KT-45777: Add debug log messages for classpath snapshot feature

Also clean up classpath snapshot shrinking a bit to make it clearer. ^KT-45777 In Progress
2022-03-22 23:05:16 +00:00
parent 1d1c6d5e0b
commit d70dbf3146
13 changed files with 236 additions and 125 deletions
@@ -6,6 +6,7 @@
 package org.jetbrains.kotlin.build.report

 import org.jetbrains.kotlin.build.report.metrics.BuildMetricsReporter
+import org.jetbrains.kotlin.build.report.metrics.DoNothingBuildMetricsReporter
 import org.jetbrains.kotlin.build.report.metrics.RemoteBuildMetricsReporter

 open class BuildReporter(
@@ -22,3 +23,5 @@ class RemoteBuildReporter(
        buildMetricsReporter.flush()
    }
 }
+
+object DoNothingBuildReporter : BuildReporter(DoNothingICReporter, DoNothingBuildMetricsReporter)
@@ -18,4 +18,11 @@ interface ICReporter {
    fun reportMarkDirty(affectedFiles: Iterable<File>, reason: String)
 }

-
+object DoNothingICReporter : ICReporter {
+    override fun report(message: () -> String) {}
+    override fun reportVerbose(message: () -> String) {}
+    override fun reportCompileIteration(incremental: Boolean, sourceFiles: Collection<File>, exitCode: ExitCode) {}
+    override fun reportMarkDirtyClass(affectedFiles: Iterable<File>, classFqName: String) {}
+    override fun reportMarkDirtyMember(affectedFiles: Iterable<File>, scope: String, name: String) {}
+    override fun reportMarkDirty(affectedFiles: Iterable<File>, reason: String) {}
+}
@@ -17,8 +17,9 @@ enum class BuildPerformanceMetric(val parent: BuildPerformanceMetric? = null, va

    // Metrics for the `kotlin.incremental.useClasspathSnapshot` feature
    CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT(parent = null, "Number of times 'ClasspathEntrySnapshotTransform' ran", type = SizeMetricType.NUMBER),
-        JAR_CLASSPATH_ENTRY_SIZE(parent = CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT, "Size of classpath entry (if it's a jar)", type = SizeMetricType.BYTES),
-        CLASSPATH_ENTRY_SNAPSHOT_SIZE(parent = CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT, "Size of classpath entry (directory or jar)'s snapshot", type = SizeMetricType.BYTES),
+        JAR_CLASSPATH_ENTRY_SIZE(parent = CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT, "Size of jar classpath entry", type = SizeMetricType.BYTES),
+        JAR_CLASSPATH_ENTRY_SNAPSHOT_SIZE(parent = CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT, "Size of jar classpath entry's snapshot", type = SizeMetricType.BYTES),
+        DIRECTORY_CLASSPATH_ENTRY_SNAPSHOT_SIZE(parent = CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT, "Size of directory classpath entry's snapshot", type = SizeMetricType.BYTES),
    SHRINK_AND_SAVE_CLASSPATH_SNAPSHOT_EXECUTION_COUNT(parent = null, "Number of times classpath snapshot is shrunk and saved after compilation", type = SizeMetricType.NUMBER),
        CLASSPATH_ENTRY_COUNT(parent = SHRINK_AND_SAVE_CLASSPATH_SNAPSHOT_EXECUTION_COUNT, "Number of classpath entries", type = SizeMetricType.NUMBER),
        CLASSPATH_SNAPSHOT_SIZE(parent = SHRINK_AND_SAVE_CLASSPATH_SNAPSHOT_EXECUTION_COUNT, "Size of classpath snapshot", type = SizeMetricType.BYTES),
@@ -51,11 +51,11 @@ enum class BuildTime(val parent: BuildTime? = null, val readableString: String)
                COMPILATION_ROUND(INCREMENTAL_COMPILATION_DAEMON, "Sources compilation round"),
                IC_WRITE_HISTORY_FILE(INCREMENTAL_COMPILATION_DAEMON, "Write history file"),
                SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION(INCREMENTAL_COMPILATION_DAEMON, "Shrink and save current classpath snapshot after compilation"),
-                    INCREMENTAL_LOAD_SHRUNK_PREVIOUS_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Incremental shrinking - Load shrunk previous classpath snapshot"),
-                    INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Incremental shrinking - Load current classpath snapshot"),
-                    INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Incremental shrinking - Shrink current classpath snapshot"),
-                    NON_INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Non-incremental shrinking - Load current classpath snapshot"),
-                    NON_INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Non-incremental shrinking - Shrink current classpath snapshot"),
+                    INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Shrink current classpath snapshot incrementally"),
+                        INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT(INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT, "Load current classpath snapshot"),
+                        INCREMENTAL_LOAD_SHRUNK_CURRENT_CLASSPATH_SNAPSHOT_AGAINST_PREVIOUS_LOOKUPS(INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT, "Load shrunk current classpath snapshot against previous lookups"),
+                    NON_INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Shrink current classpath snapshot non-incrementally"),
+                        NON_INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT(NON_INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT, "Load current classpath snapshot"),
                    SAVE_SHRUNK_CURRENT_CLASSPATH_SNAPSHOT(SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION, "Save shrunk current classpath snapshot"),
    COMPILER_PERFORMANCE(readableString = "Compiler time"),
        COMPILER_INITIALIZATION(COMPILER_PERFORMANCE, "Compiler initialization time"),
@@ -86,16 +86,16 @@ class IncrementalCompilationOptions(

    override fun toString(): String {
        return "IncrementalCompilationOptions(" +
-               "super=${super.toString()}, " +
-               "areFileChangesKnown=$areFileChangesKnown, " +
-               "modifiedFiles=$modifiedFiles, " +
-               "deletedFiles=$deletedFiles, " +
-               "classpathChanges=$classpathChanges, " +
-               "workingDir=$workingDir, " +
-               "multiModuleICSettings=$multiModuleICSettings, " +
-               "usePreciseJavaTracking=$usePreciseJavaTracking" +
-               "outputFiles=$outputFiles" +
-               ")"
+                "super=${super.toString()}, " +
+                "areFileChangesKnown=$areFileChangesKnown, " +
+                "modifiedFiles=$modifiedFiles, " +
+                "deletedFiles=$deletedFiles, " +
+                "classpathChanges=${classpathChanges::class.simpleName}, " +
+                "workingDir=$workingDir, " +
+                "multiModuleICSettings=$multiModuleICSettings, " +
+                "usePreciseJavaTracking=$usePreciseJavaTracking" +
+                "outputFiles=$outputFiles" +
+                ")"
    }
 }

@@ -51,9 +51,11 @@ import org.jetbrains.kotlin.incremental.ClasspathChanges.ClasspathSnapshotEnable
 import org.jetbrains.kotlin.incremental.ClasspathChanges.ClasspathSnapshotEnabled.NotAvailableDueToMissingClasspathSnapshot
 import org.jetbrains.kotlin.incremental.ClasspathChanges.ClasspathSnapshotEnabled.NotAvailableForNonIncrementalRun
 import org.jetbrains.kotlin.incremental.ClasspathChanges.NotAvailableForJSCompiler
-import org.jetbrains.kotlin.incremental.classpathDiff.*
-import org.jetbrains.kotlin.incremental.classpathDiff.ClasspathChangesComputer.computeChangedAndImpactedSet
-import org.jetbrains.kotlin.incremental.classpathDiff.ClasspathSnapshotShrinker.shrinkClasspath
+import org.jetbrains.kotlin.incremental.classpathDiff.AccessibleClassSnapshot
+import org.jetbrains.kotlin.incremental.classpathDiff.ClasspathChangesComputer.computeClasspathChanges
+import org.jetbrains.kotlin.incremental.classpathDiff.ClasspathSnapshotBuildReporter
+import org.jetbrains.kotlin.incremental.classpathDiff.shrinkAndSaveClasspathSnapshot
+import org.jetbrains.kotlin.incremental.classpathDiff.toChangesEither
 import org.jetbrains.kotlin.incremental.components.ExpectActualTracker
 import org.jetbrains.kotlin.incremental.components.LookupTracker
 import org.jetbrains.kotlin.incremental.multiproject.EmptyModulesApiHistory
@@ -235,32 +237,24 @@ class IncrementalJvmCompilerRunner(
        val dirtyFiles = DirtyFilesContainer(caches, reporter, kotlinSourceFilesExtensions)
        initDirtyFiles(dirtyFiles, changedFiles)

+        reporter.reportVerbose { "Classpath changes info passed from Gradle task: ${classpathChanges::class.simpleName}" }
        val classpathChanges = when (classpathChanges) {
            // Note: classpathChanges is deserialized, so they are no longer singleton objects and need to be compared using `is` (not `==`)
            is NoChanges -> ChangesEither.Known(emptySet(), emptySet())
            is ToBeComputedByIncrementalCompiler -> reporter.measure(BuildTime.COMPUTE_CLASSPATH_CHANGES) {
-                check(currentClasspathSnapshot == null)
-                currentClasspathSnapshot = reporter.measure(BuildTime.LOAD_CURRENT_CLASSPATH_SNAPSHOT) {
-                    val classpathSnapshot =
-                        CachedClasspathSnapshotSerializer.load(classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles)
-                    reporter.measure(BuildTime.REMOVE_DUPLICATE_CLASSES) {
-                        classpathSnapshot.removeDuplicateAndInaccessibleClasses()
+                val storeCurrentClasspathSnapshotForReuse =
+                    { currentClasspathSnapshotArg: List<AccessibleClassSnapshot>,
+                      shrunkCurrentClasspathAgainstPreviousLookupsArg: List<AccessibleClassSnapshot> ->
+                        check(currentClasspathSnapshot == null)
+                        check(shrunkCurrentClasspathAgainstPreviousLookups == null)
+                        currentClasspathSnapshot = currentClasspathSnapshotArg
+                        shrunkCurrentClasspathAgainstPreviousLookups = shrunkCurrentClasspathAgainstPreviousLookupsArg
                    }
-                }
-                check(shrunkCurrentClasspathAgainstPreviousLookups == null)
-                shrunkCurrentClasspathAgainstPreviousLookups = reporter.measure(BuildTime.SHRINK_CURRENT_CLASSPATH_SNAPSHOT) {
-                    shrinkClasspath(
-                        currentClasspathSnapshot!!, caches.lookupCache,
-                        ClasspathSnapshotShrinker.MetricsReporter(
-                            reporter,
-                            BuildTime.GET_LOOKUP_SYMBOLS, BuildTime.FIND_REFERENCED_CLASSES, BuildTime.FIND_TRANSITIVELY_REFERENCED_CLASSES
-                        )
-                    )
-                }
-                computeChangedAndImpactedSet(
-                    shrunkCurrentClasspathAgainstPreviousLookups!!,
-                    classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile,
-                    reporter
+                computeClasspathChanges(
+                    classpathChanges.classpathSnapshotFiles,
+                    caches.lookupCache,
+                    storeCurrentClasspathSnapshotForReuse,
+                    ClasspathSnapshotBuildReporter(reporter)
                ).toChangesEither()
            }
            is NotAvailableDueToMissingClasspathSnapshot -> ChangesEither.Unknown(BuildAttribute.CLASSPATH_SNAPSHOT_NOT_FOUND)
@@ -491,7 +485,7 @@ class IncrementalJvmCompilerRunner(
            reporter.measure(BuildTime.SHRINK_AND_SAVE_CURRENT_CLASSPATH_SNAPSHOT_AFTER_COMPILATION) {
                shrinkAndSaveClasspathSnapshot(
                    classpathChanges, caches.lookupCache, currentClasspathSnapshot, shrunkCurrentClasspathAgainstPreviousLookups,
-                    reporter
+                    ClasspathSnapshotBuildReporter(reporter)
                )
            }
        }
@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.build.report.metrics.BuildMetricsReporter
 import org.jetbrains.kotlin.build.report.metrics.BuildTime
 import org.jetbrains.kotlin.build.report.metrics.measure
 import org.jetbrains.kotlin.incremental.*
+import org.jetbrains.kotlin.incremental.classpathDiff.ClasspathSnapshotShrinker.shrinkClasspath
 import org.jetbrains.kotlin.incremental.classpathDiff.ImpactAnalysis.computeImpactedSetInclusive
 import org.jetbrains.kotlin.incremental.storage.FileToCanonicalPathConverter
 import org.jetbrains.kotlin.incremental.storage.ListExternalizer
@@ -17,28 +18,53 @@ import org.jetbrains.kotlin.incremental.storage.loadFromFile
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.resolve.jvm.JvmClassName
 import org.jetbrains.kotlin.resolve.sam.SAM_LOOKUP_NAME
-import java.io.File
 import java.util.*

 /** Computes changes between two [ClasspathSnapshot]s .*/
 object ClasspathChangesComputer {

    /**
-     * Computes changes between the current and previous shrunk [ClasspathSnapshot]s, plus unchanged elements that are impacted by the
-     * changes.
+     * Computes changes between the current and previous classpath, plus unchanged elements that are impacted by the changes.
     *
-     * NOTE: The original classpath may contain duplicate classes, but the shrunk classpath must not contain duplicate classes.
+     * NOTE: We shrink the classpath first before comparing them. The original classpath may contain duplicate classes, but the shrunk
+     * classpath must not contain duplicate classes.
     */
-    fun computeChangedAndImpactedSet(
-        shrunkCurrentClasspathSnapshot: List<AccessibleClassSnapshot>,
-        shrunkPreviousClasspathSnapshotFile: File,
-        metrics: BuildMetricsReporter
+    fun computeClasspathChanges(
+        classpathSnapshotFiles: ClasspathSnapshotFiles,
+        lookupStorage: LookupStorage,
+        storeCurrentClasspathSnapshotForReuse: (currentClasspathSnapshot: List<AccessibleClassSnapshot>, shrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>) -> Unit,
+        reporter: ClasspathSnapshotBuildReporter
    ): ProgramSymbolSet {
-        val shrunkPreviousClasspathSnapshot = metrics.measure(BuildTime.LOAD_SHRUNK_PREVIOUS_CLASSPATH_SNAPSHOT) {
-            ListExternalizer(AccessibleClassSnapshotExternalizer).loadFromFile(shrunkPreviousClasspathSnapshotFile)
+        val currentClasspathSnapshot = reporter.measure(BuildTime.LOAD_CURRENT_CLASSPATH_SNAPSHOT) {
+            val classpathSnapshot = CachedClasspathSnapshotSerializer.load(classpathSnapshotFiles.currentClasspathEntrySnapshotFiles)
+            reporter.measure(BuildTime.REMOVE_DUPLICATE_CLASSES) {
+                classpathSnapshot.removeDuplicateAndInaccessibleClasses()
+            }
        }
-        return metrics.measure(BuildTime.COMPUTE_CHANGED_AND_IMPACTED_SET) {
-            computeChangedAndImpactedSet(shrunkCurrentClasspathSnapshot, shrunkPreviousClasspathSnapshot, metrics)
+        val shrunkCurrentClasspathAgainstPreviousLookups = reporter.measure(BuildTime.SHRINK_CURRENT_CLASSPATH_SNAPSHOT) {
+            shrinkClasspath(
+                currentClasspathSnapshot, lookupStorage,
+                ClasspathSnapshotShrinker.MetricsReporter(
+                    reporter,
+                    BuildTime.GET_LOOKUP_SYMBOLS, BuildTime.FIND_REFERENCED_CLASSES, BuildTime.FIND_TRANSITIVELY_REFERENCED_CLASSES
+                )
+            )
+        }
+        reporter.reportVerbose {
+            "Shrunk current classpath snapshot for diffing," +
+                    " retained ${shrunkCurrentClasspathAgainstPreviousLookups.size} / ${currentClasspathSnapshot.size} classes"
+        }
+        storeCurrentClasspathSnapshotForReuse(currentClasspathSnapshot, shrunkCurrentClasspathAgainstPreviousLookups)
+
+        val shrunkPreviousClasspathSnapshot = reporter.measure(BuildTime.LOAD_SHRUNK_PREVIOUS_CLASSPATH_SNAPSHOT) {
+            ListExternalizer(AccessibleClassSnapshotExternalizer).loadFromFile(classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile)
+        }
+        reporter.reportVerbose {
+            "Loaded shrunk previous classpath snapshot for diffing, found ${shrunkPreviousClasspathSnapshot.size} classes"
+        }
+
+        return reporter.measure(BuildTime.COMPUTE_CHANGED_AND_IMPACTED_SET) {
+            computeChangedAndImpactedSet(shrunkCurrentClasspathAgainstPreviousLookups, shrunkPreviousClasspathSnapshot, reporter)
        }
    }

@@ -50,7 +76,7 @@ object ClasspathChangesComputer {
    fun computeChangedAndImpactedSet(
        currentClassSnapshots: List<AccessibleClassSnapshot>,
        previousClassSnapshots: List<AccessibleClassSnapshot>,
-        metrics: BuildMetricsReporter
+        reporter: ClasspathSnapshotBuildReporter
    ): ProgramSymbolSet {
        val currentClasses: Map<ClassId, AccessibleClassSnapshot> = currentClassSnapshots.associateBy { it.classId }
        val previousClasses: Map<ClassId, AccessibleClassSnapshot> = previousClassSnapshots.associateBy { it.classId }
@@ -69,15 +95,16 @@ object ClasspathChangesComputer {
            } else null
        }

-        val classChanges = metrics.measure(BuildTime.COMPUTE_CLASS_CHANGES) {
-            computeClassChanges(changedCurrentClasses, changedPreviousClasses, metrics)
+        val changedSet = reporter.measure(BuildTime.COMPUTE_CLASS_CHANGES) {
+            computeClassChanges(changedCurrentClasses, changedPreviousClasses, reporter)
+        }
+        reporter.reportVerboseWithLimit { "Changed set = ${changedSet.toDebugString()}" }
+
+        if (changedSet.isEmpty()) {
+            return changedSet
        }

-        if (classChanges.isEmpty()) {
-            return classChanges
-        }
-
-        return metrics.measure(BuildTime.COMPUTE_IMPACTED_SET) {
+        val changedAndImpactedSet = reporter.measure(BuildTime.COMPUTE_IMPACTED_SET) {
            // Note that changes may contain added symbols (they can also impact recompilation -- see examples in JavaClassChangesComputer).
            // So ideally, the result should be:
            //     computeImpactedSetInclusive(changes = changesOnPreviousClasspath, allClasses = classesOnPreviousClasspath) +
@@ -88,10 +115,16 @@ object ClasspathChangesComputer {
            // Note: `allClasses` may contain overlapping ClassIds, but it won't be an issue. Also, we will replace
            // classesOnCurrentClasspath with changedClassesOnCurrentClasspath to avoid listing unchanged classes twice.
            computeImpactedSetInclusive(
-                changes = classChanges,
+                changes = changedSet,
                allClasses = (previousClassSnapshots.asSequence() + changedCurrentClasses.asSequence()).asIterable()
            )
        }
+        reporter.reportVerboseWithLimit {
+            "Impacted classes = " +
+                    (changedAndImpactedSet.run { classes + classMembers.keys } - changedSet.run { classes + classMembers.keys })
+        }
+
+        return changedAndImpactedSet
    }

    /**
@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.incremental.classpathDiff
+
+import org.jetbrains.kotlin.build.report.BuildReporter
+import org.jetbrains.kotlin.build.report.ICReporter
+import org.jetbrains.kotlin.build.report.metrics.BuildMetricsReporter
+
+class ClasspathSnapshotBuildReporter(private val buildReporter: BuildReporter) :
+    ICReporter by buildReporter, BuildMetricsReporter by buildReporter {
+
+    override fun reportVerbose(message: () -> String) {
+        buildReporter.reportVerbose { "[ClasspathSnapshot] ${message()}" }
+    }
+
+    fun reportVerboseWithLimit(maxLength: Int = 1000, message: () -> String) {
+        reportVerbose {
+            message().let {
+                if (it.length > maxLength) {
+                    it.substring(0, maxLength) + "... (string too long, showing $maxLength / ${it.length} chars)"
+                } else it
+            }
+        }
+    }
+}
@@ -174,27 +174,36 @@ private fun ClasspathSnapshot.getNonDuplicateClassSnapshots(): List<ClassSnapsho

 /** Used by [shrinkAndSaveClasspathSnapshot]. */
 private sealed class ShrinkMode {
-    object NoChanges : ShrinkMode()
+    object UnchangedLookupsUnchangedClasspath : ShrinkMode()

-    class IncrementalNoNewLookups(
-        val shrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>,
-    ) : ShrinkMode()
-
-    class Incremental(
+    class UnchangedLookupsChangedClasspath(
        val currentClasspathSnapshot: List<AccessibleClassSnapshot>,
-        val shrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>,
-        val addedLookupSymbols: Set<LookupSymbolKey>
+        val shrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>
    ) : ShrinkMode()

+    sealed class ChangedLookups : ShrinkMode() {
+        abstract val addedLookupSymbols: Set<LookupSymbolKey>
+    }
+
+    class ChangedLookupsUnchangedClasspath(
+        override val addedLookupSymbols: Set<LookupSymbolKey>
+    ) : ChangedLookups()
+
+    class ChangedLookupsChangedClasspath(
+        override val addedLookupSymbols: Set<LookupSymbolKey>,
+        val currentClasspathSnapshot: List<AccessibleClassSnapshot>,
+        val shrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>
+    ) : ChangedLookups()
+
    object NonIncremental : ShrinkMode()
 }

 internal fun shrinkAndSaveClasspathSnapshot(
    classpathChanges: ClasspathChanges.ClasspathSnapshotEnabled,
    lookupStorage: LookupStorage,
-    currentClasspathSnapshot: List<AccessibleClassSnapshot>?, // Not null iff classpathChanges is ToBeComputedByIncrementalCompiler
-    shrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>?, // Same as above
-    metrics: BuildMetricsReporter
+    precomputedCurrentClasspathSnapshot: List<AccessibleClassSnapshot>?, // Not null iff classpathChanges is ToBeComputedByIncrementalCompiler
+    precomputedShrunkCurrentClasspathAgainstPreviousLookups: List<AccessibleClassSnapshot>?, // Not null iff classpathChanges is ToBeComputedByIncrementalCompiler
+    reporter: ClasspathSnapshotBuildReporter
 ) {
    // In the following, we'll try to shrink the classpath snapshot incrementally when possible.
    // For incremental shrinking, we currently use only lookupStorage.addedLookupSymbols, not lookupStorage.removedLookupSymbols. It is
@@ -204,72 +213,94 @@ internal fun shrinkAndSaveClasspathSnapshot(
        is NoChanges -> {
            val addedLookupSymbols = lookupStorage.addedLookupSymbols
            if (addedLookupSymbols.isEmpty()) {
-                ShrinkMode.NoChanges
+                ShrinkMode.UnchangedLookupsUnchangedClasspath
            } else {
-                val shrunkPreviousClasspathAgainstPreviousLookups =
-                    metrics.measure(BuildTime.INCREMENTAL_LOAD_SHRUNK_PREVIOUS_CLASSPATH_SNAPSHOT) {
-                        ListExternalizer(AccessibleClassSnapshotExternalizer)
-                            .loadFromFile(classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile)
-                    }
-                ShrinkMode.Incremental(
-                    currentClasspathSnapshot = metrics.measure(BuildTime.INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT) {
-                        CachedClasspathSnapshotSerializer
-                            .load(classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles)
-                            .removeDuplicateAndInaccessibleClasses()
-                    },
-                    // In the current case, there are no classpath changes, so
-                    // shrunk[*Current*]ClasspathAgainstPreviousLookups == shrunk[*Previous*]ClasspathAgainstPreviousLookups
-                    shrunkCurrentClasspathAgainstPreviousLookups = shrunkPreviousClasspathAgainstPreviousLookups,
-                    addedLookupSymbols = addedLookupSymbols
-                )
+                ShrinkMode.ChangedLookupsUnchangedClasspath(addedLookupSymbols)
            }
        }
        is ToBeComputedByIncrementalCompiler -> {
            val addedLookupSymbols = lookupStorage.addedLookupSymbols
            if (addedLookupSymbols.isEmpty()) {
-                ShrinkMode.IncrementalNoNewLookups(shrunkCurrentClasspathAgainstPreviousLookups!!)
+                ShrinkMode.UnchangedLookupsChangedClasspath(
+                    precomputedCurrentClasspathSnapshot!!,
+                    precomputedShrunkCurrentClasspathAgainstPreviousLookups!!
+                )
            } else {
-                ShrinkMode.Incremental(currentClasspathSnapshot!!, shrunkCurrentClasspathAgainstPreviousLookups!!, addedLookupSymbols)
+                ShrinkMode.ChangedLookupsChangedClasspath(
+                    addedLookupSymbols,
+                    precomputedCurrentClasspathSnapshot!!,
+                    precomputedShrunkCurrentClasspathAgainstPreviousLookups!!
+                )
            }
        }
        is NotAvailableDueToMissingClasspathSnapshot, is NotAvailableForNonIncrementalRun -> ShrinkMode.NonIncremental
    }

    // Shrink current classpath against current lookups
-    val shrunkCurrentClasspath: List<AccessibleClassSnapshot>? = when (shrinkMode) {
-        is ShrinkMode.NoChanges -> null
-        is ShrinkMode.IncrementalNoNewLookups -> {
-            // There are no new lookups, so
-            // shrunkCurrentClasspathAgainst[*Current*]Lookups == shrunkCurrentClasspathAgainst[*Previous*]Lookups
-            shrinkMode.shrunkCurrentClasspathAgainstPreviousLookups
+    val (currentClasspath: List<AccessibleClassSnapshot>?, shrunkCurrentClasspath: List<AccessibleClassSnapshot>?) = when (shrinkMode) {
+        is ShrinkMode.UnchangedLookupsUnchangedClasspath -> {
+            // There are no changes in the lookups and classpath, so there will be no changes in the shrunk classpath snapshot compared to
+            // the previous run. Return null here as we don't need to compute this.
+            null to null
        }
-        is ShrinkMode.Incremental -> metrics.measure(BuildTime.INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT) {
-            val shrunkClasses = shrinkMode.shrunkCurrentClasspathAgainstPreviousLookups.mapTo(mutableSetOf()) { it.classId }
-            val notYetShrunkClasses = shrinkMode.currentClasspathSnapshot.filter { it.classId !in shrunkClasses }
-            val addedLookupSymbols = shrinkMode.addedLookupSymbols
-            val shrunkRemainingClassesAgainstNewLookups = shrinkClasses(notYetShrunkClasses, addedLookupSymbols)
+        is ShrinkMode.UnchangedLookupsChangedClasspath -> {
+            // There are no changes in the lookups, so
+            // shrunkCurrentClasspathAgainst[*Current*]Lookups == shrunkCurrentClasspathAgainst[*Previous*]Lookups
+            shrinkMode.currentClasspathSnapshot to shrinkMode.shrunkCurrentClasspathAgainstPreviousLookups
+        }
+        is ShrinkMode.ChangedLookups -> reporter.measure(BuildTime.INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT) {
+            // There are changes in the lookups, so we will shrink incrementally.
+            val currentClasspath = reporter.measure(BuildTime.INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT) {
+                when (shrinkMode) {
+                    is ShrinkMode.ChangedLookupsUnchangedClasspath ->
+                        CachedClasspathSnapshotSerializer
+                            .load(classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles)
+                            .removeDuplicateAndInaccessibleClasses()
+                    is ShrinkMode.ChangedLookupsChangedClasspath -> shrinkMode.currentClasspathSnapshot
+                }
+            }
+            val shrunkCurrentClasspathAgainstPreviousLookups =
+                reporter.measure(BuildTime.INCREMENTAL_LOAD_SHRUNK_CURRENT_CLASSPATH_SNAPSHOT_AGAINST_PREVIOUS_LOOKUPS) {
+                    when (shrinkMode) {
+                        is ShrinkMode.ChangedLookupsUnchangedClasspath -> {
+                            // There are no changes in the classpath, so
+                            // shrunk[*Current*]ClasspathAgainstPreviousLookups == shrunk[*Previous*]ClasspathAgainstPreviousLookups
+                            ListExternalizer(AccessibleClassSnapshotExternalizer)
+                                .loadFromFile(classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile)
+                        }
+                        is ShrinkMode.ChangedLookupsChangedClasspath -> shrinkMode.shrunkCurrentClasspathAgainstPreviousLookups
+                    }
+                }

-            shrinkMode.shrunkCurrentClasspathAgainstPreviousLookups + shrunkRemainingClassesAgainstNewLookups
+            val shrunkClasses = shrunkCurrentClasspathAgainstPreviousLookups.mapTo(mutableSetOf()) { it.classId }
+            val notYetShrunkClasses = currentClasspath.filter { it.classId !in shrunkClasses }
+            val shrunkRemainingClassesAgainstNewLookups = shrinkClasses(notYetShrunkClasses, shrinkMode.addedLookupSymbols)
+
+            val shrunkCurrentClasspath = shrunkCurrentClasspathAgainstPreviousLookups + shrunkRemainingClassesAgainstNewLookups
+            currentClasspath to shrunkCurrentClasspath
        }
        is ShrinkMode.NonIncremental -> {
-            val classpathSnapshot = metrics.measure(BuildTime.NON_INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT) {
-                CachedClasspathSnapshotSerializer
-                    .load(classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles)
-                    .removeDuplicateAndInaccessibleClasses()
-            }
-            metrics.measure(BuildTime.NON_INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT) {
-                shrinkClasspath(classpathSnapshot, lookupStorage)
+            // Changes in the lookups and classpath are not available, so we will shrink non-incrementally.
+            reporter.measure(BuildTime.NON_INCREMENTAL_SHRINK_CURRENT_CLASSPATH_SNAPSHOT) {
+                val currentClasspath = reporter.measure(BuildTime.NON_INCREMENTAL_LOAD_CURRENT_CLASSPATH_SNAPSHOT) {
+                    CachedClasspathSnapshotSerializer
+                        .load(classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles)
+                        .removeDuplicateAndInaccessibleClasses()
+                }
+                val shrunkCurrentClasspath = shrinkClasspath(currentClasspath, lookupStorage)
+                currentClasspath to shrunkCurrentClasspath
            }
        }
    }

-    if (shrinkMode == ShrinkMode.NoChanges) {
-        // There are no updates to the file so just check that it exists
-        check(classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile.exists()) {
+    if (shrinkMode == ShrinkMode.UnchangedLookupsUnchangedClasspath) {
+        // There are no changes in the lookups and classpath, so there will be no changes in the shrunk classpath snapshot compared to the
+        // previous run. Just double-check that the file still exists.
+        check(classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile.isFile) {
            "File '${classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile.path}' does not exist"
        }
    } else {
-        metrics.measure(BuildTime.SAVE_SHRUNK_CURRENT_CLASSPATH_SNAPSHOT) {
+        reporter.measure(BuildTime.SAVE_SHRUNK_CURRENT_CLASSPATH_SNAPSHOT) {
            ListExternalizer(AccessibleClassSnapshotExternalizer).saveToFile(
                classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile,
                shrunkCurrentClasspath!!
@@ -277,16 +308,23 @@ internal fun shrinkAndSaveClasspathSnapshot(
        }
    }

-    metrics.addMetric(BuildPerformanceMetric.SHRINK_AND_SAVE_CLASSPATH_SNAPSHOT_EXECUTION_COUNT, 1)
-    metrics.addMetric(
+    reporter.reportVerbose {
+        "Shrunk current classpath snapshot after compilation (shrink mode = ${shrinkMode::class.simpleName})" + when (shrinkMode) {
+            is ShrinkMode.UnchangedLookupsUnchangedClasspath -> ", no updates since previous run"
+            else -> ", retained ${shrunkCurrentClasspath!!.size} / ${currentClasspath!!.size} classes"
+        }
+    }
+
+    reporter.addMetric(BuildPerformanceMetric.SHRINK_AND_SAVE_CLASSPATH_SNAPSHOT_EXECUTION_COUNT, 1)
+    reporter.addMetric(
        BuildPerformanceMetric.CLASSPATH_ENTRY_COUNT,
        classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles.size.toLong()
    )
-    metrics.addMetric(
+    reporter.addMetric(
        BuildPerformanceMetric.CLASSPATH_SNAPSHOT_SIZE,
        classpathChanges.classpathSnapshotFiles.currentClasspathEntrySnapshotFiles.sumOf { it.length() }
    )
-    metrics.addMetric(
+    reporter.addMetric(
        BuildPerformanceMetric.SHRUNK_CLASSPATH_SNAPSHOT_SIZE,
        classpathChanges.classpathSnapshotFiles.shrunkPreviousClasspathSnapshotFile.length()
    )
@@ -58,6 +58,10 @@ class ProgramSymbolSet private constructor(
                    .flatMap { (packageFqName, memberNames) -> memberNames.asSequence().map { PackageMember(packageFqName, it) } }
    }

+    fun toDebugString(): String {
+        return "${ProgramSymbolSet::class.simpleName}(classes = $classes, classMembers = $classMembers, packageMembers = $packageMembers)"
+    }
+
    /**
     * Collects [ProgramSymbol]s and returns a [ProgramSymbolSet].
     *
@@ -5,7 +5,7 @@

 package org.jetbrains.kotlin.incremental.classpathDiff

-import org.jetbrains.kotlin.build.report.metrics.DoNothingBuildMetricsReporter
+import org.jetbrains.kotlin.build.report.DoNothingBuildReporter
 import org.jetbrains.kotlin.incremental.ChangesEither
 import org.jetbrains.kotlin.incremental.LookupSymbol
 import org.jetbrains.kotlin.incremental.classpathDiff.ClassSnapshotGranularity.CLASS_LEVEL
@@ -437,7 +437,7 @@ private fun computeClasspathChanges(
    return ClasspathChangesComputer.computeChangedAndImpactedSet(
        currentClasspathSnapshot.removeDuplicateAndInaccessibleClasses(),
        previousClasspathSnapshot.removeDuplicateAndInaccessibleClasses(),
-        DoNothingBuildMetricsReporter
+        ClasspathSnapshotBuildReporter(DoNothingBuildReporter)
    ).normalize()
 }

@@ -95,8 +95,11 @@ abstract class ClasspathEntrySnapshotTransform : TransformAction<ClasspathEntryS
            metrics.addMetric(BuildPerformanceMetric.CLASSPATH_ENTRY_SNAPSHOT_TRANSFORM_EXECUTION_COUNT, 1)
            if (classpathEntryInputDirOrJar.extension.equals("jar", ignoreCase = true)) {
                metrics.addMetric(BuildPerformanceMetric.JAR_CLASSPATH_ENTRY_SIZE, classpathEntryInputDirOrJar.length())
+                metrics.addMetric(BuildPerformanceMetric.JAR_CLASSPATH_ENTRY_SNAPSHOT_SIZE, snapshotOutputFile.length())
+            } else {
+                // Only compute the size of the snapshot, not the size of the input directory as walking the file tree has a small overhead
+                metrics.addMetric(BuildPerformanceMetric.DIRECTORY_CLASSPATH_ENTRY_SNAPSHOT_SIZE, snapshotOutputFile.length())
            }
-            metrics.addMetric(BuildPerformanceMetric.CLASSPATH_ENTRY_SNAPSHOT_SIZE, snapshotOutputFile.length())
        }
    }
 }
@@ -292,7 +292,7 @@ abstract class AbstractKotlinCompile<T : CommonCompilerArguments> @Inject constr
        private fun getKotlinBuildDir(task: T): Provider<Directory> =
            task.project.layout.buildDirectory.dir("$KOTLIN_BUILD_DIR_NAME/${task.name}")

-        protected fun getClasspathSnapshotDir(task: T): Provider<Directory> =
+        protected open fun getClasspathSnapshotDir(task: T): Provider<Directory> =
            getKotlinBuildDir(task).map { it.dir("classpath-snapshot") }
    }