Mongodb-odm: Doctrine\MongoDB\Query\Expr::popFirst is incorrect

[juliusxyg]

Bug Report

| Q | A
|------------ | ------
| BC Break | no
| Version | 1.6.2

Summary

Two methods
Doctrine\MongoDB\Query\Expr::popFirst()
Doctrine\MongoDB\Query\Expr::popLast()

use wrong $pop value.

Current behavior

according to mongodb manual

The $pop operator removes the first or last element of an array. Pass $pop a value of -1 to remove the first element of an array and 1 to remove the last element in an array.

pop first is -1, pop last is 1,

in the code is just reversed.

[alcaeus]

Moved to the 2.0 line since that's the only bug fix to do in ODM. For 1.x, the error is in doctrine/mongodb and will be fixed in a separate release today. Thanks for the report!

[alcaeus]

doctrine/mongodb 1.6.3 was just released containing the fix for this issue. For 2.0 (the current master branch, #1831 will port the fix to ODM.

Since I was bored this morning, I decided to dig into the history of this bug:

It was introduced 8 years ago (May 2010) when a young developer added update methods to the ODM query object and made a tiny mistake in the documentation (First is 1 and last is -1): https://github.com/doctrine/mongodb-odm/commit/795dc997e67e801c1352e5e450a349c2701ad4cb#diff-d9cea82dc18423811aa7d0cc84fdbe25R673
A few hours later, the same developer would then refactor the pop method into popFirst and popLast, incorporating their own documentation mistake and creating the wrong behavior you found: https://github.com/doctrine/mongodb-odm/commit/063286144475cd5431824394ab61560ae93552e0#diff-d9cea82dc18423811aa7d0cc84fdbe25R714.
This was released as ODM 1.0.0-BETA4 in August 2010, which would be the first version to contain the bug.
From then, the issue made its way to the new doctrine/mongodb library in December of 2010 later to be released as 1.0.0-BETA1: https://github.com/doctrine/mongodb/commit/98e70d36b6ab9ab48970e3251c26df305b29f890#diff-0a4ad011a43c676e967fac2188a7ee0fR291
The bug had its big homecoming 7 years later in December 2017 when we dropped doctrine/mongodb in favour of the MongoDB PHP library: https://github.com/doctrine/mongodb-odm/pull/1553 (I would link the exact line, but GitHub really doesn't like large commits and pull requests).

So, again, thank you for finding and reporting an 8 year old bug that caused wrong data to be removed - you were either the first person to hit it or the first to care enough about their data to report it as a bug. I hope you enjoyed that little trip down the long and colourful history of this bug.