Swift: wrap extractor with shell script

This is in preparation for the extractor to use shared libraries
packaged alongside it.

We could probably also move the `CODEQL_EXTRACTOR_SWIFT_RUN_UNDER` logic
in it, where it would be simpler and more robust.

Author: redsun82

swift/BUILD.bazel

@@ -39,9 +39,9 @@ pkg_filegroup(
     visibility = ["//visibility:public"],
 )
 
-pkg_runfiles(
+pkg_filegroup(
     name = "extractor",
-    srcs = ["//swift/extractor"],
+    srcs = ["//swift/extractor:pkg"],
     prefix = "tools/" + codeql_platform,
 )
 

swift/extractor/BUILD.bazel

@@ -1,13 +1,13 @@
 load("//swift:rules.bzl", "swift_cc_binary")
 load("//misc/bazel/cmake:cmake.bzl", "generate_cmake")
+load("//misc/bazel:pkg_runfiles.bzl", "pkg_runfiles")
 
 swift_cc_binary(
-    name = "extractor",
+    name = "extractor.real",
     srcs = glob([
         "*.h",
         "*.cpp",
     ]),
-    visibility = ["//swift:__pkg__"],
     deps = [
         "//swift/extractor/infra",
         "//swift/extractor/invocation",
@@ -19,6 +19,19 @@ swift_cc_binary(
 
 generate_cmake(
     name = "cmake",
-    targets = [":extractor"],
+    targets = [":extractor.real"],
     visibility = ["//visibility:public"],
 )
+
+sh_binary(
+    name = "extractor",
+    srcs = ["extractor.sh"],
+    data = [":extractor.real"],
+)
+
+pkg_runfiles(
+    name = "pkg",
+    srcs = [":extractor"],
+    excludes = ["extractor.sh"],  # script gets copied as "extractor", no need for the original .sh file
+    visibility = ["//swift:__pkg__"],
+)

swift/extractor/extractor.sh

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+if [[ "$(uname)" == Darwin ]]; then
+  export DYLD_FALLBACK_LIBRARY_PATH=$(dirname "$0")
+else
+  export LD_LIBRARY_PATH=$(dirname "$0")
+fi
+
+exec -a "$0" "$0.real" "$@"