babel/packages/babylon/src/parser/comments.js

/* @flow */

/**
 * Based on the comment attachment algorithm used in espree and estraverse.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * * Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * * Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

import Parser from "./index";

function last(stack) {
  return stack[stack.length - 1];
}

const pp = Parser.prototype;

pp.addComment = function (comment) {
  this.state.trailingComments.push(comment);
  this.state.leadingComments.push(comment);
};

pp.processComment = function (node) {
  if (node.type === "Program" && node.body.length > 0) return;

  let stack = this.state.commentStack;

  let lastChild, trailingComments, i;

  if (this.state.trailingComments.length > 0) {
    // If the first comment in trailingComments comes after the
    // current node, then we're good - all comments in the array will
    // come after the node and so it's safe to add them as official
    // trailingComments.
    if (this.state.trailingComments[0].start >= node.end) {
      trailingComments = this.state.trailingComments;
      this.state.trailingComments = [];
    } else {
      // Otherwise, if the first comment doesn't come after the
      // current node, that means we have a mix of leading and trailing
      // comments in the array and that leadingComments contains the
      // same items as trailingComments. Reset trailingComments to
      // zero items and we'll handle this by evaluating leadingComments
      // later.
      this.state.trailingComments.length = 0;
    }
  } else {
    let lastInStack = last(stack);
    if (stack.length > 0 && lastInStack.trailingComments && lastInStack.trailingComments[0].start >= node.end) {
      trailingComments = lastInStack.trailingComments;
      lastInStack.trailingComments = null;
    }
  }

  // Eating the stack.
  while (stack.length > 0 && last(stack).start >= node.start) {
    lastChild = stack.pop();
  }

  if (lastChild) {
    if (lastChild.leadingComments) {
      if (lastChild !== node && last(lastChild.leadingComments).end <= node.start) {
        node.leadingComments = lastChild.leadingComments;
        lastChild.leadingComments = null;
      } else {
        // A leading comment for an anonymous class had been stolen by its first ClassMethod,
        // so this takes back the leading comment.
        // See also: https://github.com/eslint/espree/issues/158
        for (i = lastChild.leadingComments.length - 2; i >= 0; --i) {
          if (lastChild.leadingComments[i].end <= node.start) {
            node.leadingComments = lastChild.leadingComments.splice(0, i + 1);
            break;
          }
        }
      }
    }
  } else if (this.state.leadingComments.length > 0) {
    if (last(this.state.leadingComments).end <= node.start) {
      node.leadingComments = this.state.leadingComments;
      this.state.leadingComments = [];
    } else {
      // https://github.com/eslint/espree/issues/2
      //
      // In special cases, such as return (without a value) and
      // debugger, all comments will end up as leadingComments and
      // will otherwise be eliminated. This step runs when the
      // commentStack is empty and there are comments left
      // in leadingComments.
      //
      // This loop figures out the stopping point between the actual
      // leading and trailing comments by finding the location of the
      // first comment that comes after the given node.
      for (i = 0; i < this.state.leadingComments.length; i++) {
        if (this.state.leadingComments[i].end > node.start) {
          break;
        }
      }

      // Split the array based on the location of the first comment
      // that comes after the node. Keep in mind that this could
      // result in an empty array, and if so, the array must be
      // deleted.
      node.leadingComments = this.state.leadingComments.slice(0, i);
      if (node.leadingComments.length === 0) {
        node.leadingComments = null;
      }

      // Similarly, trailing comments are attached later. The variable
      // must be reset to null if there are no trailing comments.
      trailingComments = this.state.leadingComments.slice(i);
      if (trailingComments.length === 0) {
        trailingComments = null;
      }
    }
  }

  if (trailingComments) {
    if (trailingComments.length && trailingComments[0].start >= node.start && last(trailingComments).end <= node.end) {
      node.innerComments = trailingComments;
    } else {
      node.trailingComments = trailingComments;
    }
  }

  stack.push(node);
};