FIR checker: introduce top-level function checker

compiler/fir/analysis-tests/testData/resolve/arguments/operatorsOverLiterals.fir.txt

@@ -19,7 +19,8 @@ FILE: operatorsOverLiterals.kt
     }
     public final fun R|kotlin/Int|.bar(): R|kotlin/Int| {
     }
-    public final fun R|kotlin/Int|.baz(): R|kotlin/Int|
+    public final fun R|kotlin/Int|.baz(): R|kotlin/Int| {
+    }
     public final fun R|kotlin/Byte|.baz(): R|kotlin/Byte| {
     }
     public final fun test_3(): R|kotlin/Unit| {

compiler/fir/analysis-tests/testData/resolve/arguments/operatorsOverLiterals.kt

@@ -20,7 +20,7 @@ fun test_2(n: Int) {
 
 fun Int.bar(): Int {}
 
-fun Int.baz(): Int
+fun Int.baz(): Int {}
 fun Byte.baz(): Byte {}
 
 fun test_3() {

compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingOverloads.fir.txt

@@ -111,7 +111,8 @@ FILE: conflictingOverloads.kt
         }
 
     }
-    public final fun mest(): R|kotlin/Unit|
+    public final fun mest(): R|kotlin/Unit| {
+    }
     public final class mest : R|kotlin/Any| {
         public constructor(): R|mest| {
             super<R|kotlin/Any|>()

compiler/fir/analysis-tests/testData/resolve/diagnostics/conflictingOverloads.kt

@@ -59,7 +59,7 @@ class L {
     fun B.foo() {}
 }
 
-fun mest()
+fun mest() {}
 
 class mest
 

compiler/fir/analysis-tests/testData/resolve/intersectionTypes.kt

@@ -5,7 +5,7 @@ interface B
 class Clazz1 : A, B
 class Clazz2 : A, B
 
-fun <K> select(x: K, y: K): K
+<!NON_MEMBER_FUNCTION_NO_BODY!>fun <K> select(x: K, y: K): K<!>
 
 fun test() = select(Clazz1(), Clazz2())
 

compiler/fir/analysis-tests/testData/resolve/multifile/simpleStarImport.kt

@@ -14,7 +14,7 @@ package a.d
 
 import b.d.*
 
-fun foo(arg: Other): Another
+<!NON_MEMBER_FUNCTION_NO_BODY!>fun foo(arg: Other): Another<!>
 
 fun bar() {
     baz()

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

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2010-2021 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.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.*
+import org.jetbrains.kotlin.lexer.KtTokens
+
+// See old FE's [DeclarationsChecker]
+object FirTopLevelFunctionChecker : FirFileChecker() {
+    override fun check(declaration: FirFile, context: CheckerContext, reporter: DiagnosticReporter) {
+        for (topLevelDeclaration in declaration.declarations) {
+            if (topLevelDeclaration is FirSimpleFunction) {
+                checkFunction(topLevelDeclaration, reporter)
+            }
+        }
+    }
+
+    private fun checkFunction(function: FirSimpleFunction, reporter: DiagnosticReporter) {
+        val source = function.source ?: return
+        if (source.kind is FirFakeSourceElementKind) return
+        // If multiple (potentially conflicting) modality modifiers are specified, not all modifiers are recorded at `status`.
+        // So, our source of truth should be the full modifier list retrieved from the source.
+        val modifierList = with(FirModifierList) { source.getModifierList() }
+        val hasAbstractModifier = modifierList?.modifiers?.any { it.token == KtTokens.ABSTRACT_KEYWORD } == true
+        val isExternal = function.isExternal || modifierList?.modifiers?.any { it.token == KtTokens.EXTERNAL_KEYWORD } == true
+        val isExpect = function.isExpect || modifierList?.modifiers?.any { it.token == KtTokens.EXPECT_KEYWORD } == true
+        if (!function.hasBody && !hasAbstractModifier && !isExternal && !isExpect) {
+            reporter.report(FirErrors.NON_MEMBER_FUNCTION_NO_BODY.on(source, function))
+        }
+    }
+}

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

@@ -80,6 +80,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MANY_COMPANION_OB
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.MISSING_VAL_ON_ANNOTATION_PARAMETER
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NONE_APPLICABLE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_ABSTRACT_FUNCTION_WITH_NO_BODY
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_MEMBER_FUNCTION_NO_BODY
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_ENUM
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NON_PRIVATE_CONSTRUCTOR_IN_SEALED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.NOT_AN_ANNOTATION_CLASS
@@ -359,6 +360,7 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
             map.put(ABSTRACT_FUNCTION_WITH_BODY, "A function ''{0}'' with body cannot be abstract", DECLARATION_NAME)
             map.put(NON_ABSTRACT_FUNCTION_WITH_NO_BODY, "Function ''{0}'' without a body must be abstract", DECLARATION_NAME)
             map.put(PRIVATE_FUNCTION_WITH_NO_BODY, "Function ''{0}'' without body cannot be private", DECLARATION_NAME)
+            map.put(NON_MEMBER_FUNCTION_NO_BODY, "Function ''{0}'' must have a body", DECLARATION_NAME)
 
             map.put(FUNCTION_DECLARATION_WITH_NO_NAME, "Function declaration must have a name")
 

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

@@ -155,6 +155,7 @@ object FirErrors {
     val ABSTRACT_FUNCTION_WITH_BODY by error1<FirSourceElement, KtFunction, FirMemberDeclaration>(SourceElementPositioningStrategies.MODALITY_MODIFIER)
     val NON_ABSTRACT_FUNCTION_WITH_NO_BODY by error1<FirSourceElement, KtFunction, FirMemberDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
     val PRIVATE_FUNCTION_WITH_NO_BODY by error1<FirSourceElement, KtFunction, FirMemberDeclaration>(SourceElementPositioningStrategies.VISIBILITY_MODIFIER)
+    val NON_MEMBER_FUNCTION_NO_BODY by error1<FirSourceElement, KtFunction, FirMemberDeclaration>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
 
     val FUNCTION_DECLARATION_WITH_NO_NAME by error0<FirSourceElement, KtFunction>(SourceElementPositioningStrategies.DECLARATION_SIGNATURE)
 

compiler/fir/entrypoint/src/org/jetbrains/kotlin/fir/checkers/CommonDeclarationCheckers.kt

@@ -59,6 +59,10 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
         FirConstructorAllowedChecker,
     )
 
+    override val fileCheckers: Set<FirFileChecker> = setOf(
+        FirTopLevelFunctionChecker,
+    )
+
     override val controlFlowAnalyserCheckers: Set<FirControlFlowChecker> = setOf(
         FirCallsEffectAnalyzer,
         FirReturnsImpliesAnalyzer,

compiler/testData/diagnostics/tests/Abstract.fir.kt

@@ -22,7 +22,7 @@ package MyPackage
     abstract val e3: Int = 0; get() = a
 
     //methods
-    fun f()
+    <!NON_MEMBER_FUNCTION_NO_BODY!>fun f()<!>
     fun g() {}
     abstract fun h()
     abstract fun j() {}

compiler/testData/diagnostics/tests/DefaultValuesCheckWithoutBody.fir.kt

@@ -6,4 +6,4 @@ abstract class Abst {
     abstract fun foo(x: Int = <!UNRESOLVED_REFERENCE!>y<!>, y: Int = x)
 }
 
-fun extraDiagnostics(x: Int = <!UNRESOLVED_REFERENCE!>y<!>, y: Int)
+<!NON_MEMBER_FUNCTION_NO_BODY!>fun extraDiagnostics(x: Int = <!UNRESOLVED_REFERENCE!>y<!>, y: Int)<!>

compiler/testData/diagnostics/tests/incompleteCode/diagnosticWithSyntaxError/namedFun.fir.kt

@@ -1 +0,0 @@
-fun bar()

compiler/testData/diagnostics/tests/incompleteCode/diagnosticWithSyntaxError/namedFun.kt

@@ -1 +1,2 @@
+// FIR_IDENTICAL
 <!NON_MEMBER_FUNCTION_NO_BODY!>fun bar()<!>

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

@@ -7,6 +7,6 @@ expect fun foo()
 // MODULE: m2-jvm(m1-common)
 // FILE: jvm.kt
 
-actual fun foo()
+<!NON_MEMBER_FUNCTION_NO_BODY!>actual fun foo()<!>
 
-actual fun bar()
+<!NON_MEMBER_FUNCTION_NO_BODY!>actual fun bar()<!>