Implement with_hasher adaptors

[424ever]

Closes #998

Implementations for the following methods:

• duplicates_with_hasher
• duplicates_by_with_hasher
• unique_with_hasher
• unique_by_with_hasher
• all_unique_with_hasher
• into_group_map_with_hasher
• into_group_map_by_with_hasher
• into_grouping_map_with_hasher
• into_grouping_map_by_with_hasher
• counts_with_hasher
• counts_by_with_hasher

[jswrenn]

One small nit, but otherwise this LGTM.

[phimuemue]

Two nits:

• I'm a bit unhappy about duplicated tests. We can leave them as is and add a TODO that we'd ideally want to write all test cases once and apply them to both normal and _with_hasher functions automagically.

• (Possibly over-nitpicky:) Should we rely on the fact that RandomState is the default BuildHasher or should we extract it so that std can do whatever it wants and we just adapt it? Could be done as follows:

  trait THashMap {
      type BuildHasher;
  }
  impl<K, V, S> THashMap for std::collections::HashMap<K, V, S> {
      type BuildHasher = S;
  }
  type StdDefaultBuildHasher = <std::collections::HashMap<(), ()> as THashMap>::BuildHasher;
  
  

@jswrenn Feel free to proceed as you deem appropriate.

[codecov]

Codecov Report

❌ Patch coverage is 99.52830% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.02%. Comparing base (6814180) to head (eba2678).
⚠️ Report is 188 commits behind head on master.

Files with missing lines	Patch %	Lines
src/grouping_map.rs	95.45%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1007      +/-   ##
==========================================
- Coverage   94.38%   94.02%   -0.37%     
==========================================
  Files          48       51       +3     
  Lines        6665     6631      -34     
==========================================
- Hits         6291     6235      -56     
- Misses        374      396      +22     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jswrenn]

• Should we rely on the fact that RandomState is the default BuildHasher or should we extract it so that std can do whatever it wants and we just adapt it?

It would be a breaking change for Rust to change its default hasher, so we're fine to rely on RandomState directly.

[xtqqczze]

@424ever Are you planning to continue with this PR?

[424ever]

@424ever Are you planning to continue with this PR?

Sorry for the late reply. Yes, I'll rebase this and clean it up a bit

[424ever]

Do I need to do something about the failing semver checks? Those aren't in any files this PR touches.

[xtqqczze]

@phimuemue @jswrenn Can we get this in for 0.15?

[xtqqczze]

Do I need to do something about the failing semver checks?

The semver check failure is informational, and expected because there are changes to the public API.

[jswrenn]

@phimuemue @jswrenn Can we get this in for 0.15?

Yeah, sure! :)

[424ever]

Hi!

Unfortunately my graphics card died today so I probably can't respond to requests changes for at least a few days.

[xtqqczze]

@phimuemue @jswrenn Do you have any outstanding review comments?

[phimuemue]

@jswrenn tldr; I suggest we take this as is. Could you have a look and merge it?

@424ever Thanks for this. Looks clean and relatively straightforward. Please don't push additional changes on top of eba2678 - I'd like to avoid re-reviewing.

---

Once this is merged, we may come back and fine-tune:

• Documentation could be more uniform.
• "Delegating" functions could be more uniform.
• GroupingMap could go without S, and have a _with_hasher variant for each function.
• Tests check the interface, but not that the passed hasher is actually used inside.
• Something that automagically detects presence of _with_hasher-variant and compares it against its ordinary counterpart would be nice, but is hard to come up with.