Throw instead of return hadError

Author: David Ungar

Sources/SwiftDriver/Driver/Driver.swift

@@ -1057,11 +1057,15 @@ extension Driver {
     // A mitigation to rdar://76359678.
     // If the write fails, import incrementality is lost, but it is not a fatal error.
     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
+      do {
+        try incrementalCompilationState.writeDependencyGraph()
+      }
+      catch {
+        diagnosticEngine.emit(
+          .warning("next compile won't be incremental; could not write dependency graph: \(error.localizedDescription)"))
+          /// Ensure that a bogus dependency graph is not used next time.
+          buildRecordInfo?.removeBuildRecord()
+          return
       }
     }
     buildRecordInfo?.writeBuildRecord(

Sources/SwiftDriver/IncrementalCompilation/IncrementalCompilationState.swift

@@ -223,10 +223,6 @@ extension Diagnostic.Message {
   fileprivate static func remark_incremental_compilation(because why: String) -> Diagnostic.Message {
     .remark("Incremental compilation: \(why)")
   }
-
-  fileprivate static var warning_could_not_write_dependency_graph: Diagnostic.Message {
-    .warning("next compile won't be incremental; could not write dependency graph")
-  }
 }
 
 // MARK: - Scheduling the 2nd wave
@@ -496,26 +492,32 @@ extension IncrementalCompilationState {
 // MARK: - Serialization
 
 extension IncrementalCompilationState {
-  @_spi(Testing) public func writeDependencyGraph() -> Bool {
+  enum WriteDependencyGraphError: LocalizedError {
+    case noBuildRecordInfo,
+         couldNotWrite(path: VirtualPath, error: Error)
+    var errorDescription: String? {
+      switch self {
+      case .noBuildRecordInfo:
+        return "No build record information"
+      case let .couldNotWrite(path, error):
+        return "Could not write to \(path), error: \(error.localizedDescription)"
+      }
+    }
+  }
+  @_spi(Testing) public func writeDependencyGraph() throws {
     // If the cross-module build is not enabled, the status quo dictates we
     // not emit this file.
     guard moduleDependencyGraph.info.isCrossModuleIncrementalBuildEnabled else {
-      return false
+      return
     }
-
     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 true
-    }
-    return self.moduleDependencyGraph.write(to: recordInfo.dependencyGraphPath,
-                                            on: self.driver.fileSystem,
-                                            compilerVersion: recordInfo.actualSwiftVersion)
+      throw WriteDependencyGraphError.noBuildRecordInfo
+    }
+    try self.moduleDependencyGraph.write(to: recordInfo.dependencyGraphPath,
+                                         on: self.driver.fileSystem,
+                                         compilerVersion: recordInfo.actualSwiftVersion)
   }
 }
 

Sources/SwiftDriver/IncrementalCompilation/ModuleDependencyGraph.swift

@@ -668,17 +668,16 @@ extension ModuleDependencyGraph {
     to path: VirtualPath,
     on fileSystem: FileSystem,
     compilerVersion: String
-  ) -> Bool {
+  ) throws {
     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
+      throw IncrementalCompilationState.WriteDependencyGraphError.couldNotWrite(
+        path: path, error: error)
     }
   }
 
@@ -1037,15 +1036,6 @@ fileprivate extension DependencyKey.Designator {
   }
 }
 
-extension Diagnostic.Message {
-  fileprivate static func warning_could_not_write_dep_graph(
-    to path: VirtualPath,
-    error: Error
-  ) -> Diagnostic.Message {
-    .warning("could not write driver dependency graph to \(path), Returned error was: \(error.localizedDescription)")
-  }
-}
-
 // MARK: - Checking Serialization
 
 extension ModuleDependencyGraph {

Tests/SwiftDriverTests/DependencyGraphSerializationTests.swift

@@ -18,7 +18,7 @@ class DependencyGraphSerializationTests: XCTestCase {
   func roundTrip(_ graph: ModuleDependencyGraph) throws {
     let mockPath = VirtualPath.absolute(AbsolutePath("/module-dependency-graph"))
     let fs = InMemoryFileSystem()
-    graph.write(to: mockPath, on: fs, compilerVersion: "Swift 99")
+    try graph.write(to: mockPath, on: fs, compilerVersion: "Swift 99")
 
     let deserializedGraph = try ModuleDependencyGraph.read(from: mockPath,
                                                            info: .mock(fileSystem: fs))!