Order package manifest to start with the package declaration

Instead of starting with environment variable parsing, start with the actual package manifest, which is most likely the most interesting to most users.

Author: ahoppen

Package.swift

@@ -14,24 +14,6 @@
 import Foundation
 import PackageDescription
 
-// MARK: - Parse build arguments
-
-func hasEnvironmentVariable(_ name: String) -> Bool {
-  return ProcessInfo.processInfo.environment[name] != nil
-}
-
-// When building the toolchain on the CI, don't add the CI's runpath for the
-// final build before installing.
-let installAction = hasEnvironmentVariable("SOURCEKIT_LSP_CI_INSTALL")
-
-
-// MARK: - Compute custom build settings
-
-var swiftformatLinkSettings: [LinkerSetting] = []
-if installAction {
-  swiftformatLinkSettings += [.unsafeFlags(["-no-toolchain-stdlib-rpath"], .when(platforms: [.linux, .android]))]
-}
-
 let package = Package(
   name: "swift-format",
   platforms: [
@@ -56,9 +38,7 @@ let package = Package(
       targets: ["Lint Source Code"]
     ),
   ],
-  dependencies: [
-    // See the "Dependencies" section below.
-  ],
+  dependencies: dependencies,
   targets: [
     .target(
       name: "_SwiftFormatInstructionCounter"
@@ -156,28 +136,47 @@ let package = Package(
   ]
 )
 
-// MARK: Dependencies
+// MARK: - Parse build arguments
 
-if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
-  // Building standalone.
-  package.dependencies += [
-    .package(
-      url: "https://github.com/apple/swift-argument-parser.git", 
-      from: "1.2.2"
-    ),
-    .package(
-      url: "https://github.com/apple/swift-markdown.git",
-      from: "0.2.0"
-    ),
-    .package(
-      url: "https://github.com/apple/swift-syntax.git",
-      branch: "main"
-    ),
-  ]
-} else {
-  package.dependencies += [
-    .package(path: "../swift-argument-parser"),
-    .package(path: "../swift-markdown"),
-    .package(path: "../swift-syntax"),
-  ]
+func hasEnvironmentVariable(_ name: String) -> Bool {
+  return ProcessInfo.processInfo.environment[name] != nil
+}
+
+// When building the toolchain on the CI, don't add the CI's runpath for the
+// final build before installing.
+var installAction: Bool { hasEnvironmentVariable("SOURCEKIT_LSP_CI_INSTALL") }
+
+/// Assume that all the package dependencies are checked out next to sourcekit-lsp and use that instead of fetching a
+/// remote dependency.
+var useLocalDependencies: Bool { hasEnvironmentVariable("SWIFTCI_USE_LOCAL_DEPS") }
+
+// MARK: - Dependencies
+
+var dependencies: [Package.Dependency] {
+  if useLocalDependencies {
+    return [
+      .package(path: "../swift-argument-parser"),
+      .package(path: "../swift-markdown"),
+      .package(path: "../swift-syntax"),
+    ]
+  } else {
+    return [
+      .package(url: "https://github.com/apple/swift-argument-parser.git", from: "1.2.2"),
+      .package(url: "https://github.com/apple/swift-markdown.git", from: "0.2.0"),
+      .package(url: "https://github.com/apple/swift-syntax.git", branch: "main"),
+    ]
+  }
 }
+
+
+
+// MARK: - Compute custom build settings
+
+var swiftformatLinkSettings: [LinkerSetting]  {
+  if installAction {
+    return [.unsafeFlags(["-no-toolchain-stdlib-rpath"], .when(platforms: [.linux, .android]))]
+  } else {
+    return []
+  }
+}
+