Collection of `filterFilter` related issues (with regard to #9757)

[gkalpak]

Following #9757, I tried to gather open filterFilter-related issues (bugs, PRs, feature requests) and investigate if/how they relate to #9757 (e.g. if they are resolved or contain test-cases that can be incorporated etc).

Listing my "findings" here to avoid duplication of effort.

_{Kudos to @Narretz for the idea (#9757 (comment)) 😃.}

** Updated by Pete with what is left **

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tl;dr

PRs:

• PRs that should be probably closed anyway: fix(filterFilter): comparator should return true if deep object key is undefined #6623
• PRs that will need to get updated if fix(filterFilter): correctly handle deep expression objects #9757 lands: feat(filter): allow filtering of an object #5451, feat(filterFilter): support filterFilter for object literal collection #6695, docs(filter): clarify what filter matches against #8750
• PRs that will be obsolete if fix(filterFilter): correctly handle deep expression objects #9757 lands: fix(filterFilter) deeply-nested predicate objects + multiple conditions were not giving expected results #7329

Bugs / Feature Requests:

• Issues that should be probably closed anyway: Null filter not returning anything: filter:{category:null}" #1780, Why does filterFilter take out null values when compared with '' in 1.2.x  #5055, Filters for nested objects not working #6222, Use search.$ in filter will result in Call stack exceeded error if the objects have properties that self reference #6655
• Issues that are irrelevant to fix(filterFilter): correctly handle deep expression objects #9757: [filter] allow object maps along with arrays #2694, Implement filtering on object-based ng-repeat #6490, filter and orderBy should also work with objects in ngRepeat #8458
• Issues that will be resolved if fix(filterFilter): correctly handle deep expression objects #9757 lands: FilterFilter nested expression support renders strict option useless #7323, $filter('filter')(array, expression) does not work with more than one nested property #9698, filter doesn't work when methods are added to Object.prototype #9984

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Bugs / Feature Requests

• [Implement filtering on object-based ng-repeat #6490: Implement filtering on object-based ng-repeat][6490]
  This is about adding support for filtering objects (not only arrays) for use with ngRepeat.
  Irrelevant to fix(filterFilter): correctly handle deep expression objects #9757.
  
• [Use search.$ in filter will result in Call stack exceeded error if the objects have properties that self reference #6655: Call stack exceeded error on objects with circular references][6655]
  Based on the conversation (and the referenced Fix(filter): Filter objects with circular references #6319) it seems to have been decided not to support objects with circular references.
  Should be probably closed.
  
• [filter and orderBy should also work with objects in ngRepeat #8458: filterFilter and orderByFilter should also work with objects][8458]
  This is about adding support for filtering objects (not only arrays).
  Irrelevant to fix(filterFilter): correctly handle deep expression objects #9757.
  

[btford]

This is lovely. Thanks so much @gkalpak.

[albertboada]

WOW, fantastic job on compiling all the filterFilter issues. True story for #7329 👍

[gkalpak]

(Added info regarding #9984.)

[Narretz]

@gkalpak Did we handle all of these?

[gkalpak]

@Narretz, I don't. think so :(

#9757 has landed and the related issues/PRs have been closed, but there are issues in this list that are unrelated to #9757 (e.g. ones that should (imo) be closed), which aren't handled yet.

[petebacondarwin]

So we are left with #6490 #6655 and #8458.