Revert "Use libSwiftScan to query supported compiler flags in-process"

Author: DougGregor

Sources/SwiftDriver/Jobs/EmitSupportedFeaturesJob.swift

@@ -13,7 +13,7 @@
 import SwiftOptions
 import struct Foundation.Data
 import class Foundation.JSONDecoder
-import struct TSCBasic.Diagnostic
+
 import class TSCBasic.DiagnosticsEngine
 import protocol TSCBasic.FileSystem
 import struct TSCBasic.RelativePath
@@ -56,27 +56,27 @@ extension Toolchain {
   }
 }
 
-extension Diagnostic.Message {
-  static func warn_supported_features_frontend_fallback() -> Diagnostic.Message {
-    .warning("Fallback to `swift-frontend` for supported compiler features query")
-  }
-}
-
 extension Driver {
-  static func computeSupportedCompilerArgs(of toolchain: Toolchain,
-                                           hostTriple: Triple,
-                                           parsedOptions: inout ParsedOptions,
-                                           diagnosticsEngine: DiagnosticsEngine,
-                                           fileSystem: FileSystem,
-                                           executor: DriverExecutor, env: [String: String])
+  static func computeSupportedCompilerArgs(of toolchain: Toolchain, hostTriple: Triple,
+                                               parsedOptions: inout ParsedOptions,
+                                               diagnosticsEngine: DiagnosticsEngine,
+                                               fileSystem: FileSystem,
+                                               executor: DriverExecutor, env: [String: String])
   throws -> Set<String> {
-    if let supportedArgs = try querySupportedCompilerArgsInProcess(of: toolchain, hostTriple: hostTriple,
-                                                                   fileSystem: fileSystem, env: env) {
-      return supportedArgs
-    }
+    // TODO: Once we are sure libSwiftScan is deployed across supported platforms and architectures
+    // we should deploy it here.
+//    let swiftScanLibPath = try Self.getScanLibPath(of: toolchain,
+//                                                   hostTriple: hostTriple,
+//                                                   env: env)
+//
+//    if fileSystem.exists(swiftScanLibPath) {
+//      let libSwiftScanInstance = try SwiftScan(dylib: swiftScanLibPath)
+//      if libSwiftScanInstance.canQuerySupportedArguments() {
+//        return try libSwiftScanInstance.querySupportedArguments()
+//      }
+//    }
 
-    // Fallback: Invoke `swift-frontend -emit-supported-features` and decode the output
-    diagnosticsEngine.emit(.warn_supported_features_frontend_fallback())
+    // Invoke `swift-frontend -emit-supported-features`
     let frontendOverride = try FrontendOverride(&parsedOptions, diagnosticsEngine)
     frontendOverride.setUpForTargetInfo(toolchain)
     defer { frontendOverride.setUpForCompilation(toolchain) }
@@ -91,23 +91,6 @@ extension Driver {
     return Set(decodedSupportedFlagList)
   }
 
-  static func querySupportedCompilerArgsInProcess(of toolchain: Toolchain,
-                                                  hostTriple: Triple,
-                                                  fileSystem: FileSystem,
-                                                  env: [String: String])
-  throws -> Set<String>? {
-    let swiftScanLibPath = try Self.getScanLibPath(of: toolchain,
-                                                   hostTriple: hostTriple,
-                                                   env: env)
-    if fileSystem.exists(swiftScanLibPath) {
-      let libSwiftScanInstance = try SwiftScan(dylib: swiftScanLibPath)
-      if libSwiftScanInstance.canQuerySupportedArguments() {
-        return try libSwiftScanInstance.querySupportedArguments()
-      }
-    }
-    return nil
-  }
-
   static func computeSupportedCompilerFeatures(of toolchain: Toolchain,
                                                env: [String: String]) throws -> Set<String> {
     struct FeatureInfo: Codable {