test: Use assert_matches! less

[acl-cqc]

There are downsides to assert_matches!:

• Extra dependency/import
• Reduced linting - see several cases here where converting to assert!(matches!(...)) lead to clippy noticing that the match could be converted to .is_ok() or .is_some()
• Increased chance of accidents, see test: fix some bad assert_matches #1006 (preliminary to this)

Hence, this PR adopts the policy of "use assert_matches only when it's useful". Specifically, that means only when we can use

assert_matches!(SUBJECT, PATTERN => assert!(EXPR))

(and while we're at it, where EXPR is an equality, use assert_eq!), rather than

assert!(matches!(SUBJECT, PATTERN if EXPR))

because the former gives better error messages in case of failure.

(This is quite a small advantage, and noting the increased chance of accidents, one could also say - let's not use assert_matches at all....I'd be happy to do that, too.)

[codecov]

Codecov Report

Attention: Patch coverage is 45.16129% with 34 lines in your changes are missing coverage. Please review.

Project coverage is 85.89%. Comparing base (e5fd315) to head (33f8515).

Files	Patch %	Lines
hugr/src/hugr/validate/test.rs	8.33%	0 Missing and 11 partials ⚠️
hugr/src/extension/infer/test.rs	14.28%	0 Missing and 6 partials ⚠️
hugr/src/std_extensions/arithmetic/int_types.rs	0.00%	0 Missing and 5 partials ⚠️
hugr/src/builder/dataflow.rs	33.33%	0 Missing and 4 partials ⚠️
hugr/src/builder/conditional.rs	33.33%	0 Missing and 2 partials ⚠️
hugr/src/hugr/views/sibling_subgraph.rs	66.66%	0 Missing and 2 partials ⚠️
hugr/src/ops/constant.rs	50.00%	0 Missing and 2 partials ⚠️
hugr/src/builder/cfg.rs	66.66%	0 Missing and 1 partial ⚠️
hugr/src/hugr/rewrite/outline_cfg.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1004      +/-   ##
==========================================
+ Coverage   85.72%   85.89%   +0.17%     
==========================================
  Files          79       79              
  Lines       14531    14558      +27     
  Branches    14531    14558      +27     
==========================================
+ Hits        12456    12505      +49     
+ Misses       1428     1393      -35     
- Partials      647      660      +13     

Flag	Coverage Δ
rust	85.89% <45.16%> (+0.17%)	⬆️

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[aborgna-q]

The value of assert_matches is in the error messages. Compare

let x = None;
assert!(matches!(x, Some(42)));
// thread 'test::test_assert' panicked at src/lib.rs:14:9:
// assertion failed: matches!(x, Some(42))
// note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

with

let x = None;
assert_matches!(x, Some(42));
// thread 'test::test_matches' panicked at src/lib.rs:8:9:
// assertion failed at src/lib.rs:8: `(value does not match pattern)`
//   value: None
// pattern: Some(42)

In this case, matching against a pattern instead of doing .is_ok() is the intended behaviour.

I agree that adding statements on the matched branches is error-prone. I'm happy with banning those.

[aborgna-q]

I'm closing this PR since seem to have agreed on the status quo.
Feel free to reopen it if you want to continue the discussion.