src/Fixer/ReturnNotation/SimplifiedNullReturnFixer.php
private function isStrictOrNullableReturnTypeFunction(Tokens $tokens, $returnIndex)
    {
        $functionIndex = $returnIndex;
        do {
            $functionIndex = $tokens->getPrevTokenOfKind($functionIndex, [[T_FUNCTION]]);
            if (null === $functionIndex) {
                return false;
            }
            $openingCurlyBraceIndex = $tokens->getNextTokenOfKind($functionIndex, ['{']);
            $closingCurlyBraceIndex = $tokens->findBlockEnd(Tokens::BLOCK_TYPE_CURLY_BRACE, $openingCurlyBraceIndex);
        } while ($closingCurlyBraceIndex < $returnIndex);

        $possibleVoidIndex = $tokens->getPrevMeaningfulToken($openingCurlyBraceIndex);
        $isStrictReturnType = $tokens[$possibleVoidIndex]->isGivenKind(T_STRING) && 'void' !== $tokens[$possibleVoidIndex]->getContent();

        $nullableTypeIndex = $tokens->getNextTokenOfKind($functionIndex, [[CT::T_NULLABLE_TYPE]]);
        $isNullableReturnType = null !== $nullableTypeIndex && $nullableTypeIndex < $openingCurlyBraceIndex;

        return $isStrictReturnType || $isNullableReturnType;
    }
private function isStrictOrNullableReturnTypeFunction(Tokens $tokens, $returnIndex)
    {
        $functionIndex = $returnIndex;
        do {
            $functionIndex = $tokens->getPrevTokenOfKind($functionIndex, [[T_FUNCTION]]);
            if (null === $functionIndex) {
                return false;
            }
            $openingCurlyBraceIndex = $tokens->getNextTokenOfKind($functionIndex, ['{']);
            $closingCurlyBraceIndex = $tokens->findBlockEnd(Tokens::BLOCK_TYPE_CURLY_BRACE, $openingCurlyBraceIndex);
        } while ($closingCurlyBraceIndex < $returnIndex);

        $possibleVoidIndex = $tokens->getPrevMeaningfulToken($openingCurlyBraceIndex);
        $isStrictReturnType = $tokens[$possibleVoidIndex]->isGivenKind(T_STRING) && 'void' !== $tokens[$possibleVoidIndex]->getContent();

        $nullableTypeIndex = $tokens->getNextTokenOfKind($functionIndex, [[CT::T_NULLABLE_TYPE]]);
        $isNullableReturnType = null !== $nullableTypeIndex && $nullableTypeIndex < $openingCurlyBraceIndex;

        return $isStrictReturnType || $isNullableReturnType;
    }
Is the return within a function with a non-void or nullable return type?

@param Tokens $tokens
@param int    $returnIndex Current return token index

@return bool