Handle bodies of interfaces with default method body.

^KT-78422

Author: aviroop-123

compiler/fir/analysis-tests/testData/resolve/headerMode/classDeclaration.fir.txt

@@ -21,7 +21,7 @@ FILE: classDeclaration.kt
 
     }
     public abstract interface B : R|kotlin/Any| {
-        public abstract fun funA(): R|kotlin/String|
+        public open fun funA(): R|kotlin/String|
 
         public abstract fun funB(): R|kotlin/String|
 

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

@@ -57,6 +57,7 @@ import org.jetbrains.kotlin.psi.stubs.elements.KtStubElementTypes
 import org.jetbrains.kotlin.util.getChildren
 import org.jetbrains.kotlin.utils.addToStdlib.runIf
 import org.jetbrains.kotlin.utils.addToStdlib.shouldNotBeCalled
+import org.jetbrains.kotlin.fir.declarations.utils.*
 
 class LightTreeRawFirDeclarationBuilder(
     session: FirSession,
@@ -701,6 +702,7 @@ class LightTreeRawFirDeclarationBuilder(
                 }
             }
         }.also {
+            it.isHeader = generateHeaders
             if (classNode.getParent()?.elementType == KtStubElementTypes.CLASS_BODY) {
                 it.initContainingClassForLocalAttr()
             }
@@ -2099,6 +2101,7 @@ class LightTreeRawFirDeclarationBuilder(
                 }
                 context.firFunctionTargets.removeLast()
             }.build().also {
+                it.isHeader = headerMode
                 target.bind(it)
                 fillDanglingConstraintsTo(firTypeParameters, typeConstraints, it)
             }
@@ -2138,7 +2141,8 @@ class LightTreeRawFirDeclarationBuilder(
                     processLegacyContractDescription(block, diagnostic)
                 }
                 if (generateHeaders) {
-                    null to contractDescription // We want to preserve the contract info when processing as headers.
+                    // Return an empty body, which will be removed after the status resolution.
+                    buildEmptyExpressionBlock() to contractDescription // We want to preserve the contract info when processing as headers.
                 } else {
                     block to contractDescription
                 }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirStatusResolveTransformer.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.fir.*
 import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.declarations.utils.componentFunctionSymbol
+import org.jetbrains.kotlin.fir.declarations.utils.isHeader
 import org.jetbrains.kotlin.fir.declarations.utils.isInlineOrValue
 import org.jetbrains.kotlin.fir.declarations.utils.visibility
 import org.jetbrains.kotlin.fir.expressions.FirBlock
@@ -426,6 +427,8 @@ abstract class AbstractFirStatusResolveTransformer(
             isLocal = false,
             overriddenFunctions.map { it.status as FirResolvedDeclarationStatus },
         )
+        // Once the modality is determined, we can remove the body.
+        if (simpleFunction.isHeader == true) simpleFunction.replaceBody(null)
 
         simpleFunction.transformStatus(this, resolvedStatus)
         transformDeclaration(simpleFunction, data) as FirStatement

compiler/fir/tree/src/org/jetbrains/kotlin/fir/declarations/utils/declarationAttributes.kt

@@ -41,6 +41,7 @@ private object IsDeserializedPropertyFromAnnotation : FirDeclarationDataKey()
 private object IsDelegatedProperty : FirDeclarationDataKey()
 private object LambdaArgumentHoldsInTruths : FirDeclarationDataKey()
 private object FileNameForPluginGeneratedCallable : FirDeclarationDataKey()
+private object IsHeader: FirDeclarationDataKey()
 
 var FirProperty.isFromVararg: Boolean? by FirDeclarationDataRegistry.data(IsFromVarargKey)
 var FirProperty.isReferredViaField: Boolean? by FirDeclarationDataRegistry.data(IsReferredViaField)
@@ -52,6 +53,7 @@ var FirDeclaration.compilerPluginMetadata: Map<String, ByteArray>? by FirDeclara
 var FirDeclaration.originalReplSnippetSymbol: FirReplSnippetSymbol? by FirDeclarationDataRegistry.data(OriginalReplSnippet)
 var FirAnonymousFunction.lambdaArgumentParent: FirQualifiedAccessExpression? by FirDeclarationDataRegistry.data(LambdaArgumentHoldsInTruths)
 var FirCallableDeclaration.fileNameForPluginGeneratedCallable: String? by FirDeclarationDataRegistry.data(FileNameForPluginGeneratedCallable)
+var FirDeclaration.isHeader: Boolean? by FirDeclarationDataRegistry.data(IsHeader)
 
 var FirDeclaration.isScriptTopLevelDeclaration: Boolean? by FirDeclarationDataRegistry.data(ScriptTopLevelDeclaration)