Add comments for generators about data/inline class (in psi2ir and fir2ir) and annotations (fir2ir).

compiler/backend-common/src/org/jetbrains/kotlin/backend/common/DataClassMethodGenerator.kt

@@ -16,17 +16,11 @@
 
 package org.jetbrains.kotlin.backend.common
 
-import org.jetbrains.kotlin.backend.common.CodegenUtil.getMemberToGenerate
-import org.jetbrains.kotlin.builtins.KotlinBuiltIns
-import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
-import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
-import org.jetbrains.kotlin.psi.KtClass
 import org.jetbrains.kotlin.psi.KtClassOrObject
 import org.jetbrains.kotlin.psi.KtParameter
 import org.jetbrains.kotlin.resolve.BindingContext
-import org.jetbrains.kotlin.resolve.BindingContextUtils
 
 /**
  * A platform-independent logic for generating data class synthetic methods.

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/AnnotationGenerator.kt

@@ -15,6 +15,14 @@ import org.jetbrains.kotlin.ir.expressions.IrConstructorCall
 import org.jetbrains.kotlin.ir.util.isPropertyField
 import org.jetbrains.kotlin.ir.util.isSetter
 
+/**
+ * A generator that converts annotations in [FirAnnotationContainer] to annotations in [IrMutableAnnotationContainer].
+ *
+ * In general, annotations are bound to the target in the beginning, i.e., clearly targeted at source level. But, there are some cases that
+ * need special handling: [AnnotationUseSiteTarget]. In particular, [FirProperty] contains all annotations associated with that property,
+ * whose targets may vary. After all the necessary pieces of IR elements, e.g., backing field, are ready, this generator splits those
+ * annotations to the specified targets.
+ */
 internal class AnnotationGenerator(private val visitor: Fir2IrVisitor) {
 
     fun generate(irContainer: IrMutableAnnotationContainer, firContainer: FirAnnotationContainer) {

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/DataClassMembersGenerator.kt

@@ -42,6 +42,14 @@ import org.jetbrains.kotlin.ir.util.defaultType
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
 
+/**
+ * A generator that generates synthetic members of data class as well as part of inline class.
+ *
+ * This one uses [DataClassMembersGenerator] to generate function bodies, shared with the counterpart in psi. But, there are two main
+ * differences. Unlike the counterpart in psi, which uses descriptor-based logic to determine which members to synthesize, this one uses
+ * fir own logic that traverses class hierarchies in fir elements. Also, this one creates and passes IR elements, instead of providing how
+ * to declare them, to [DataClassMembersGenerator].
+ */
 class DataClassMembersGenerator(val components: Fir2IrComponents) {
 
     fun generateInlineClassMembers(klass: FirClass<*>, irClass: IrClass): List<Name> =

compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/generators/DataClassMembersGenerator.kt

@@ -30,6 +30,12 @@ import org.jetbrains.kotlin.psi.psiUtil.startOffset
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.DescriptorToSourceUtils
 
+/**
+ * A generator that generates synthetic members of data class as well as part of inline class.
+ *
+ * This one uses [DataClassMethodGenerator] to determine which members are needed to generate; uses [DataClassMembersGenerator] to generate
+ * function bodies; and provides ways to declare functions or parameters based on descriptors and binding context.
+ */
 class DataClassMembersGenerator(
     declarationGenerator: DeclarationGenerator
 ) : DeclarationGeneratorExtension(declarationGenerator) {

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DataClassMembersGenerator.kt

@@ -27,6 +27,12 @@ import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
 import org.jetbrains.kotlin.types.isNullable
 import org.jetbrains.kotlin.types.typeUtil.representativeUpperBound
 
+/**
+ * A platform-, frontend-independent logic for generating synthetic members of data class: equals, hashCode, toString, componentN, and copy.
+ * Different front-ends may need to define how to declare functions, parameters, etc., or simply provide predefined ones.
+ *
+ * Generating synthetic members of inline class can use this as well, in particular, members from Any: equals, hashCode, and toString.
+ */
 abstract class DataClassMembersGenerator(
     val context: IrGeneratorContext,
     val symbolTable: SymbolTable,