Remove Package.resolved and move to HEAD

Always use the latest indexstore-db and swiftpm from the corresponding
branch (currently master). This is important for swiftpm, because it
does not *guarantee* stable behaviour, so we need to match the version.
It also makes sourcekit-lsp behave more like the rest of the swift
toolchain projects, who all live on HEAD for their dependencies.

Author: benlangmuir

.gitignore

@@ -1,5 +1,6 @@
 .DS_Store
 default.profraw
+Package.resolved
 /.build
 /Packages
 /*.xcodeproj

Package.resolved

@@ -7,8 +7,7 @@ let package = Package(
     products: [
     ],
     dependencies: [
-      .package(url: "https://github.com/apple/swift-package-manager.git", .branch("master")),
-      .package(url: "https://github.com/apple/indexstore-db.git", .branch("master")),
+      // See 'Dependencies' below.
     ],
     targets: [
       .target(
@@ -82,3 +81,28 @@ let package = Package(
         dependencies: ["SKSupport", "SKTestSupport"]),
     ]
 )
+
+// MARK: Dependencies
+
+// When building with the swift build-script, use local dependencies whose contents are controlled
+// by the external environment. This allows sourcekit-lsp to take advantage of the automation used
+// for building the swift toolchain, such as `update-checkout`, or cross-repo PR tests.
+
+#if os(Linux)
+import Glibc
+#else
+import Darwin.C
+#endif
+
+if getenv("SWIFTCI_USE_LOCAL_DEPS") == nil {
+  // Building standalone.
+  package.dependencies += [
+    .package(url: "https://github.com/apple/indexstore-db.git", .branch("master")),
+    .package(url: "https://github.com/apple/swift-package-manager.git", .branch("master")),
+  ]
+} else {
+  package.dependencies += [
+    .package(path: "../indexstore-db"),
+    .package(path: "../swiftpm"),
+  ]
+}

Package.swift

@@ -66,15 +66,18 @@ def add_common_args(parser):
 
   swiftpm_args = get_swiftpm_options(args)
 
+  env = os.environ
+  # Set the toolchain used in tests at runtime
+  env['SOURCEKIT_TOOLCHAIN_PATH'] = args.toolchain
+  # Use local dependencies (i.e. checked out next sourcekit-lsp).
+  env['SWIFTCI_USE_LOCAL_DEPS'] = "1"
+
   if args.action == 'build':
-    swiftpm('build', swift_exec, swiftpm_args)
+    swiftpm('build', swift_exec, swiftpm_args, env)
   elif args.action == 'test':
-    # Set the toolchain used in tests at runtime
-    env = os.environ
-    env['SOURCEKIT_TOOLCHAIN_PATH'] = args.toolchain
     swiftpm('test', swift_exec, swiftpm_args, env)
   else:
     assert False, 'unknown action \'{}\''.format(args.action)
 
 if __name__ == '__main__':
-  main()
+  main()