feat!: ComposablePass trait allowing sequencing and validation

[acl-cqc]

Currently We have several "passes": monomorphization, dead function removal, constant folding. Each has its own code to allow setting a validation level (before and after that pass).

This PR adds the ability chain (sequence) passes;, and to add validation before+after any pass or sequence; and commons up validation code. The top-level constant_fold_pass (etc.) functions are left as wrappers that do a single pass with validation only in test.

I've left ConstFoldPass as always including DCE, but an alternative could be to return a sequence of the two - ATM that means a tuple (ConstFoldPass, DeadCodeElimPass).

I also wondered about including a method add_entry_point in ComposablePass (e.g. for ConstFoldPass, that means with_inputs but no inputs, i.e. all Top). I feel this is not applicable to all passes, but near enough. This could be done in a later PR but add_entry_point would need a no-op default for that to be a non-breaking change. So if we wouldn't be happy with the no-op default then I could just add it here...

Finally...docs are extremely minimal ATM (this is hugr-passes), I am hoping that most of this is reasonably obvious (it doesn't really do a lot!), but please flag anything you think is particularly in need of a doc comment!

BREAKING CHANGE: quite a lot of calls to current pass routines will break, specific cases include (a) with_validation_level should be done by wrapping a ValidatingPass around the receiver; (b) XXXPass::run() requires use ...ComposablePass (however, such calls will cease to do any validation).

closes #1832

[hugrbot]

This PR contains breaking changes to the public Rust API.

cargo-semver-checks summary

--- failure enum_missing: pub enum removed or renamed ---

Description:
A publicly-visible enum cannot be imported by its prior path. A `pub use` may have been removed, or the enum itself may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.40.0/src/lints/enum_missing.ron

Failed in:
enum hugr_passes::validation::ValidationLevel, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/validation.rs:16
enum hugr_passes::validation::ValidatePassError, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/validation.rs:28
enum hugr_passes::MonomorphizeError, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/monomorphize.rs:282

--- failure enum_variant_missing: pub enum variant removed or renamed ---

Description:
A publicly-visible enum has at least one variant that is no longer available under its prior name. It may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.40.0/src/lints/enum_variant_missing.ron

Failed in:
variant ConstFoldError::ValidationError, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/const_fold.rs:47
variant RemoveDeadFuncsError::ValidationError, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/dead_funcs.rs:31

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.40.0/src/lints/inherent_method_missing.ron

Failed in:
RemoveDeadFuncsPass::validation_level, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/dead_funcs.rs:73
DeadCodeElimPass::validation_level, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/dead_code.rs:91
DeadCodeElimPass::validation_level, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/dead_code.rs:91
MonomorphizePass::validation_level, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/monomorphize.rs:290
ConstantFoldPass::validation_level, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/const_fold.rs:57

--- failure method_requires_different_generic_type_params: method now requires a different number of generic type parameters ---

Description:
A method now requires a different number of generic type parameters than it used to. Uses of this method that supplied the previous number of generic types will be broken.
      ref: https://doc.rust-lang.org/reference/items/generics.html
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.40.0/src/lints/method_requires_different_generic_type_params.ron

Failed in:
hugr_passes::RemoveDeadFuncsPass::run takes 0 generic types instead of 1, in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-passes/src/dead_funcs.rs:87
hugr_passes::MonomorphizePass::run takes 0 generic types instead of 1, in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-passes/src/monomorphize.rs:263
hugr_passes::const_fold::ConstantFoldPass::run takes 0 generic types instead of 1, in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-passes/src/const_fold.rs:97

--- failure module_missing: pub module removed or renamed ---

Description:
A publicly-visible module cannot be imported by its prior path. A `pub use` may have been removed, or the module may have been renamed, removed, or made non-public.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.40.0/src/lints/module_missing.ron

Failed in:
mod hugr_passes::validation, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-passes/src/validation.rs:1

[codecov]

Codecov Report

Attention: Patch coverage is 88.39779% with 21 lines in your changes missing coverage. Please review.

Project coverage is 83.76%. Comparing base (fdcd48a) to head (80cedfc).
Report is 14 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-passes/src/composable.rs	88.70%	10 Missing and 4 partials ⚠️
hugr-passes/src/monomorphize.rs	77.77%	1 Missing and 3 partials ⚠️
hugr-passes/src/const_fold.rs	60.00%	1 Missing and 1 partial ⚠️
hugr-passes/src/dead_funcs.rs	95.65%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1895      +/-   ##
==========================================
+ Coverage   83.74%   83.76%   +0.02%     
==========================================
  Files         204      208       +4     
  Lines       38585    39015     +430     
  Branches    35395    35723     +328     
==========================================
+ Hits        32312    32680     +368     
- Misses       4472     4498      +26     
- Partials     1801     1837      +36     

Flag	Coverage Δ
python	∅ <ø> (∅)
rust	∅ <88.39%> (∅)

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[acl-cqc]

The other way to do this is

fn sequence_before<P2: ComposablePass>(self, other: P2) -> impl ComposablePass<Err = Self::Err>
   where P2::Err : Into<Self::Err>

(and similarly sequence_after) which avoids what may be a common-case use of map_err (i.e. with Into).

However, Infallible doesn't implement Into, so it's probably not much of a win. (I could add sequence_infallible(self, other: ComposablePass<Err=Infallible>) I guess, but would then want that before/after versions of that too)

[cqc-alec]

Looks good! I do think some more docs would be good. Regarding the suggestion to add add_entry_point -- does it mean to apply the pass to everything below that point in the hierarchy but not above it? I think that sounds reasonable.

[acl-cqc]

Breaking, so will leave merging until after end March