Remove build record if module dependency graph write fails

Author: David Ungar

Sources/SwiftDriver/Driver/Driver.swift

@@ -971,10 +971,7 @@ extension Driver {
     if !childJobs.isEmpty {
       do {
         defer {
-          self.incrementalCompilationState?.writeDependencyGraph()
-          buildRecordInfo?.writeBuildRecord(
-            jobs,
-            incrementalCompilationState?.skippedCompilationInputs)
+          writeIncrementalBuildInformation(jobs)
         }
         try performTheBuild(allJobs: childJobs,
                             jobExecutionDelegate: toolExecutionDelegate,
@@ -1038,6 +1035,20 @@ extension Driver {
       recordedInputModificationDates: recordedInputModificationDates)
   }
 
+  private func writeIncrementalBuildInformation(_ jobs: [Job]) {
+    if let incrementalCompilationState = self.incrementalCompilationState {
+      let hadError = incrementalCompilationState.writeDependencyGraph()
+      /// Ensure that a bogus dependency graph is not used next time
+      guard !hadError else {
+        buildRecordInfo?.removeBuildRecord()
+        return
+      }
+    }
+    buildRecordInfo?.writeBuildRecord(
+      jobs,
+      incrementalCompilationState?.skippedCompilationInputs)
+  }
+
   private func printBindings(_ job: Job) {
     stdoutStream <<< #"# ""# <<< targetTriple.triple
     stdoutStream <<< #"" - ""# <<< job.tool.basename

Sources/SwiftDriver/IncrementalCompilation/BuildRecordInfo.swift

@@ -184,6 +184,13 @@ import SwiftOptions
     }
   }
 
+  func removeBuildRecord() {
+    guard let absPath = buildRecordPath.absolutePath else {
+      return
+    }
+    try? fileSystem.removeFileTree(absPath)
+  }
+
   /// Before writing to the dependencies file path, preserve any previous file
   /// that may have been there. No error handling -- this is just a nicety, it
   /// doesn't matter if it fails.

Sources/SwiftDriver/IncrementalCompilation/IncrementalCompilationState.swift

@@ -444,23 +444,26 @@ extension IncrementalCompilationState {
 // MARK: - Serialization
 
 extension IncrementalCompilationState {
-  @_spi(Testing) public func writeDependencyGraph() {
+  @_spi(Testing) public func writeDependencyGraph() -> Bool {
     // If the cross-module build is not enabled, the status quo dictates we
     // not emit this file.
     guard moduleDependencyGraph.info.isCrossModuleIncrementalBuildEnabled else {
-      return
+      return false
     }
 
     guard
       let recordInfo = self.driver.buildRecordInfo
     else {
+      // It's OK to silently fail because no build record will be written
+      // so there will be no attempt to use the saved module dependency graph
+      // next time.
       self.driver.diagnosticEngine.emit(
         .warning_could_not_write_dependency_graph)
-      return
+      return true
     }
-    self.moduleDependencyGraph.write(to: recordInfo.dependencyGraphPath,
-                                     on: self.driver.fileSystem,
-                                     compilerVersion: recordInfo.actualSwiftVersion)
+    return self.moduleDependencyGraph.write(to: recordInfo.dependencyGraphPath,
+                                            on: self.driver.fileSystem,
+                                            compilerVersion: recordInfo.actualSwiftVersion)
   }
 }
 

Sources/SwiftDriver/IncrementalCompilation/ModuleDependencyGraph.swift

@@ -663,19 +663,22 @@ extension ModuleDependencyGraph {
   ///   - fileSystem: The file system for this location.
   ///   - compilerVersion: A string containing version information for the
   ///                      driver used to create this file.
+  /// - Returns: true if had error
   @_spi(Testing) public func write(
     to path: VirtualPath,
     on fileSystem: FileSystem,
     compilerVersion: String
-  ) {
+  ) -> Bool {
     let data = ModuleDependencyGraph.Serializer.serialize(self, compilerVersion)
 
     do {
       try fileSystem.writeFileContents(path,
                                        bytes: data,
                                        atomically: true)
+      return false
     } catch {
       info.diagnosticEngine.emit(.warning_could_not_write_dep_graph(to: path, error: error))
+      return true
     }
   }