/*
 * Copyright 2010-2020 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.extra

import org.jetbrains.kotlin.KtFakeSourceElementKind
import org.jetbrains.kotlin.fir.analysis.checkers.context.CheckerContext
import org.jetbrains.kotlin.fir.analysis.checkers.declaration.FirSimpleFunctionChecker
import org.jetbrains.kotlin.diagnostics.DiagnosticReporter
import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors
import org.jetbrains.kotlin.diagnostics.reportOn
import org.jetbrains.kotlin.fir.analysis.checkers.MppCheckerKind
import org.jetbrains.kotlin.fir.declarations.FirSimpleFunction
import org.jetbrains.kotlin.fir.expressions.impl.FirSingleExpressionBlock
import org.jetbrains.kotlin.fir.resolve.fullyExpandedType
import org.jetbrains.kotlin.fir.types.coneType
import org.jetbrains.kotlin.fir.types.isUnit

object RedundantReturnUnitType : FirSimpleFunctionChecker(MppCheckerKind.Common) {
    context(context: CheckerContext, reporter: DiagnosticReporter)
    override fun check(declaration: FirSimpleFunction) {
        if (declaration.body is FirSingleExpressionBlock) return
        val returnType = declaration.returnTypeRef
        if (returnType.source == null) return
        if (declaration.source?.kind is KtFakeSourceElementKind) return
        if (returnType.annotations.isNotEmpty()) return

        if (returnType.coneType.fullyExpandedType().isUnit) {
            reporter.reportOn(declaration.returnTypeRef.source, FirErrors.REDUNDANT_RETURN_UNIT_TYPE)
        }
    }

}
