Implement support for break statement

[cburgdorf]

What was wrong?

We don't support break statements yet.

How was it fixed?

1. Added a new BlockScopeType to BlockScope that can be one of Function, IfElse or Loop.
2. Added pub fn inherits_type(&self, typ: BlockScopeType) -> bool to BlockScope to be able to tell if certain statements (e.g. break, continue) can be used within the current scope or not.
3. Semantic pass checks with inherits_type if placement is ok and returns SemanticError::BreakWithoutLoop if not
4. Mapper pass maps break to YUL

[codecov-io]

Codecov Report

Merging #125 (d279f2e) into master (05b6f3d) will increase coverage by 0.00%.
The diff coverage is 84.00%.

@@           Coverage Diff           @@
##           master     #125   +/-   ##
=======================================
  Coverage   84.38%   84.39%           
=======================================
  Files          40       40           
  Lines        2556     2596   +40     
=======================================
+ Hits         2157     2191   +34     
- Misses        399      405    +6     

Impacted Files	Coverage Δ
compiler/src/yul/mappers/functions.rs	0.00% <0.00%> (ø)
semantics/src/traversal/functions.rs	46.87% <0.00%> (-0.50%)	⬇️
semantics/src/namespace/scopes.rs	92.66% <93.33%> (-0.20%)	⬇️
compiler/src/abi/elements.rs	89.47% <0.00%> (-1.76%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 05b6f3d...d279f2e. Read the comment docs.

[g-r-a-n-t]

👍

[g-r-a-n-t]

I had been using Rc::clone(&scope), since that's what's used in the API docs for Rc: https://doc.rust-lang.org/std/rc/struct.Rc.html.

Both of these do the same thing, of course, and I don't have a strong opinion about which method we should use to call clone, but I think we should be consistent.

[cburgdorf]

Thanks for bringing this up. I wasn't aware that there was a good reason for the the more verbose syntax. I looked it up and RC::clone(&ptr) is indeed the preferred syntax. The reason for that is to make it clear what the clone is about since clone is a very vaguely defined action in Rust. In this case it is just increasing the reference counter whereas e.g. cloning a Vec<T> can cause quite a bit of memory getting copied.

References:

https://github.com/nical/rfcs/blob/rc-newref-clone/text/0000-rc-newref-clone.md
rust-lang/rust#42137 (comment)

I'm going to merge this as is and send a follow up PR to rewrite all occurrences with the idiomatic syntax.

[cburgdorf]

Updated all usage in this PR #126