relative() returns incorrect result

[devoncarew]

We're seeing a failure in flutter's tests (flutter/flutter#1709) which looks like a bug in path's relative() function:

from: /var/folders/00/0w978000h01000cxqpysvccm003j4x/T/flutter_toolsZUIVMq
to:   /Users/devoncarew/projects/flutter/flutter/packages

result = path.relative(to, from: from);

result: ../../../../../../Users/devoncarew/projects/flutter/flutter/packages

The relative result isn't correct. It's off by one in the number of times it should traverse up to the parent directory. From flutter_toolsZUIVMq it can only go up 5 times to /, but it has 6 ..'s in the relative result.

[devoncarew]

https://github.com/flutter/flutter/blob/master/packages/flutter_tools/lib/src/commands/create.dart#L131

[nex3]

This looks correct to me. It satisfies the invariant that p.join(from, p.relative(path, from: from)) refers to the same path as path.

import 'package:path/path.dart' as p;

void main() {
  var from = "/var/folders/00/0w978000h01000cxqpysvccm003j4x/T/flutter_toolsZUIVMq";
  var path = "/Users/devoncarew/projects/flutter/flutter/packages";

  print(p.normalize(from, p.join(p.relative(path, from: from))));
  // => /Users/devoncarew/projects/flutter/flutter/packages
}

Keep in mind that the from argument takes the place of the current directory. So if flutter_toolsZUIVMq is a file and you want a relative path that is valid within that file, from should be /var/folders/00/0w978000h01000cxqpysvccm003j4x/T.

[devoncarew]

flutter_toolsZUIVMq is a directory - we're creating a pubspec file in there and trying to write a relative path from there to the flutter package. (flutter_toolsZUIVMq/pubspec.yaml)

[nex3]

In that case, the path you listed should work. I count six ..s, which matches the six path segments in from.

[devoncarew]

But from flutter_toolsZUIVMq, it's only 5 segments up.

What's odd is that this test works on linux. And it does look like the relative path being created in the pubspec is bad.

[nex3]

But from flutter_toolsZUIVMq, it's only 5 segments up.

Not if it's a directory and you're resolving a path inside it. You still have to .. up through flutter_toolsZUIVMq.

What's odd is that this test works on linux. And it does look like the relative path being created in the pubspec is bad.

I suspect the real issue here is OS X's symlinking of the /tmp directory. Relative paths that move up out of symlinked directories are unreliable; they can be resolved differently depending on what the resolving entity thinks the current working directory's path is.

[devoncarew]

Ah, something to look into. I'll see if canonicalizing the paths helps.