities-and-errors/configuring-the-codeql-workflow-for-compiled-languages#adding-build-steps-for-a-compiled-language"
+  ],
+  "plaintextMessage": "CodeQL Swift analysis is currently only officially supported on macOS.\n\nChange the action runner to a macOS one. Analysis on Linux might work, but requires setting up a custom build command.",
+  "severity": "error",
+  "source": {
+    "extractorName": "swift",
+    "id": "swift/autobuilder/incompatible-os",
+    "name": "Incompatible operating system for autobuild (expected macOS)"
+  },
+  "visibility": {
+    "cliSummaryTable": true,
+    "statusPage": true,
+    "telemetry": true
+  }
+}

swift/integration-tests/linux-only/autobuilder/unsupported-os/test.py

@@ -0,0 +1,5 @@
+from create_database_utils import *
+from diagnostics_test_utils import *
+
+run_codeql_database_create([], lang='swift', keep_trap=True, db=None, runFunction=runUnsuccessfully)
+check_diagnostics()

swift/tools/autobuild.sh

@@ -3,6 +3,5 @@
 if [[ "$OSTYPE" == "darwin"* ]]; then
   exec "${CODEQL_EXTRACTOR_SWIFT_ROOT}/tools/${CODEQL_PLATFORM}/xcode-autobuilder"
 else
-  echo "Not implemented yet"
-  exit 1
+  exec "${CODEQL_EXTRACTOR_SWIFT_ROOT}/tools/${CODEQL_PLATFORM}/incompatible-os"
 fi

swift/tools/autobuilder-diagnostics/BUILD.bazel

@@ -0,0 +1,17 @@
+load("//swift:rules.bzl", "swift_cc_binary")
+load("//misc/bazel/cmake:cmake.bzl", "generate_cmake")
+
+swift_cc_binary(
+    name = "incompatible-os",
+    srcs = ["IncompatibleOs.cpp"],
+    visibility = ["//swift:__subpackages__"],
+    deps = [
+        "//swift/logging",
+    ],
+)
+
+generate_cmake(
+    name = "cmake",
+    targets = [":incompatible-os"],
+    visibility = ["//visibility:public"],
+)

swift/tools/autobuilder-diagnostics/IncompatibleOs.cpp

@@ -0,0 +1,35 @@
+// Unconditionally emits a diagnostic about running the autobuilder on an incompatible, non-macOS OS
+// and exits with an error code.
+//
+// This is implemented as a C++ binary instead of a hardcoded JSON file so we can leverage existing
+// diagnostic machinery for emitting correct timestamps, generating correct file names, etc.
+
+#include "swift/logging/SwiftLogging.h"
+
+const std::string_view codeql::programName = "autobuilder";
+
+namespace codeql_diagnostics {
+constexpr codeql::SwiftDiagnosticsSource incompatible_os{
+    "incompatible_os", "Incompatible operating system for autobuild (expected macOS)",
+    "Change the action runner to a macOS one. Analysis on Linux might work, but requires setting "
+    "up a custom build command",
+    "https://docs.github.com/en/actions/using-workflows/"
+    "workflow-syntax-for-github-actions#jobsjob_idruns-on "
+    "https://docs.github.com/en/enterprise-server/code-security/code-scanning/"
+    "automatically-scanning-your-code-for-vulnerabilities-and-errors/customizing-code-scanning "
+    "https://docs.github.com/en/enterprise-server/code-security/code-scanning/"
+    "automatically-scanning-your-code-for-vulnerabilities-and-errors/"
+    "configuring-the-codeql-workflow-for-compiled-languages#adding-build-steps-for-a-compiled-"
+    "language"};
+}  // namespace codeql_diagnostics
+
+static codeql::Logger& logger() {
+  static codeql::Logger ret{"main"};
+  return ret;
+}
+
+int main() {
+  DIAGNOSE_ERROR(incompatible_os,
+                 "CodeQL Swift analysis is currently only officially supported on macOS");
+  return 1;
+}