Fixes to KAPT classpath change detection

1) Fix tests to use canonical path for comparison because Mac was failing
2) Update current classpath snapshot only with the missing entries from the previous one
3) Clean-up code and style

plugins/kapt3/kapt3-base/src/org/jetbrains/kotlin/kapt3/base/KaptContext.kt

@@ -59,7 +59,7 @@ open class KaptContext(val options: KaptOptions, val withJdk: Boolean, val logge
         cacheManager = options.incrementalCache?.let {
             JavaClassCacheManager(it)
         }
-        if (options.processIncrementally) {
+        if (options.flags[KaptFlag.INCREMENTAL_APT]) {
             sourcesToReprocess =
                 cacheManager?.invalidateAndGetDirtyFiles(
                     options.changedFiles, options.classpathChanges

plugins/kapt3/kapt3-base/src/org/jetbrains/kotlin/kapt3/base/KaptOptions.kt

@@ -18,7 +18,6 @@ class KaptOptions(
     val compiledSources: List<File>,
     val incrementalCache: File?,
     val classpathChanges: List<String>,
-    val processIncrementally: Boolean,
 
     val sourcesOutputDir: File,
     val classesOutputDir: File,
@@ -52,7 +51,6 @@ class KaptOptions(
         var classesOutputDir: File? = null
         var stubsOutputDir: File? = null
         var incrementalDataOutputDir: File? = null
-        var processIncrementally: Boolean = false
 
         val processingClasspath: MutableList<File> = mutableListOf()
         val processors: MutableList<String> = mutableListOf()
@@ -75,7 +73,7 @@ class KaptOptions(
 
             return KaptOptions(
                 projectBaseDir, compileClasspath, javaSourceRoots,
-                changedFiles, compiledSources, incrementalCache, classpathChanges, processIncrementally,
+                changedFiles, compiledSources, incrementalCache, classpathChanges,
                 sourcesOutputDir, classesOutputDir, stubsOutputDir, incrementalDataOutputDir,
                 processingClasspath, processors, processingOptions, javacOptions, KaptFlags.fromSet(flags),
                 mode, detectMemoryLeaks
@@ -106,7 +104,9 @@ enum class KaptFlag(val description: String) {
     CORRECT_ERROR_TYPES("Correct error types"),
     MAP_DIAGNOSTIC_LOCATIONS("Map diagnostic locations"),
     STRICT("Strict mode"),
-    INCLUDE_COMPILE_CLASSPATH("Detect annotation processors in compile classpath");
+    INCLUDE_COMPILE_CLASSPATH("Detect annotation processors in compile classpath"),
+    INCREMENTAL_APT("Incremental annotation processing (apt mode)"),
+    ;
 }
 
 interface KaptSelector {
@@ -172,5 +172,4 @@ fun KaptOptions.logString(additionalInfo: String = "") = buildString {
     appendln("[incremental apt] Compiled sources directories: ${compiledSources.joinToString()}")
     appendln("[incremental apt] Cache directory for incremental compilation: $incrementalCache")
     appendln("[incremental apt] Changed classpath names: ${classpathChanges.joinToString()}")
-    appendln("[incremental apt] If processing incrementally: $processIncrementally")
 }

plugins/kapt3/kapt3-base/src/org/jetbrains/kotlin/kapt3/base/incremental/classStructureCache.kt

@@ -211,9 +211,7 @@ class SourceFileStructure(
 
     fun addMentionedConstant(containingClass: String, name: String) {
         if (!declaredTypes.contains(containingClass)) {
-            val names = mentionedConstants[containingClass] ?: HashSet()
-            names.add(name)
-            mentionedConstants[containingClass] = names
+            mentionedConstants.getOrPut(containingClass) { HashSet() }.add(name)
         }
     }
 }

plugins/kapt3/kapt3-base/test/org/jetbrains/kotlin/kapt3/base/incremental/IncrementalKaptTest.kt

@@ -5,6 +5,7 @@
 
 package org.jetbrains.kotlin.kapt.base.test.org.jetbrains.kotlin.kapt3.base.incremental
 
+import org.jetbrains.kotlin.base.kapt3.KaptFlag
 import org.jetbrains.kotlin.base.kapt3.KaptOptions
 import org.jetbrains.kotlin.base.kapt3.collectJavaSourceFiles
 import org.jetbrains.kotlin.kapt3.base.KaptContext
@@ -70,7 +71,7 @@ class IncrementalKaptTest {
             incrementalCache = incrementalCacheDir
             compiledSources.add(classesOutput)
             changedFiles.add(sourcesDir.resolve("User.java"))
-            processIncrementally = true
+            flags.add(KaptFlag.INCREMENTAL_APT)
         }.build()
 
         KaptContext(optionsForSecondRun, true, logger).use {
@@ -144,7 +145,7 @@ class IncrementalKaptTest {
             incrementalCache = incrementalCacheDir
             compiledSources.add(classesOutput)
             changedFiles.add(sourcesDir.resolve("User.java"))
-            processIncrementally = true
+            flags.add(KaptFlag.INCREMENTAL_APT)
         }.build()
 
         KaptContext(optionsForSecondRun, true, logger).use {

plugins/kapt3/kapt3-compiler/src/org/jetbrains/kotlin/kapt3/Kapt3Plugin.kt

@@ -101,7 +101,7 @@ class Kapt3CommandLineProcessor : CommandLineProcessor {
             COMPILED_SOURCES_DIR -> compiledSources.addAll(value.split(File.pathSeparator).map { File(it) })
             INCREMENTAL_CACHE -> incrementalCache = File(value)
             CLASSPATH_CHANGES -> classpathChanges.addAll(value.split(File.pathSeparator).map { it })
-            PROCESS_INCREMENTALLY -> processIncrementally = value.toBoolean()
+            PROCESS_INCREMENTALLY -> setFlag(KaptFlag.INCREMENTAL_APT, value)
 
             ANNOTATION_PROCESSOR_CLASSPATH_OPTION -> processingClasspath += File(value)
             ANNOTATION_PROCESSORS_OPTION -> processors.addAll(value.split(',').map { it.trim() }.filter { it.isNotEmpty() })