feat: Update CFG checker to use new diagnostics

[mark-koch]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.50649% with 5 lines in your changes missing coverage. Please review.

Project coverage is 91.77%. Comparing base (8134a85) to head (6773c2b).
Report is 2 commits behind head on feat/diagnostics.

Files with missing lines	Patch %	Lines
guppylang/definition/function.py	0.00%	3 Missing ⚠️
guppylang/checker/cfg_checker.py	96.61%	2 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           feat/diagnostics     #589      +/-   ##
====================================================
+ Coverage             91.73%   91.77%   +0.04%     
====================================================
  Files                    61       61              
  Lines                  6509     6579      +70     
====================================================
+ Hits                   5971     6038      +67     
- Misses                  538      541       +3     

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[ss2165]

These are some very cool errors!
Some queries about falsy loops and compound predicate expressions

[ss2165]

to my eye this looks like if x False rather than if x and (z := y + 1) is False ...

[mark-koch]

I think the message is correct:

If x were true then z would be defined because of the walrus assignment even if the whole thing tends out to be false.

If x is false, then z is not defined because and short circuits

[mark-koch]

This is the test:

@guppy
def foo(x: bool, y: int) -> int:
    if x and (z := y + 1):
        return z
    else:
        return z

[ss2165]

that makes sense! thanks

[ss2165]

this is a bit confusing, do we need to say "Falsey"...?

[mark-koch]

I like the idea of differentiating between bools and values that are truthy. The problem is that we can no longer make this distinction here since we already inserted an implicit call to __bool__.

An additional problem is that for loops are desugared to

iter = xs.__iter__()
while True:
   b, iter = iter.__hasnext__()
   if b:
      x, it = iter.__next__()
   else:
      break
iter.__end__()

and the message actually points to the while True bit which actually is a bool.

Created issues #591 and #592 to figure out how to solve this

[ss2165]

same as previous query