If a build server doesn’t specify -index-store-path in the SourceKit options, add it during background indexing

Author: ahoppen

Sources/BuildSystemIntegration/FixedCompilationDatabaseBuildSystem.swift

@@ -24,10 +24,10 @@ import LanguageServerProtocol
 #endif
 
 func lastIndexStorePathArgument(in compilerArgs: [String]) -> String? {
-  for i in compilerArgs.indices.reversed() {
-    if compilerArgs[i] == "-index-store-path" && i + 1 < compilerArgs.count {
-      return compilerArgs[i + 1]
-    }
+  if let indexStorePathIndex = compilerArgs.lastIndex(of: "-index-store-path"),
+    indexStorePathIndex + 1 < compilerArgs.count
+  {
+    return compilerArgs[indexStorePathIndex + 1]
   }
   return nil
 }

Sources/SemanticIndex/UpdateIndexStoreTaskDescription.swift

@@ -311,7 +311,7 @@ package struct UpdateIndexStoreTaskDescription: IndexTaskDescription {
       return
     }
 
-    let args =
+    var args =
       try [swiftc.filePath] + buildSettings.compilerArguments + [
         "-index-file",
         "-index-file-path", uri.pseudoPath,
@@ -320,6 +320,25 @@ package struct UpdateIndexStoreTaskDescription: IndexTaskDescription {
         // Fake an output path so that we get a different unit file for every Swift file we background index
         "-index-unit-output-path", uri.pseudoPath + ".o",
       ]
+    guard let buildSystemIndexStorePath = await self.buildSystemManager.initializationData?.indexStorePath else {
+      struct NoIndexStorePathError: Error {}
+      throw NoIndexStorePathError()
+    }
+    if let indexStorePathIndex = args.lastIndex(of: "-index-store-path"), indexStorePathIndex + 1 < args.count {
+      let indexStorePath = args[indexStorePathIndex + 1]
+      if indexStorePath != buildSystemIndexStorePath {
+        logger.error(
+          """
+          Compiler arguments for \(uri) specify index store path \(indexStorePath) but build system specified an \
+          incompatible index store path \(buildSystemIndexStorePath). Overriding with the path specified by the build \
+          system.
+          """
+        )
+        args[indexStorePathIndex + 1] = buildSystemIndexStorePath
+      }
+    } else {
+      args += ["-index-store-path", buildSystemIndexStorePath]
+    }
 
     try await runIndexingProcess(
       indexFile: uri,