[FIR] Add DEPRECATED_TYPE_PARAMETER_SYNTAX check

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -332,6 +332,8 @@ object DIAGNOSTICS_LIST : DiagnosticList() {
         }
 
         val CYCLIC_GENERIC_UPPER_BOUND by error<FirSourceElement, PsiElement>()
+
+        val DEPRECATED_TYPE_PARAMETER_SYNTAX by error<FirSourceElement, KtTypeParameterList>()
     }
 
     val REFLECTION by object : DiagnosticGroup("Reflection") {

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

@@ -241,6 +241,7 @@ object FirErrors {
     val TYPE_PARAMETER_OF_PROPERTY_NOT_USED_IN_RECEIVER by error0<FirSourceElement, KtTypeParameter>()
     val RETURN_TYPE_MISMATCH by error2<FirSourceElement, KtExpression, ConeKotlinType, ConeKotlinType>(SourceElementPositioningStrategies.WHOLE_ELEMENT)
     val CYCLIC_GENERIC_UPPER_BOUND by error0<FirSourceElement, PsiElement>()
+    val DEPRECATED_TYPE_PARAMETER_SYNTAX by error0<FirSourceElement, KtTypeParameterList>()
 
     // Reflection
     val EXTENSION_IN_CLASS_REFERENCE_NOT_ALLOWED by error1<FirSourceElement, KtExpression, FirCallableDeclaration<*>>(SourceElementPositioningStrategies.REFERENCE_BY_QUALIFIED)

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

@@ -44,6 +44,7 @@ object FirCyclicTypeBoundsChecker : FirMemberDeclarationChecker() {
             declaration.typeParameters
                 .filter { cycles.contains(it.symbol.name) }
                 .forEach { param ->
+                    //for some reason FE 1.0 report differently for class declarations
                     val targets = if (declaration is FirRegularClass) {
                         param.symbol.fir.originalBounds().filter { cycles.contains(extractTypeParamName(it.coneType)) }
                             .mapNotNull { it.source }

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

@@ -0,0 +1,31 @@
+/*
+ * 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.FirFakeSourceElement
+import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
+import org.jetbrains.kotlin.fir.analysis.diagnostics.*
+import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
+import org.jetbrains.kotlin.fir.toFirLightSourceElement
+
+object FirFunctionTypeParametersChecker : FirSimpleFunctionChecker() {
+
+    override fun check(declaration: FirSimpleFunction, context: CheckerContext, reporter: DiagnosticReporter) {
+        declaration.source?.let { source ->
+            if (source is FirFakeSourceElement<*>) return
+
+            val typeParamsNode = source.treeStructure.typeParametersList(source.lighterASTNode)
+            val nameNode = source.treeStructure.nameIdentifier(source.lighterASTNode)
+            if (typeParamsNode != null && nameNode != null && typeParamsNode.startOffset > nameNode.startOffset) {
+                reporter.reportOn(
+                    typeParamsNode.toFirLightSourceElement(source.treeStructure),
+                    FirErrors.DEPRECATED_TYPE_PARAMETER_SYNTAX,
+                    context
+                )
+            }
+        }
+    }
+}

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

@@ -79,6 +79,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DELEGATED_PROPERT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DELEGATION_IN_INTERFACE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DELEGATION_SUPER_CALL_IN_ENUM_CONSTRUCTOR
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DEPRECATED_MODIFIER_PAIR
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DEPRECATED_TYPE_PARAMETER_SYNTAX
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.DESERIALIZATION_ERROR
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.EMPTY_RANGE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.ENUM_AS_SUPERTYPE
@@ -512,6 +513,8 @@ class FirDefaultErrorMessages : DefaultErrorMessages.Extension {
 
             map.put(CYCLIC_GENERIC_UPPER_BOUND, "Type parameter has cyclic upper bounds")
 
+            map.put(DEPRECATED_TYPE_PARAMETER_SYNTAX, "Type parameters must be placed before the name of the function")
+
             // Reflection
             map.put(
                 EXTENSION_IN_CLASS_REFERENCE_NOT_ALLOWED,

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

@@ -577,7 +577,7 @@ private fun FlyweightCapableTreeStructure<LighterASTNode>.ifKeyword(node: Lighte
 private fun FlyweightCapableTreeStructure<LighterASTNode>.returnKeyword(node: LighterASTNode): LighterASTNode? =
     findChildByType(node, KtTokens.RETURN_KEYWORD)
 
-private fun FlyweightCapableTreeStructure<LighterASTNode>.nameIdentifier(node: LighterASTNode): LighterASTNode? =
+internal fun FlyweightCapableTreeStructure<LighterASTNode>.nameIdentifier(node: LighterASTNode): LighterASTNode? =
     findChildByType(node, KtTokens.IDENTIFIER)
 
 private fun FlyweightCapableTreeStructure<LighterASTNode>.operationReference(node: LighterASTNode): LighterASTNode? =

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

@@ -35,7 +35,8 @@ object CommonDeclarationCheckers : DeclarationCheckers() {
     )
 
     override val simpleFunctionCheckers: Set<FirSimpleFunctionChecker> = setOf(
-        FirFunctionNameChecker
+        FirFunctionNameChecker,
+        FirFunctionTypeParametersChecker,
     )
 
     override val propertyCheckers: Set<FirPropertyChecker> = setOf(

compiler/testData/diagnostics/tests/typeParameters/deprecatedSyntax.fir.kt

@@ -1,3 +0,0 @@
-fun foo<T>() {
-    fun bar<T>() {}
-}

compiler/testData/diagnostics/tests/typeParameters/deprecatedSyntax.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 fun foo<!DEPRECATED_TYPE_PARAMETER_SYNTAX!><T><!>() {
     fun bar<!DEPRECATED_TYPE_PARAMETER_SYNTAX!><T><!>() {}
 }

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDataClassConverters.kt

@@ -1024,6 +1024,12 @@ internal val KT_DIAGNOSTIC_CONVERTER = KtDiagnosticConverterBuilder.buildConvert
             token,
         )
     }
+    add(FirErrors.DEPRECATED_TYPE_PARAMETER_SYNTAX) { firDiagnostic ->
+        DeprecatedTypeParameterSyntaxImpl(
+            firDiagnostic as FirPsiDiagnostic<*>,
+            token,
+        )
+    }
     add(FirErrors.EXTENSION_IN_CLASS_REFERENCE_NOT_ALLOWED) { firDiagnostic ->
         ExtensionInClassReferenceNotAllowedImpl(
             firSymbolBuilder.callableBuilder.buildCallableSymbol(firDiagnostic.a as FirCallableDeclaration),

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnostics.kt

@@ -723,10 +723,14 @@ sealed class KtFirDiagnostic<PSI: PsiElement> : KtDiagnosticWithPsi<PSI> {
         abstract val actual: KtType
     }
 
-    abstract class CyclicGenericUpperBound : KtFirDiagnostic<KtTypeParameter>() {
+    abstract class CyclicGenericUpperBound : KtFirDiagnostic<PsiElement>() {
         override val diagnosticClass get() = CyclicGenericUpperBound::class
     }
 
+    abstract class DeprecatedTypeParameterSyntax : KtFirDiagnostic<KtTypeParameterList>() {
+        override val diagnosticClass get() = DeprecatedTypeParameterSyntax::class
+    }
+
     abstract class ExtensionInClassReferenceNotAllowed : KtFirDiagnostic<KtExpression>() {
         override val diagnosticClass get() = ExtensionInClassReferenceNotAllowed::class
         abstract val referencedDeclaration: KtCallableSymbol

idea/idea-frontend-fir/src/org/jetbrains/kotlin/idea/frontend/api/fir/diagnostics/KtFirDiagnosticsImpl.kt

@@ -1171,7 +1171,14 @@ internal class ReturnTypeMismatchImpl(
 internal class CyclicGenericUpperBoundImpl(
     firDiagnostic: FirPsiDiagnostic<*>,
     override val token: ValidityToken,
-) : KtFirDiagnostic.CyclicGenericUpperBound(), KtAbstractFirDiagnostic<KtTypeParameter> {
+) : KtFirDiagnostic.CyclicGenericUpperBound(), KtAbstractFirDiagnostic<PsiElement> {
+    override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
+}
+
+internal class DeprecatedTypeParameterSyntaxImpl(
+    firDiagnostic: FirPsiDiagnostic<*>,
+    override val token: ValidityToken,
+) : KtFirDiagnostic.DeprecatedTypeParameterSyntax(), KtAbstractFirDiagnostic<KtTypeParameterList> {
     override val firDiagnostic: FirPsiDiagnostic<*> by weakRef(firDiagnostic)
 }