FIR checker: add diagnostic EXPECTED_DECLARATION_WITH_BODY

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirDeclarationCheckerUtils.kt

@@ -5,10 +5,24 @@
 
 package org.jetbrains.kotlin.fir.analysis.checkers.declaration
 
+import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.checkers.extended.report
+import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.FirRegularClass
+import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
+import org.jetbrains.kotlin.fir.declarations.hasBody
 import org.jetbrains.kotlin.fir.declarations.isExpect
 
 // Note that the class that contains the currently visiting declaration will *not* be in the context's containing declarations *yet*.
 internal fun isInsideExpectClass(containingDeclaration: FirRegularClass, context: CheckerContext): Boolean =
     containingDeclaration.isExpect || context.containingDeclarations.asReversed().any { it is FirRegularClass && it.isExpect }
+
+internal fun checkExpectFunction(function: FirSimpleFunction, reporter: DiagnosticReporter) {
+    val source = function.source ?: return
+    if (source.kind is FirFakeSourceElementKind) return
+    if (function.hasBody) {
+        reporter.report(source, FirErrors.EXPECTED_DECLARATION_WITH_BODY)
+    }
+}

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirMemberFunctionChecker.kt

@@ -60,6 +60,11 @@ object FirMemberFunctionChecker : FirRegularClassChecker() {
                 reporter.report(FirErrors.NON_ABSTRACT_FUNCTION_WITH_NO_BODY.on(source, function))
             }
         }
+
+        val isExpect = function.isExpect || modifierList?.modifiers?.any { it.token == KtTokens.EXPECT_KEYWORD } == true
+        if (isExpect) {
+            checkExpectFunction(function, reporter)
+        }
     }
 
 }

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/declaration/FirTopLevelFunctionChecker.kt

@@ -7,7 +7,6 @@ package org.jetbrains.kotlin.fir.analysis.checkers.declaration
 
 import org.jetbrains.kotlin.fir.FirFakeSourceElementKind
 import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
-import org.jetbrains.kotlin.fir.analysis.checkers.extended.report
 import org.jetbrains.kotlin.fir.analysis.diagnostics.DiagnosticReporter
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
 import org.jetbrains.kotlin.fir.declarations.*
@@ -35,5 +34,9 @@ object FirTopLevelFunctionChecker : FirFileChecker() {
         if (!function.hasBody && !hasAbstractModifier && !isExternal && !isExpect) {
             reporter.report(FirErrors.NON_MEMBER_FUNCTION_NO_BODY.on(source, function))
         }
+
+        if (isExpect) {
+            checkExpectFunction(function, reporter)
+        }
     }
 }

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirDefaultErrorMessages.kt

@@ -50,6 +50,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DESERIALIZATION_E
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EMPTY_RANGE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.ENUM_AS_SUPERTYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.ERROR_FROM_JAVA_RESOLUTION
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPECTED_DECLARATION_WITH_BODY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPLICIT_DELEGATION_CALL_REQUIRED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPOSED_FUNCTION_RETURN_TYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EXPOSED_PARAMETER_TYPE
@@ -394,6 +395,9 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(PRIVATE_SETTER_FOR_ABSTRACT_PROPERTY, "Private setters are not allowed for abstract properties")
             map.put(PRIVATE_SETTER_FOR_OPEN_PROPERTY, "Private setters are not allowed for open properties")
 
+            // Multi-platform projects
+            map.put(EXPECTED_DECLARATION_WITH_BODY, "Expected declaration must not have a body")
+
             // Destructuring declaration
             map.put(INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION, "Initializer required for destructuring declaration")
             map.put(

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -180,6 +180,9 @@ object FirErrors {
     val PRIVATE_SETTER_FOR_ABSTRACT_PROPERTY by error0<FirSourceElement, PsiElement>()
     val PRIVATE_SETTER_FOR_OPEN_PROPERTY by error0<FirSourceElement, PsiElement>()
 
+    // Multi-platform projects
+    val EXPECTED_DECLARATION_WITH_BODY by error0<FirSourceElement, KtDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
+
     // Destructuring declaration
     val INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION by error0<FirSourceElement, KtDestructuringDeclaration>()
     val COMPONENT_FUNCTION_MISSING by error2<FirSourceElement, PsiElement, Name, FirTypeRef>()

compiler/testData/diagnostics/tests/modifiers/openInExpectInterface.fir.kt

@@ -5,7 +5,7 @@
 
 expect interface My {
     open fun bar()
-    open fun bas() {}
+    <!EXPECTED_DECLARATION_WITH_BODY!>open fun bas()<!> {}
     <!REDUNDANT_MODIFIER!>open<!> abstract fun bat(): Int
 
     fun foo()

compiler/testData/diagnostics/tests/multiplatform/headerClass/headerClassWithFunctionBody.fir.kt

@@ -21,7 +21,7 @@ expect class Foo(
         get() = "no"
         set(value) {}
 
-    fun functionWithBody(x: Int): Int {
+    <!EXPECTED_DECLARATION_WITH_BODY!>fun functionWithBody(x: Int): Int<!> {
         return x + 1
     }
 }

compiler/testData/diagnostics/tests/multiplatform/topLevelFun/headerDeclarationWithBody.fir.kt

@@ -1,9 +0,0 @@
-// !LANGUAGE: +MultiPlatformProjects
-// MODULE: m1-common
-// FILE: common.kt
-
-<!CONFLICTING_OVERLOADS!>expect fun foo()<!>
-
-<!CONFLICTING_OVERLOADS!>expect fun foo()<!> {}
-
-expect fun bar() {}

compiler/testData/diagnostics/tests/multiplatform/topLevelFun/headerDeclarationWithBody.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !LANGUAGE: +MultiPlatformProjects
 // MODULE: m1-common
 // FILE: common.kt