Enable eliding function bodies in header mode.

^KT-78422

Author: aviroop-123

compiler/fir/raw-fir/light-tree2fir/src/org/jetbrains/kotlin/fir/lightTree/converter/LightTreeRawFirDeclarationBuilder.kt

@@ -97,7 +97,7 @@ class LightTreeRawFirDeclarationBuilder(
                 }
                 IMPORT_LIST -> importList += convertImportDirectives(child)
                 CLASS -> firDeclarationList += convertClass(child)
-                FUN -> firDeclarationList += convertFunctionDeclaration(child) as FirDeclaration
+                FUN -> firDeclarationList += convertFunctionDeclaration(child, headerCompilationMode) as FirDeclaration
                 KtNodeTypes.PROPERTY -> firDeclarationList += convertPropertyDeclaration(child)
                 TYPEALIAS -> firDeclarationList += convertTypeAlias(child)
                 OBJECT_DECLARATION -> firDeclarationList += convertClass(child)
@@ -1923,7 +1923,7 @@ class LightTreeRawFirDeclarationBuilder(
     /**
      * @see org.jetbrains.kotlin.parsing.KotlinParsing.parseFunction
      */
-    fun convertFunctionDeclaration(functionDeclaration: LighterASTNode): FirStatement {
+    fun convertFunctionDeclaration(functionDeclaration: LighterASTNode, generateHeaders: Boolean = false): FirStatement {
         var modifiers: ModifierList? = null
         var identifier: String? = null
         var valueParametersList: LighterASTNode? = null
@@ -1940,6 +1940,8 @@ class LightTreeRawFirDeclarationBuilder(
             identifier = it.asText
         }
 
+        var headerMode = generateHeaders
+
         val isLocal = isCallableLocal(functionDeclaration) { getParent() }
         val functionSource = functionDeclaration.toFirSourceElement()
         val isAnonymousFunction = identifier == null && isLocal
@@ -1971,6 +1973,11 @@ class LightTreeRawFirDeclarationBuilder(
 
             val calculatedModifiers = modifiers ?: ModifierList()
 
+            if (calculatedModifiers.hasInline()) {
+                // We need to disable header mode for inline functions.
+                headerMode = false
+            }
+
             if (returnType == null) {
                 returnType =
                     if (block != null || !hasEqToken) implicitUnitType
@@ -2066,7 +2073,7 @@ class LightTreeRawFirDeclarationBuilder(
 
                     val allowLegacyContractDescription = outerContractDescription == null
                     val bodyWithContractDescription = withForcedLocalContext {
-                        convertFunctionBody(block, expression, allowLegacyContractDescription)
+                        convertFunctionBody(block, expression, allowLegacyContractDescription, headerMode)
                     }
                     this.body = bodyWithContractDescription.first
                     val contractDescription = outerContractDescription ?: bodyWithContractDescription.second
@@ -2103,11 +2110,12 @@ class LightTreeRawFirDeclarationBuilder(
     private fun convertFunctionBody(
         blockNode: LighterASTNode?,
         expression: LighterASTNode?,
-        allowLegacyContractDescription: Boolean
+        allowLegacyContractDescription: Boolean,
+        generateHeaders: Boolean = false,
     ): Pair<FirBlock?, FirContractDescription?> {
         return when {
             blockNode != null -> {
-                val block = convertBlock(blockNode)
+                val block = convertBlock(blockNode) // We might be able to process only the contract statement in the body.
                 val contractDescription = runIf(allowLegacyContractDescription) {
                     val blockSource = block.source
                     val diagnostic = when {
@@ -2117,7 +2125,11 @@ class LightTreeRawFirDeclarationBuilder(
                     }
                     processLegacyContractDescription(block, diagnostic)
                 }
-                block to contractDescription
+                if (generateHeaders) {
+                    null to contractDescription // We want to preserve the contract info when processing as headers.
+                } else {
+                    block to contractDescription
+                }
             }
             expression != null -> FirSingleExpressionBlock(
                 expressionConverter.getAsFirExpression<FirExpression>(expression, "Function has no body (but should)").toReturn()

compiler/ir/backend.jvm/codegen/src/org/jetbrains/kotlin/backend/jvm/codegen/ExpressionCodegen.kt

@@ -29,6 +29,7 @@ import org.jetbrains.kotlin.codegen.state.JvmBackendConfig
 import org.jetbrains.kotlin.config.JVMConfigurationKeys
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.config.LanguageVersionSettings
+import org.jetbrains.kotlin.config.headerCompilation
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.descriptors.VariableAccessorDescriptor
@@ -216,7 +217,7 @@ class ExpressionCodegen(
         mv.visitCode()
         val startLabel = markNewLabel()
         val info = BlockInfo()
-        if (state.classBuilderMode.generateBodies) {
+        if (state.classBuilderMode.generateBodies && !state.configuration.headerCompilation) {
             if (irFunction.isMultifileBridge()) {
                 // Multifile bridges need to have line number 1 to be filtered out by the intellij debugging filters.
                 mv.visitLineNumber(1, startLabel)