[Incremental Builds] Produce an empty first wave if only job to run is verify module interface job.

Existing check decides to skip all compilation if there are no compile jobs and no post-compile job depends on before-compile jobs' outputs. This change refines the check to also ensure we do not run before-compile jobs whose only dependents are interface verification jobs. Otherwise, we would have an emit-module job, followed by verify-module-interface jobs on a null incremental build.

Resolves rdar://89913538

Author: artemcm

Sources/SwiftDriver/IncrementalCompilation/FirstWaveComputer.swift

@@ -128,18 +128,23 @@ extension IncrementalCompilationState.FirstWaveComputer {
     // In the case where there are no compilation jobs to run on this build (no source-files were changed),
     // we can skip running `beforeCompiles` jobs if we also ensure that none of the `afterCompiles` jobs
     // have any dependencies on them.
-    let skipAllJobs = batchedCompilationJobs.isEmpty ? !afterCompileJobsDependOnBeforeCompileJobs() : false
+    let skipAllJobs = batchedCompilationJobs.isEmpty ? !nonVerifyAfterCompileJobsDependOnBeforeCompileJobs() : false
     let mandatoryJobsInOrder = skipAllJobs ? [] : jobsInPhases.beforeCompiles + batchedCompilationJobs
     return (initiallySkippedCompileGroups: initiallySkippedCompileGroups,
             mandatoryJobsInOrder: mandatoryJobsInOrder)
   }
 
   /// Determine if any of the jobs in the `afterCompiles` group depend on outputs produced by jobs in
-  /// `beforeCompiles` group.
-  private func afterCompileJobsDependOnBeforeCompileJobs() -> Bool {
-      let beforeCompileJobOutputs = jobsInPhases.beforeCompiles.reduce(into: Set<TypedVirtualPath>(),
-                                                                       { (pathSet, job) in pathSet.formUnion(job.outputs) })
-      return jobsInPhases.afterCompiles.contains {postCompileJob in postCompileJob.inputs.contains(where: beforeCompileJobOutputs.contains)}
+  /// `beforeCompiles` group, which are not also verification jobs.
+  private func nonVerifyAfterCompileJobsDependOnBeforeCompileJobs() -> Bool {
+    let beforeCompileJobOutputs = jobsInPhases.beforeCompiles.reduce(into: Set<TypedVirtualPath>(),
+                                                                     { (pathSet, job) in pathSet.formUnion(job.outputs) })
+    let afterCompilesDependnigJobs = jobsInPhases.afterCompiles.filter {postCompileJob in postCompileJob.inputs.contains(where: beforeCompileJobOutputs.contains)}
+    if afterCompilesDependnigJobs.isEmpty || afterCompilesDependnigJobs.allSatisfy({ $0.kind == .verifyModuleInterface }) {
+      return false
+    } else {
+      return true
+    }
   }
 
   /// Figure out which compilation inputs are *not* mandatory at the start

Tests/SwiftDriverTests/IncrementalCompilationTests.swift

@@ -331,6 +331,14 @@ extension IncrementalCompilationTests {
     XCTAssertTrue(mandatoryJobs.isEmpty)
   }
 
+    func testNullBuildNoVerify() throws {
+      let extraArguments = ["-experimental-emit-module-separately", "-emit-module", "-emit-module-interface", "-enable-library-evolution", "-verify-emitted-module-interface"]
+      try buildInitialState(extraArguments: extraArguments)
+      let driver = try checkNullBuild(extraArguments: extraArguments)
+      let mandatoryJobs = try XCTUnwrap(driver.incrementalCompilationState?.mandatoryJobsInOrder)
+      XCTAssertTrue(mandatoryJobs.isEmpty)
+    }
+
   func testSymlinkModification() throws {
     // Remap
     // main.swift -> links/main.swift