URI.allLocations leads to endless loop if URI has own schema

[corneliusludmann]

Description

When you create an URI object with an individual scheme (not file:), calling .allLocations leads to an endless loop. (Creating an URI with new URI('foo.txt') assumes an absolute path /foo.txt which prevents the problem described below.) An URI with own scheme is used in user-preferences-provider.ts, for example.

Reproduction Steps

Execute the following code:

const allLocations = new URI().withScheme('foo').withPath('foobar.txt').allLocations;

will results in an endless loop at this code position: https://github.com/eclipse-theia/theia/blob/master/packages/core/src/common/uri.ts#L54

let location: URI = this;
while (!location.path.isRoot) {
    locations.push(location);
    location = location.parent;
}

The reason is that location is equal to location.parent and location.path.isRoot === false.

In my opinion, the root of this problems lies in Path.dir which returns this when there is no path separator (see https://github.com/eclipse-theia/theia/blob/master/packages/core/src/common/path.ts#L124). I think, it would be more intuitive if undefined or so will returned in this case. Or we need something like hasParent to distinguish this situation because the isRoot check is not sufficient here.

To fix this with as little potential side effects as possible, I suggest changing the while condition as follows:

let location: URI = this;
while (!location.path.isRoot && location.toString() !== location.parent.toString()) {
    locations.push(location);
    location = location.parent;
}

[corneliusludmann]

Added PR #6378 that implements the Path.hasParent solution.