Function getIteratedTypeOrElementType

test/fixtures/snapshot/typescript.js:82962–83067

* When consuming an iterable type in a for..of, spread, or iterator destructuring assignment * we want to get the iterated type of an iterable for ES2015 or later, or the iterated type * of a iterable (if defined globally) or element type of an array like for ES2015 or earlier.

(use, inputType, sentType, errorNode, checkAssignability)

         * of a iterable (if defined globally) or element type of an array like for ES2015 or earlier.
         */
        function getIteratedTypeOrElementType(use, inputType, sentType, errorNode, checkAssignability) {
            var allowAsyncIterables = (use & 2 /* IterationUse.AllowsAsyncIterablesFlag */) !== 0;
            if (inputType === neverType) {
                reportTypeNotIterableError(errorNode, inputType, allowAsyncIterables); // TODO: GH#18217
                return undefined;
            }
            var uplevelIteration = languageVersion >= 2 /* ScriptTarget.ES2015 */;
            var downlevelIteration = !uplevelIteration && compilerOptions.downlevelIteration;
            var possibleOutOfBounds = compilerOptions.noUncheckedIndexedAccess && !!(use & 128 /* IterationUse.PossiblyOutOfBounds */);
            // Get the iterated type of an `Iterable<T>` or `IterableIterator<T>` only in ES2015
            // or higher, when inside of an async generator or for-await-if, or when
            // downlevelIteration is requested.
            if (uplevelIteration || downlevelIteration || allowAsyncIterables) {
                // We only report errors for an invalid iterable type in ES2015 or higher.
                var iterationTypes = getIterationTypesOfIterable(inputType, use, uplevelIteration ? errorNode : undefined);
                if (checkAssignability) {
                    if (iterationTypes) {
                        var diagnostic = use & 8 /* IterationUse.ForOfFlag */ ? ts.Diagnostics.Cannot_iterate_value_because_the_next_method_of_its_iterator_expects_type_1_but_for_of_will_always_send_0 :
                            use & 32 /* IterationUse.SpreadFlag */ ? ts.Diagnostics.Cannot_iterate_value_because_the_next_method_of_its_iterator_expects_type_1_but_array_spread_will_always_send_0 :
                                use & 64 /* IterationUse.DestructuringFlag */ ? ts.Diagnostics.Cannot_iterate_value_because_the_next_method_of_its_iterator_expects_type_1_but_array_destructuring_will_always_send_0 :
                                    use & 16 /* IterationUse.YieldStarFlag */ ? ts.Diagnostics.Cannot_delegate_iteration_to_value_because_the_next_method_of_its_iterator_expects_type_1_but_the_containing_generator_will_always_send_0 :
                                        undefined;
                        if (diagnostic) {
                            checkTypeAssignableTo(sentType, iterationTypes.nextType, errorNode, diagnostic);
                        }
                    }
                }
                if (iterationTypes || uplevelIteration) {
                    return possibleOutOfBounds ? includeUndefinedInIndexSignature(iterationTypes && iterationTypes.yieldType) : (iterationTypes && iterationTypes.yieldType);
                }
            }
            var arrayType = inputType;
            var reportedError = false;
            var hasStringConstituent = false;
            // If strings are permitted, remove any string-like constituents from the array type.
            // This allows us to find other non-string element types from an array unioned with
            // a string.
            if (use & 4 /* IterationUse.AllowsStringInputFlag */) {
                if (arrayType.flags & 1048576 /* TypeFlags.Union */) {
                    // After we remove all types that are StringLike, we will know if there was a string constituent
                    // based on whether the result of filter is a new array.
                    var arrayTypes = inputType.types;
                    var filteredTypes = ts.filter(arrayTypes, function (t) { return !(t.flags & 402653316 /* TypeFlags.StringLike */); });
                    if (filteredTypes !== arrayTypes) {
                        arrayType = getUnionType(filteredTypes, 2 /* UnionReduction.Subtype */);
                    }
                }
                else if (arrayType.flags & 402653316 /* TypeFlags.StringLike */) {
                    arrayType = neverType;
                }
                hasStringConstituent = arrayType !== inputType;
                if (hasStringConstituent) {
                    if (languageVersion < 1 /* ScriptTarget.ES5 */) {
                        if (errorNode) {
                            error(errorNode, ts.Diagnostics.Using_a_string_in_a_for_of_statement_is_only_supported_in_ECMAScript_5_and_higher);
                            reportedError = true;
                        }
                    }