clippy: fix collapsible_match lint

[xtqqczze]

fix warn-by-default lint in Rust 1.95

https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.92%. Comparing base (6814180) to head (348e1ba).
⚠️ Report is 187 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1099      +/-   ##
==========================================
- Coverage   94.38%   93.92%   -0.47%     
==========================================
  Files          48       51       +3     
  Lines        6665     6466     -199     
==========================================
- Hits         6291     6073     -218     
- Misses        374      393      +19     

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[xtqqczze]

I fixed this manually because the Clippy suggestion introduced an error; issue reported: rust-lang/rust-clippy#16860.

[phimuemue]

Hi there, thanks for this, but oh Clippy...

@jswrenn I think we should avoid _-wildcard-patterns in match unless strictly necessary. They don't show the possible states explicitly. I'd even discourage them with Option/Result/other similarly well-known types (if only for consistency). Same applies to matches!/if let in my book.

My guideline for reasonably explicit code would be:

• No wildcards in match unless absolutely necessary. (Not even for simple types for consistency.)
• No matches!.
• Allow if let for Option.

imho we should bring our code to these standards, and - if Clippy complains too loudly - silence this particular lint.

[xtqqczze]

In these cases, we could replace the match with a single if let guard, e.g.:

            if let Some(old_key) = self.current_key.take() {
                if old_key != key {
                    self.current_key = Some(key);
                    first_elt = Some(elt);
                    break;
                }
            }

[phimuemue]

In these cases, we could replace the match with a single if let guard, e.g.:

Yes, please go with that.

[phimuemue]

Thank you!