Rebuild if processing options changed

Author: ting-yuan

compiler-plugin/src/main/kotlin/com/google/devtools/ksp/Incremental.kt

@@ -336,13 +336,34 @@ class IncrementalContext(
         logFile.appendText("\nDirty / All: $percentage%\n\n")
     }
 
+    private val processingOptionsFile = File(options.cachesDir, "processing.options")
+    private val processingOptionsString: String by lazy {
+        StringBuilder().apply {
+            options.processingOptions.toSortedMap().forEach {
+                append("${it.key}: ${it.value}\n")
+            }
+        }.toString()
+    }
+
+    private val isProcessingOptionsChanged: Boolean by lazy {
+        if (processingOptionsFile.exists() && processingOptionsFile.isFile) {
+            val fileContents = processingOptionsFile.readText()
+            processingOptionsString == fileContents
+        } else {
+            true
+        }
+    }
+
     // Beware: no side-effects here; Caches should only be touched in updateCaches.
     fun calcDirtyFiles(): Collection<KSFile> {
         if (!isIncremental) {
             cleanIncrementalCache()
             return ksFiles
         }
 
+        if (isProcessingOptionsChanged)
+            rebuild = true
+
         if (!rebuild) {
             val dirtyFilesByDeps = calcDirtySetByDeps()
 
@@ -415,10 +436,16 @@ class IncrementalContext(
         }
     }
 
+    fun updateProcessingOptions() {
+        if (isProcessingOptionsChanged)
+            processingOptionsFile.writeText(processingOptionsString)
+    }
+
     // TODO: Don't do anything if processing failed.
     private fun updateCaches(dirtyFiles: Collection<File>, outputs: Set<File>, sourceToOutputs: Map<File, Set<File>>) {
         updateSourceToOutputs(dirtyFiles, outputs, sourceToOutputs)
         updateLookupCache(dirtyFiles)
+        updateProcessingOptions()
 
         // Update symbolsMap
         if (!rebuild) {