decaffeinate-parser/dist/mappers/mapPossiblyEmptyBlock.mjs

A better AST for CoffeeScript, inspired by CoffeeScriptRedux.

import isCommentOnlyNode from '../util/isCommentOnlyNode';
import mapBlock from './mapBlock';
/**
 * Convert a CoffeeScript block node to a decaffeinate-parser Block node,
 * carefully handling the empty block case.
 *
 * Ideally, there wouldn't need to be any special cases here, but there are a
 * few things that add complexity for now.
 * - Both decaffeinate-parser and decaffeinate expect every AST node to contain
 *   at least one token. That means that a whitespace-only empty block will
 *   cause a crash.
 * - The CoffeeScript compiler seems to sometimes give incorrect location
 *   information for empty blocks, e.g. for empty class bodies.
 * - Blocks ending in semicolons need to sometimes have that semicolon removed
 *   (e.g. when the block is treated as an expression), so an empty block that
 *   is just a semicolon should become an actual empty block and not null.
 *
 * We convert a CoffeeScript empty block to a decaffeinate-parser empty block if
 * the block is only a semicolon or if the block only consists of comments. All
 * other empty blocks result in null.
 */
export default function mapPossiblyEmptyBlock(context, node) {
    if (!node) {
        return null;
    }
    if (node.expressions.every(function (expression) { return isCommentOnlyNode(expression); })) {
        return null;
    }
    var lastSourceIndex = context.linesAndColumns.indexForLocation({
        line: node.locationData.last_line,
        column: node.locationData.last_column
    });
    if (lastSourceIndex === null) {
        throw new Error('Expected to find last source index of block.');
    }
    if (context.source[lastSourceIndex] === ';') {
        return mapBlock(context, node);
    }
    if (node.expressions.length === 0) {
        return null;
    }
    return mapBlock(context, node);
}