feat!: Handle CallIndirect in constant folding

[acl-cqc]

• Extend ValueHandle with a node pointer into the containing Hugr - the previous approach of handling LoadFunction by stealing the body of the loaded function, will not work for functions with incoming static edges (i.e. from other functions/constants).
• Add new interpret_call_indirect method to trait DFContext (alongside interpret_leaf_op), again defaulting to { }
• Implement for ConstFoldContext by a complete recursion (i.e. when the called function is known).

• TODO: tests!
• This recursion may be expensive (and seems more than we do for calls - multiple CallIndirects to the same function will each get their own analysis, without aliasing, whereas multiple Calls to the same function get corresponding arguments/intermediates joined together). Should be put it under a switch?

BREAKING CHANGE: mod value_handle (containing ValueHandle and HashedConst) is no longer pub.

[codecov]

Codecov Report

Attention: Patch coverage is 3.33333% with 58 lines in your changes missing coverage. Please review.

Project coverage is 83.21%. Comparing base (6fff648) to head (482a435).
Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-passes/src/const_fold.rs	0.00%	39 Missing ⚠️
hugr-passes/src/dataflow.rs	0.00%	7 Missing ⚠️
hugr-passes/src/const_fold/value_handle.rs	25.00%	6 Missing ⚠️
hugr-passes/src/dataflow/datalog.rs	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2046      +/-   ##
==========================================
+ Coverage   83.17%   83.21%   +0.04%     
==========================================
  Files         215      217       +2     
  Lines       41312    41910     +598     
  Branches    37526    38124     +598     
==========================================
+ Hits        34362    34877     +515     
- Misses       5006     5079      +73     
- Partials     1944     1954      +10     

Flag	Coverage Δ
python	85.92% <ø> (ø)
rust	82.95% <3.33%> (+0.05%)	⬆️

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[hugrbot]

This PR contains breaking changes to the public Rust API.

cargo-semver-checks summary

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.40.0/src/lints/enum_variant_added.ron

Failed in:
variant ValueHandle:NodeRef in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-passes/src/const_fold/value_handle.rs:58

[aborgna-q]

Looks great, just missing the tests.

This recursion may be expensive (...). Should be put it under a switch?

You mean to enabling/disabling callindirect folding altogether?
I'd say we can wait and see if it's necessary, but I guess we could add a ConstFoldConfig struct here since we're breaking the API already.

[aborgna-q]

It's quite annoying that we have to make this a breaking change.
It looks like even leaving this as public wouldn't help, since ValueHandle is not non_exhaustive and added new fields -.-

Is it OK to wait in merging this PR until we accumulate other breaking changes?

[acl-cqc]

Yeah, I was hiding that because I thought that's the way that it should have been, would have avoided this being a breaking change now...

How urgent....I was gonna say, the bit we need first is the constant_fold_with_hugr and that's non-breaking so I can break that out and leave the rest as a demo (just tests that the ValueHandle/CallIndirect works would confirm we can do the same approach in/for BRAT).

However....now I realize we need to get the ValueHandle::NodeRef into the BRAT-specific constant-folding code. At present extension-provided constant-folders only get Hugr Values, so rather than adding constant_fold_with_hugr I think I need some kind of plugin interface to the constant-folding pass that lets us get at those ValueHandles after all. So I think I'll have to restore pubness and figure out what the plugin interface is.

[acl-cqc]

Closing in favour of #2059