Pass --explicit-target-dependency-import-check error when building swift-syntax

This should catch missing imports such as swiftlang#3195

Author: ahoppen

.github/workflows/pull_request.yml

@@ -19,6 +19,8 @@ jobs:
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
     with:
       enable_wasm_sdk_build: true
+      linux_build_command: "swift test --explicit-target-dependency-import-check error"
+      windows_build_command: "Invoke-Program swift test --explicit-target-dependency-import-check error"
   soundness:
     name: Soundness
     uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main

SwiftSyntaxDevUtils/Sources/swift-syntax-dev-utils/common/SwiftPMBuilder.swift

@@ -83,7 +83,10 @@ struct SwiftPMBuilder {
     if action == "test" {
       args += ["--disable-testable-imports"]
     }
-    args += ["--package-path", packageDir.path]
+    args += [
+      "--package-path", packageDir.path,
+      "--explicit-target-dependency-import-check", "error",
+    ]
 
     if let buildDir = buildDir?.path {
       args += ["--scratch-path", buildDir]