Function transformAndSpreadElements

test/fixtures/snapshot/typescript.js:101293–101356

* Transforms an array of Expression nodes that contains a SpreadExpression. * * @param elements The array of Expression nodes. * @param isArgumentList A value indicating whether to ensure that the result is a fresh array. * This should be `false` when spreading in

(elements, isArgumentList, multiLine, hasTrailingComma)

         * @param multiLine A value indicating whether the result should be emitted on multiple lines.
         */
        function transformAndSpreadElements(elements, isArgumentList, multiLine, hasTrailingComma) {
            // When there is no leading SpreadElement:
            //
            // [source]
            //      [a, ...b, c]
            //
            // [output (downlevelIteration)]
            //      __spreadArray(__spreadArray([a], __read(b)), [c])
            //
            // [output]
            //      __spreadArray(__spreadArray([a], b), [c])
            //
            // When there *is* a leading SpreadElement:
            //
            // [source]
            //      [...a, b]
            //
            // [output (downlevelIteration)]
            //      __spreadArray(__spreadArray([], __read(a)), [b])
            //
            // [output]
            //      __spreadArray(__spreadArray([], a), [b])
            //
            // NOTE: We use `isPackedArrayLiteral` below rather than just `isArrayLiteral`
            // because ES2015 spread will replace _missing_ array elements with `undefined`,
            // so we cannot just use an array as is. For example:
            //
            // `[1, ...[2, , 3]]` becomes `[1, 2, undefined, 3]`
            //
            // However, for packed array literals (i.e., an array literal with no OmittedExpression
            // elements), we can use the array as-is.
            // Map spans of spread expressions into their expressions and spans of other
            // expressions into an array literal.
            var numElements = elements.length;
            var segments = ts.flatten(
            // As we visit each element, we return one of two functions to use as the "key":
            // - `visitSpanOfSpreads` for one or more contiguous `...` spread expressions, i.e. `...a, ...b` in `[1, 2, ...a, ...b]`
            // - `visitSpanOfNonSpreads` for one or more contiguous non-spread elements, i.e. `1, 2`, in `[1, 2, ...a, ...b]`
            ts.spanMap(elements, partitionSpread, function (partition, visitPartition, _start, end) {
                return visitPartition(partition, multiLine, hasTrailingComma && end === numElements);
            }));
            if (segments.length === 1) {
                var firstSegment = segments[0];
                // If we don't need a unique copy, then we are spreading into an argument list for
                // a CallExpression or NewExpression. When using `--downlevelIteration`, we need
                // to coerce this into an array for use with `apply`, so we will use the code path
                // that follows instead.
                if (isArgumentList && !compilerOptions.downlevelIteration
                    || ts.isPackedArrayLiteral(firstSegment.expression) // see NOTE (above)
                    || ts.isCallToHelper(firstSegment.expression, "___spreadArray")) {
                    return firstSegment.expression;
                }
            }
            var helpers = emitHelpers();
            var startsWithSpread = segments[0].kind !== 0 /* SpreadSegmentKind.None */;
            var expression = startsWithSpread ? factory.createArrayLiteralExpression() :
                segments[0].expression;
            for (var i = startsWithSpread ? 0 : 1; i < segments.length; i++) {