Teach sourcekit-lsp diagnose how to reduce swift-frontend crashes

`sourcekit-lsp diagnose` tries to automatically scrape crash reports on the user’s machine for compiler arguments. If it finds any, it tries to reduce that swift-frontend crash.

Alternatively, a swift-frontend crash can be reduced by running `sourcekit-lsp reduce-frontend [--toolchain /path/to/toolchain] --frontend-args -all -the frontend --args`

Author: ahoppen

Sources/Diagnose/CMakeLists.txt

@@ -1,15 +1,21 @@
 add_library(Diagnose STATIC
   CommandLineArgumentsReducer.swift
   DiagnoseCommand.swift
+  MergeSwiftFiles.swift
   OSLogScraper.swift
   ReduceCommand.swift
+  ReduceFrontendCommand.swift
+  ReduceSourceKitDRequest.swift
+  ReduceSwiftFrontend.swift
   ReductionError.swift
   ReproducerBundle.swift
   RequestInfo.swift
   SourceKitD+RunWithYaml.swift
   SourceKitDRequestExecutor.swift
+  SourceReducer.swift
   SourcekitdRequestCommand.swift
-  SourceReducer.swift)
+  SwiftFrontendCrashScraper.swift
+  Toolchain+SwiftFrontend.swift)
 
 set_target_properties(Diagnose PROPERTIES
   INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_Swift_MODULE_DIRECTORY})

Sources/Diagnose/CommandLineArgumentsReducer.swift

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
+import LSPLogging
 
 // MARK: - Entry point
 
@@ -48,60 +49,65 @@ fileprivate class CommandLineArgumentReducer {
     self.progressUpdate = progressUpdate
   }
 
-  func logSuccessfulReduction(_ requestInfo: RequestInfo) {
-    progressUpdate(
-      1 - (Double(requestInfo.compilerArgs.count) / Double(initialCommandLineCount)),
-      "Reduced compiler arguments to \(requestInfo.compilerArgs.count)"
-    )
+  func run(initialRequestInfo: RequestInfo) async throws -> RequestInfo {
+    var requestInfo = initialRequestInfo
+    requestInfo = try await reduce(initialRequestInfo: requestInfo, simultaneousRemove: 10)
+    requestInfo = try await reduce(initialRequestInfo: requestInfo, simultaneousRemove: 1)
+    return requestInfo
   }
 
-  func run(initialRequestInfo: RequestInfo) async throws -> RequestInfo {
+  /// Reduce the command line arguments of the given `RequestInfo`.
+  ///
+  /// If `simultaneousRemove` is set, the reducer will try to remove that many arguments at once. This is useful to
+  /// quickly remove multiple arguments from the request.
+  private func reduce(initialRequestInfo: RequestInfo, simultaneousRemove: Int) async throws -> RequestInfo {
+    guard initialRequestInfo.compilerArgs.count > simultaneousRemove else {
+      // Trying to remove more command line arguments than we have. This isn't going to work.
+      return initialRequestInfo
+    }
+
     var requestInfo = initialRequestInfo
     self.initialCommandLineCount = requestInfo.compilerArgs.count
 
     var argumentIndexToRemove = requestInfo.compilerArgs.count - 1
-    while argumentIndexToRemove >= 0 {
-      var numberOfArgumentsToRemove = 1
+    while argumentIndexToRemove + 1 >= simultaneousRemove {
+      defer {
+        // argumentIndexToRemove can become negative by being decremented in the code below
+        let progress = 1 - (Double(max(argumentIndexToRemove, 0)) / Double(initialCommandLineCount))
+        progressUpdate(progress, "Reduced compiler arguments to \(requestInfo.compilerArgs.count)")
+      }
+      var numberOfArgumentsToRemove = simultaneousRemove
       // If the argument is preceded by -Xswiftc or -Xcxx, we need to remove the `-X` flag as well.
-      if argumentIndexToRemove - numberOfArgumentsToRemove >= 0
-        && requestInfo.compilerArgs[argumentIndexToRemove - numberOfArgumentsToRemove].hasPrefix("-X")
-      {
+      if requestInfo.compilerArgs[safe: argumentIndexToRemove - numberOfArgumentsToRemove]?.hasPrefix("-X") ?? false {
         numberOfArgumentsToRemove += 1
       }
 
-      if let reduced = try await tryRemoving(
-        (argumentIndexToRemove - numberOfArgumentsToRemove + 1)...argumentIndexToRemove,
-        from: requestInfo
-      ) {
+      let rangeToRemove = (argumentIndexToRemove - numberOfArgumentsToRemove + 1)...argumentIndexToRemove
+      if let reduced = try await tryRemoving(rangeToRemove, from: requestInfo) {
         requestInfo = reduced
         argumentIndexToRemove -= numberOfArgumentsToRemove
         continue
       }
 
-      // If removing the argument failed and the argument is preceded by an argument starting with `-`, try removing that as well.
-      // E.g. removing `-F` followed by a search path.
-      if argumentIndexToRemove - numberOfArgumentsToRemove >= 0
-        && requestInfo.compilerArgs[argumentIndexToRemove - numberOfArgumentsToRemove].hasPrefix("-")
-      {
+      // If removing the argument failed and the argument is preceded by an argument starting with `-`, try removing
+      // that as well. E.g. removing `-F` followed by a search path.
+      if requestInfo.compilerArgs[safe: argumentIndexToRemove - numberOfArgumentsToRemove]?.hasPrefix("-") ?? false {
         numberOfArgumentsToRemove += 1
-      }
 
-      // If the argument is preceded by -Xswiftc or -Xcxx, we need to remove the `-X` flag as well.
-      if argumentIndexToRemove - numberOfArgumentsToRemove >= 0
-        && requestInfo.compilerArgs[argumentIndexToRemove - numberOfArgumentsToRemove].hasPrefix("-X")
-      {
-        numberOfArgumentsToRemove += 1
+        // If the argument is preceded by -Xswiftc or -Xcxx, we need to remove the `-X` flag as well.
+        if requestInfo.compilerArgs[safe: argumentIndexToRemove - numberOfArgumentsToRemove]?.hasPrefix("-X") ?? false {
+          numberOfArgumentsToRemove += 1
+        }
+
+        let rangeToRemove = (argumentIndexToRemove - numberOfArgumentsToRemove + 1)...argumentIndexToRemove
+        if let reduced = try await tryRemoving(rangeToRemove, from: requestInfo) {
+          requestInfo = reduced
+          argumentIndexToRemove -= numberOfArgumentsToRemove
+          continue
+        }
       }
 
-      if let reduced = try await tryRemoving(
-        (argumentIndexToRemove - numberOfArgumentsToRemove + 1)...argumentIndexToRemove,
-        from: requestInfo
-      ) {
-        requestInfo = reduced
-        argumentIndexToRemove -= numberOfArgumentsToRemove
-        continue
-      }
-      argumentIndexToRemove -= 1
+      argumentIndexToRemove -= simultaneousRemove
     }
 
     return requestInfo
@@ -111,16 +117,28 @@ fileprivate class CommandLineArgumentReducer {
     _ argumentsToRemove: ClosedRange<Int>,
     from requestInfo: RequestInfo
   ) async throws -> RequestInfo? {
+    logger.debug("Try removing the following compiler arguments:\n\(requestInfo.compilerArgs[argumentsToRemove])")
     var reducedRequestInfo = requestInfo
     reducedRequestInfo.compilerArgs.removeSubrange(argumentsToRemove)
 
     let result = try await sourcekitdExecutor.run(request: reducedRequestInfo)
     if case .reproducesIssue = result {
-      logSuccessfulReduction(reducedRequestInfo)
+      logger.debug("Reduction successful")
       return reducedRequestInfo
     } else {
       // The reduced request did not crash. We did not find a reduced test case, so return `nil`.
+      logger.debug("Reduction did not reproduce the issue")
+      return nil
+    }
+  }
+}
+
+fileprivate extension Array {
+  /// Access index in the array if it's in bounds or return `nil` if `index` is outside of the array's bounds.
+  subscript(safe index: Int) -> Element? {
+    if index < 0 || index >= count {
       return nil
     }
+    return self[index]
   }
 }