[Dependency Scanning] Deprecate/Remove inter-module dependency graph serialization SwiftScan API uses

This mechanism relied on serializing contents of a dependency scanner cache that included all queried scanning contexts. Instead, the scanner will move to a per-query serialization format.
These API were never actually deployed and, to our knowledge, have not worked for a long time.

Compiler-side change: swiftlang/swift#77794

Author: artemcm

Sources/CSwiftScan/include/swiftscan_header.h

@@ -259,11 +259,6 @@ typedef struct {
   int64_t
   (*swiftscan_source_location_get_column_number)(swiftscan_source_location_t);
 
-  //=== Scanner Cache Functions ---------------------------------------------===//
-  void (*swiftscan_scanner_cache_serialize)(swiftscan_scanner_t scanner, const char * path);
-  bool (*swiftscan_scanner_cache_load)(swiftscan_scanner_t scanner, const char * path);
-  void (*swiftscan_scanner_cache_reset)(swiftscan_scanner_t scanner);
-
   //=== Scanner CAS Operations ----------------------------------------------===//
   swiftscan_cas_options_t (*swiftscan_cas_options_create)(void);
   int64_t (*swiftscan_cas_get_ondisk_size)(swiftscan_cas_t,

Sources/SwiftDriver/ExplicitModuleBuilds/InterModuleDependencies/InterModuleDependencyOracle.swift

@@ -90,34 +90,6 @@ public class InterModuleDependencyOracle {
     }
   }
 
-  @_spi(Testing) public func serializeScannerCache(to path: AbsolutePath) {
-    guard let swiftScan = swiftScanLibInstance else {
-      fatalError("Attempting to serialize scanner cache with no scanner instance.")
-    }
-    if swiftScan.canLoadStoreScannerCache {
-      swiftScan.serializeScannerCache(to: path)
-    }
-  }
-
-  @_spi(Testing) public func loadScannerCache(from path: AbsolutePath) -> Bool {
-    guard let swiftScan = swiftScanLibInstance else {
-      fatalError("Attempting to load scanner cache with no scanner instance.")
-    }
-    if swiftScan.canLoadStoreScannerCache {
-      return swiftScan.loadScannerCache(from: path)
-    }
-    return false
-  }
-
-  @_spi(Testing) public func resetScannerCache() {
-    guard let swiftScan = swiftScanLibInstance else {
-      fatalError("Attempting to reset scanner cache with no scanner instance.")
-    }
-    if swiftScan.canLoadStoreScannerCache {
-      swiftScan.resetScannerCache()
-    }
-  }
-
   @_spi(Testing) public func supportsBinaryFrameworkDependencies() throws -> Bool {
     guard let swiftScan = swiftScanLibInstance else {
       fatalError("Attempting to query supported scanner API with no scanner instance.")

Sources/SwiftDriver/SwiftScan/SwiftScan.swift

@@ -228,12 +228,6 @@ private extension String {
     api.swiftscan_swift_binary_detail_get_header_dependency_module_dependencies != nil
   }
 
-  @_spi(Testing) public var canLoadStoreScannerCache : Bool {
-    api.swiftscan_scanner_cache_load != nil &&
-    api.swiftscan_scanner_cache_serialize != nil &&
-    api.swiftscan_scanner_cache_reset != nil
-  }
-
   @_spi(Testing) public var clangDetailsHaveCapturedPCMArgs : Bool {
     api.swiftscan_clang_detail_get_captured_pcm_args != nil
   }
@@ -319,20 +313,6 @@ private extension String {
            api.swiftscan_link_library_info_get_should_force_load != nil
   }
 
-  func serializeScannerCache(to path: AbsolutePath) {
-    api.swiftscan_scanner_cache_serialize(scanner,
-                                          path.description.cString(using: String.Encoding.utf8))
-  }
-
-  func loadScannerCache(from path: AbsolutePath) -> Bool {
-    return api.swiftscan_scanner_cache_load(scanner,
-                                            path.description.cString(using: String.Encoding.utf8))
-  }
-
-  func resetScannerCache() {
-    api.swiftscan_scanner_cache_reset(scanner)
-  }
-
   internal func mapToDriverDiagnosticPayload(_ diagnosticSetRef: UnsafeMutablePointer<swiftscan_diagnostic_set_t>) throws -> [ScannerDiagnosticPayload] {
     var result: [ScannerDiagnosticPayload] = []
     let diagnosticRefArray = Array(UnsafeBufferPointer(start: diagnosticSetRef.pointee.diagnostics,
@@ -497,14 +477,6 @@ private extension swiftscan_functions_t {
     self.swiftscan_compiler_target_info_query_v2 =
       loadOptional("swiftscan_compiler_target_info_query_v2")
 
-    // Dependency scanner serialization/deserialization features
-    self.swiftscan_scanner_cache_serialize =
-      loadOptional("swiftscan_scanner_cache_serialize")
-    self.swiftscan_scanner_cache_load =
-      loadOptional("swiftscan_scanner_cache_load")
-    self.swiftscan_scanner_cache_reset =
-      loadOptional("swiftscan_scanner_cache_reset")
-
     // Clang dependency captured PCM args
     self.swiftscan_clang_detail_get_captured_pcm_args =
       loadOptional("swiftscan_clang_detail_get_captured_pcm_args")

Tests/SwiftDriverTests/ExplicitModuleBuildTests.swift

@@ -2172,71 +2172,6 @@ final class ExplicitModuleBuildTests: XCTestCase {
       }
   }
 
-  /// Test the libSwiftScan dependency scanning.
-  func testDependencyScanReuseCache() throws {
-    let (stdlibPath, shimsPath, toolchain, _) = try getDriverArtifactsForScanning()
-    try withTemporaryDirectory { path in
-      let cacheSavePath = path.appending(component: "saved.moddepcache")
-      let main = path.appending(component: "testDependencyScanning.swift")
-      try localFileSystem.writeFileContents(main, bytes:
-        """
-        import C;\
-        import E;\
-        import G;
-        """
-      )
-
-      let cHeadersPath: AbsolutePath =
-          try testInputsPath.appending(component: "ExplicitModuleBuilds")
-                            .appending(component: "CHeaders")
-      let swiftModuleInterfacesPath: AbsolutePath =
-          try testInputsPath.appending(component: "ExplicitModuleBuilds")
-                            .appending(component: "Swift")
-      let sdkArgumentsForTesting = (try? Driver.sdkArgumentsForTesting()) ?? []
-      var driver = try Driver(args: ["swiftc",
-                                     "-I", cHeadersPath.nativePathString(escaped: true),
-                                     "-I", swiftModuleInterfacesPath.nativePathString(escaped: true),
-                                     "-I", stdlibPath.nativePathString(escaped: true),
-                                     "-I", shimsPath.nativePathString(escaped: true),
-                                     "-explicit-module-build",
-                                     "-working-directory", path.nativePathString(escaped: true),
-                                     "-disable-clang-target",
-                                     main.nativePathString(escaped: true)] + sdkArgumentsForTesting,
-                              env: ProcessEnv.vars)
-      let resolver = try ArgsResolver(fileSystem: localFileSystem)
-      var scannerCommand = try driver.dependencyScannerInvocationCommand().1.map { try resolver.resolve($0) }
-      // We generate full swiftc -frontend -scan-dependencies invocations in order to also be
-      // able to launch them as standalone jobs. Frontend's argument parser won't recognize
-      // -frontend when passed directly via libSwiftScan.
-      if scannerCommand.first == "-frontend" {
-        scannerCommand.removeFirst()
-      }
-
-      let scanLibPath = try XCTUnwrap(toolchain.lookupSwiftScanLib())
-      // Run the first scan and serialize the cache contents.
-      let firstDependencyOracle = InterModuleDependencyOracle()
-      try firstDependencyOracle.verifyOrCreateScannerInstance(swiftScanLibPath: scanLibPath)
-      var firstScanDiagnostics: [ScannerDiagnosticPayload] = []
-      let firstScanGraph =
-        try firstDependencyOracle.getDependencies(workingDirectory: path,
-                                              commandLine: scannerCommand,
-                                              diagnostics: &firstScanDiagnostics)
-      firstDependencyOracle.serializeScannerCache(to: cacheSavePath)
-
-      // Run the second scan, re-using the serialized cache contents.
-      let secondDependencyOracle = InterModuleDependencyOracle()
-      try secondDependencyOracle.verifyOrCreateScannerInstance(swiftScanLibPath: scanLibPath)
-      XCTAssertFalse(secondDependencyOracle.loadScannerCache(from: cacheSavePath))
-      var secondScanDiagnostics: [ScannerDiagnosticPayload] = []
-      let secondScanGraph =
-        try secondDependencyOracle.getDependencies(workingDirectory: path,
-                                                   commandLine: scannerCommand,
-                                                   diagnostics: &secondScanDiagnostics)
-
-      XCTAssertTrue(firstScanGraph.modules.count == secondScanGraph.modules.count)
-    }
-  }
-
   func testDependencyScanCommandLineEscape() throws {
 #if os(Windows)
   let quoteCharacter: Character = "\""