Function elaborateArrowFunction

test/fixtures/snapshot/typescript.js:63945–63987

(node, source, target, relation, containingMessageChain, errorOutputContainer)

            return false;
        }
        function elaborateArrowFunction(node, source, target, relation, containingMessageChain, errorOutputContainer) {
            // Don't elaborate blocks
            if (ts.isBlock(node.body)) {
                return false;
            }
            // Or functions with annotated parameter types
            if (ts.some(node.parameters, ts.hasType)) {
                return false;
            }
            var sourceSig = getSingleCallSignature(source);
            if (!sourceSig) {
                return false;
            }
            var targetSignatures = getSignaturesOfType(target, 0 /* SignatureKind.Call */);
            if (!ts.length(targetSignatures)) {
                return false;
            }
            var returnExpression = node.body;
            var sourceReturn = getReturnTypeOfSignature(sourceSig);
            var targetReturn = getUnionType(ts.map(targetSignatures, getReturnTypeOfSignature));
            if (!checkTypeRelatedTo(sourceReturn, targetReturn, relation, /*errorNode*/ undefined)) {
                var elaborated = returnExpression && elaborateError(returnExpression, sourceReturn, targetReturn, relation, /*headMessage*/ undefined, containingMessageChain, errorOutputContainer);
                if (elaborated) {
                    return elaborated;
                }
                var resultObj = errorOutputContainer || {};
                checkTypeRelatedTo(sourceReturn, targetReturn, relation, returnExpression, /*message*/ undefined, containingMessageChain, resultObj);
                if (resultObj.errors) {
                    if (target.symbol && ts.length(target.symbol.declarations)) {
                        ts.addRelatedInfo(resultObj.errors[resultObj.errors.length - 1], ts.createDiagnosticForNode(target.symbol.declarations[0], ts.Diagnostics.The_expected_type_comes_from_the_return_type_of_this_signature));
                    }
                    if ((ts.getFunctionFlags(node) & 2 /* FunctionFlags.Async */) === 0
                        // exclude cases where source itself is promisy - this way we don't make a suggestion when relating
                        // an IPromise and a Promise that are slightly different
                        && !getTypeOfPropertyOfType(sourceReturn, "then")
                        && checkTypeRelatedTo(createPromiseType(sourceReturn), targetReturn, relation, /*errorNode*/ undefined)) {
                        ts.addRelatedInfo(resultObj.errors[resultObj.errors.length - 1], ts.createDiagnosticForNode(node, ts.Diagnostics.Did_you_mean_to_mark_this_function_as_async));
                    }
                    return true;
                }
            }
            return false;
        }
        function getBestMatchIndexedAccessTypeOrUndefined(source, target, nameType) {
            var idx = getIndexedAccessTypeOrUndefined(target, nameType);
            if (idx) {