Fix Linux bug

Author: David Ungar

Sources/SwiftDriver/Incremental Compilation/IncrementalCompilationState.swift

@@ -116,8 +116,6 @@ import SwiftOptions
     self.pendingInputs = Set(immediatelyCompiledInputs)
     self.moduleDependencyGraph = moduleDependencyGraph
     self.reportIncrementalDecision = reportIncrementalDecision
-
-    maybeFinishedWithCompilations()
   }
 
   /// Check various arguments to rule out incremental compilation if need be.
@@ -370,14 +368,19 @@ extension IncrementalCompilationState {
 extension IncrementalCompilationState {
   /// Decide if  a job can be skipped, and register accordingly
   func addPreOrCompileJobGroups(_ groups: [[Job]]) {
+    var wereAnyJobsScheduled = false
     for group in groups {
       if let firstJob = group.first, isSkipped(firstJob) {
         recordSkippedGroup(group)
       }
       else {
         schedule(group: group)
+        wereAnyJobsScheduled = true
       }
     }
+    if !wereAnyJobsScheduled {
+      finishedWithCompilations()
+    }
   }
 
   func isSkipped(_ job: Job) -> Bool {
@@ -451,7 +454,9 @@ extension IncrementalCompilationState {
     }
     schedule(compilationInputs: discoveredInputs)
     finishedJob.primaryInputs.forEach {pendingInputs.remove($0)}
-    maybeFinishedWithCompilations()
+    if pendingInputs.isEmpty {
+      finishedWithCompilations()
+    }
  }
 
   private func collectInputsDiscovered(
@@ -483,11 +488,7 @@ extension IncrementalCompilationState {
     schedule(preOrCompileJobs: jobs)
   }
 
-  func maybeFinishedWithCompilations() {
-    guard pendingInputs.isEmpty
-    else {
-      return
-    }
+  func finishedWithCompilations() {
     preOrCompileJobs.enqueue(nil)
   }
 }