patcher.js

var assert = require("assert");
var linesModule = require("./lines");
var types = require("./types");
var getFieldValue = types.getFieldValue;
var Printable = types.namedTypes.Printable;
var Expression = types.namedTypes.Expression;
var SourceLocation = types.namedTypes.SourceLocation;
var util = require("./util");
var comparePos = util.comparePos;
var FastPath = require("./fast-path");
var isObject = types.builtInTypes.object;
var isArray = types.builtInTypes.array;
var isString = types.builtInTypes.string;
var riskyAdjoiningCharExp = /[0-9a-z_$]/i;

function Patcher(lines) {
    assert.ok(this instanceof Patcher);
    assert.ok(lines instanceof linesModule.Lines);

    var self = this,
        replacements = [];

    self.replace = function(loc, lines) {
        if (isString.check(lines))
            lines = linesModule.fromString(lines);

        replacements.push({
            lines: lines,
            start: loc.start,
            end: loc.end
        });
    };

    self.get = function(loc) {
        // If no location is provided, return the complete Lines object.
        loc = loc || {
            start: { line: 1, column: 0 },
            end: { line: lines.length,
                   column: lines.getLineLength(lines.length) }
        };

        var sliceFrom = loc.start,
            toConcat = [];

        function pushSlice(from, to) {
            assert.ok(comparePos(from, to) <= 0);
            toConcat.push(lines.slice(from, to));
        }

        replacements.sort(function(a, b) {
            return comparePos(a.start, b.start);
        }).forEach(function(rep) {
            if (comparePos(sliceFrom, rep.start) > 0) {
                // Ignore nested replacement ranges.
            } else {
                pushSlice(sliceFrom, rep.start);
                toConcat.push(rep.lines);
                sliceFrom = rep.end;
            }
        });

        pushSlice(sliceFrom, loc.end);

        return linesModule.concat(toConcat);
    };
}
exports.Patcher = Patcher;

var Pp = Patcher.prototype;

Pp.tryToReprintComments = function(newNode, oldNode, print) {
    var patcher = this;

    if (!newNode.comments &&
        !oldNode.comments) {
        // We were (vacuously) able to reprint all the comments!
        return true;
    }

    var newPath = FastPath.from(newNode);
    var oldPath = FastPath.from(oldNode);

    newPath.stack.push("comments", getSurroundingComments(newNode));
    oldPath.stack.push("comments", getSurroundingComments(oldNode));

    var reprints = [];
    var ableToReprintComments =
        findArrayReprints(newPath, oldPath, reprints);

    // No need to pop anything from newPath.stack or oldPath.stack, since
    // newPath and oldPath are fresh local variables.

    if (ableToReprintComments && reprints.length > 0) {
        reprints.forEach(function(reprint) {
            var oldComment = reprint.oldPath.getValue();
            assert.ok(oldComment.leading || oldComment.trailing);
            patcher.replace(
                oldComment.loc,
                // Comments can't have .comments, so it doesn't matter
                // whether we print with comments or without.
                print(reprint.newPath).indentTail(oldComment.loc.indent)
            );
        });
    }

    return ableToReprintComments;
};

// Get all comments that are either leading or trailing, ignoring any
// comments that occur inside node.loc. Returns an empty array for nodes
// with no leading or trailing comments.
function getSurroundingComments(node) {
    var result = [];
    if (node.comments &&
        node.comments.length > 0) {
        node.comments.forEach(function(comment) {
            if (comment.leading || comment.trailing) {
                result.push(comment);
            }
        });
    }
    return result;
}

Pp.deleteComments = function(node) {
    if (!node.comments) {
        return;
    }

    var patcher = this;

    node.comments.forEach(function(comment) {
        if (comment.leading) {
            // Delete leading comments along with any trailing whitespace
            // they might have.
            patcher.replace({
                start: comment.loc.start,
                end: node.loc.lines.skipSpaces(
                    comment.loc.end, false, false)
            }, "");

        } else if (comment.trailing) {
            // Delete trailing comments along with any leading whitespace
            // they might have.
            patcher.replace({
                start: node.loc.lines.skipSpaces(
                    comment.loc.start, true, false),
                end: comment.loc.end
            }, "");
        }
    });
};

exports.getReprinter = function(path) {
    assert.ok(path instanceof FastPath);

    // Make sure that this path refers specifically to a Node, rather than
    // some non-Node subproperty of a Node.
    var node = path.getValue();
    if (!Printable.check(node))
        return;

    var orig = node.original;
    var origLoc = orig && orig.loc;
    var lines = origLoc && origLoc.lines;
    var reprints = [];

    if (!lines || !findReprints(path, reprints))
        return;

    return function(print) {
        var patcher = new Patcher(lines);

        reprints.forEach(function(reprint) {
            var newNode = reprint.newPath.getValue();
            var oldNode = reprint.oldPath.getValue();

            SourceLocation.assert(oldNode.loc, true);

            var needToPrintNewPathWithComments =
                !patcher.tryToReprintComments(newNode, oldNode, print)

            if (needToPrintNewPathWithComments) {
                // Since we were not able to preserve all leading/trailing
                // comments, we delete oldNode's comments, print newPath
                // with comments, and then patch the resulting lines where
                // oldNode used to be.
                patcher.deleteComments(oldNode);
            }

            var pos = util.copyPos(oldNode.loc.start);
            var needsLeadingSpace = lines.prevPos(pos) &&
                riskyAdjoiningCharExp.test(lines.charAt(pos));

            var newLines = print(
                reprint.newPath,
                needToPrintNewPathWithComments
            ).indentTail(oldNode.loc.indent);

            var needsTrailingSpace =
                riskyAdjoiningCharExp.test(lines.charAt(oldNode.loc.end));

            // If we try to replace the argument of a ReturnStatement like
            // return"asdf" with e.g. a literal null expression, we run
            // the risk of ending up with returnnull, so we need to add an
            // extra leading space in situations where that might
            // happen. Likewise for "asdf"in obj. See #170.
            if (needsLeadingSpace || needsTrailingSpace) {
                var newParts = [];
                needsLeadingSpace && newParts.push(" ");
                newParts.push(newLines);
                needsTrailingSpace && newParts.push(" ");
                newLines = linesModule.concat(newParts);
            }

            patcher.replace(oldNode.loc, newLines);
        });

        // Recall that origLoc is the .loc of an ancestor node that is
        // guaranteed to contain all the reprinted nodes and comments.
        return patcher.get(origLoc).indentTail(-orig.loc.indent);
    };
};

function findReprints(newPath, reprints) {
    var newNode = newPath.getValue();
    Printable.assert(newNode);

    var oldNode = newNode.original;
    Printable.assert(oldNode);

    assert.deepEqual(reprints, []);

    if (newNode.type !== oldNode.type) {
        return false;
    }

    var oldPath = new FastPath(oldNode);
    var canReprint = findChildReprints(newPath, oldPath, reprints);

    if (!canReprint) {
        // Make absolutely sure the calling code does not attempt to reprint
        // any nodes.
        reprints.length = 0;
    }

    return canReprint;
}

function findAnyReprints(newPath, oldPath, reprints) {
    var newNode = newPath.getValue();
    var oldNode = oldPath.getValue();

    if (newNode === oldNode)
        return true;

    if (isArray.check(newNode))
        return findArrayReprints(newPath, oldPath, reprints);

    if (isObject.check(newNode))
        return findObjectReprints(newPath, oldPath, reprints);

    return false;
}

function findArrayReprints(newPath, oldPath, reprints) {
    var newNode = newPath.getValue();
    var oldNode = oldPath.getValue();
    isArray.assert(newNode);
    var len = newNode.length;

    if (!(isArray.check(oldNode) &&
          oldNode.length === len))
        return false;

    for (var i = 0; i < len; ++i) {
        newPath.stack.push(i, newNode[i]);
        oldPath.stack.push(i, oldNode[i]);
        var canReprint = findAnyReprints(newPath, oldPath, reprints);
        newPath.stack.length -= 2;
        oldPath.stack.length -= 2;
        if (!canReprint) {
            return false;
        }
    }

    return true;
}

function findObjectReprints(newPath, oldPath, reprints) {
    var newNode = newPath.getValue();
    isObject.assert(newNode);

    if (newNode.original === null) {
        // If newNode.original node was set to null, reprint the node.
        return false;
    }

    var oldNode = oldPath.getValue();
    if (!isObject.check(oldNode))
        return false;

    if (Printable.check(newNode)) {
        if (!Printable.check(oldNode)) {
            return false;
        }

        // Here we need to decide whether the reprinted code for newNode
        // is appropriate for patching into the location of oldNode.

        if (newNode.type === oldNode.type) {
            var childReprints = [];

            if (findChildReprints(newPath, oldPath, childReprints)) {
                reprints.push.apply(reprints, childReprints);
            } else if (oldNode.loc) {
                // If we have no .loc information for oldNode, then we
                // won't be able to reprint it.
                reprints.push({
                    oldPath: oldPath.copy(),
                    newPath: newPath.copy()
                });
            } else {
                return false;
            }

            return true;
        }

        if (Expression.check(newNode) &&
            Expression.check(oldNode) &&
            // If we have no .loc information for oldNode, then we won't
            // be able to reprint it.
            oldNode.loc) {

            // If both nodes are subtypes of Expression, then we should be
            // able to fill the location occupied by the old node with
            // code printed for the new node with no ill consequences.
            reprints.push({
                oldPath: oldPath.copy(),
                newPath: newPath.copy()
            });

            return true;
        }

        // The nodes have different types, and at least one of the types
        // is not a subtype of the Expression type, so we cannot safely
        // assume the nodes are syntactically interchangeable.
        return false;
    }

    return findChildReprints(newPath, oldPath, reprints);
}

// This object is reused in hasOpeningParen and hasClosingParen to avoid
// having to allocate a temporary object.
var reusablePos = { line: 1, column: 0 };
var nonSpaceExp = /\S/;

function hasOpeningParen(oldPath) {
    var oldNode = oldPath.getValue();
    var loc = oldNode.loc;
    var lines = loc && loc.lines;

    if (lines) {
        var pos = reusablePos;
        pos.line = loc.start.line;
        pos.column = loc.start.column;

        while (lines.prevPos(pos)) {
            var ch = lines.charAt(pos);

            if (ch === "(") {
                // If we found an opening parenthesis but it occurred before
                // the start of the original subtree for this reprinting, then
                // we must not return true for hasOpeningParen(oldPath).
                return comparePos(oldPath.getRootValue().loc.start, pos) <= 0;
            }

            if (nonSpaceExp.test(ch)) {
                return false;
            }
        }
    }

    return false;
}

function hasClosingParen(oldPath) {
    var oldNode = oldPath.getValue();
    var loc = oldNode.loc;
    var lines = loc && loc.lines;

    if (lines) {
        var pos = reusablePos;
        pos.line = loc.end.line;
        pos.column = loc.end.column;

        do {
            var ch = lines.charAt(pos);

            if (ch === ")") {
                // If we found a closing parenthesis but it occurred after the
                // end of the original subtree for this reprinting, then we
                // must not return true for hasClosingParen(oldPath).
                return comparePos(pos, oldPath.getRootValue().loc.end) <= 0;
            }

            if (nonSpaceExp.test(ch)) {
                return false;
            }

        } while (lines.nextPos(pos));
    }

    return false;
}

function hasParens(oldPath) {
    // This logic can technically be fooled if the node has parentheses
    // but there are comments intervening between the parentheses and the
    // node. In such cases the node will be harmlessly wrapped in an
    // additional layer of parentheses.
    return hasOpeningParen(oldPath) && hasClosingParen(oldPath);
}

function findChildReprints(newPath, oldPath, reprints) {
    var newNode = newPath.getValue();
    var oldNode = oldPath.getValue();

    isObject.assert(newNode);
    isObject.assert(oldNode);

    if (newNode.original === null) {
        // If newNode.original node was set to null, reprint the node.
        return false;
    }

    // If this type of node cannot come lexically first in its enclosing
    // statement (e.g. a function expression or object literal), and it
    // seems to be doing so, then the only way we can ignore this problem
    // and save ourselves from falling back to the pretty printer is if an
    // opening parenthesis happens to precede the node.  For example,
    // (function(){ ... }()); does not need to be reprinted, even though
    // the FunctionExpression comes lexically first in the enclosing
    // ExpressionStatement and fails the hasParens test, because the
    // parent CallExpression passes the hasParens test. If we relied on
    // the path.needsParens() && !hasParens(oldNode) check below, the
    // absence of a closing parenthesis after the FunctionExpression would
    // trigger pretty-printing unnecessarily.
    if (!newPath.canBeFirstInStatement() &&
        newPath.firstInStatement() &&
        !hasOpeningParen(oldPath))
        return false;

    // If this node needs parentheses and will not be wrapped with
    // parentheses when reprinted, then return false to skip reprinting
    // and let it be printed generically.
    if (newPath.needsParens(true) && !hasParens(oldPath)) {
        return false;
    }

    for (var k in util.getUnionOfKeys(newNode, oldNode)) {
        if (k === "loc")
            continue;

        newPath.stack.push(k, types.getFieldValue(newNode, k));
        oldPath.stack.push(k, types.getFieldValue(oldNode, k));
        var canReprint = findAnyReprints(newPath, oldPath, reprints);
        newPath.stack.length -= 2;
        oldPath.stack.length -= 2;

        if (!canReprint) {
            return false;
        }
    }

    return true;
}