Reject certain code that should return but doesn't

[cburgdorf]

What was wrong?

As described in #497 the following code does compile in master but should generate a user error instead. It needs to error because the code is missing a return statement since it is not guaranteed that the execution follows the arm of the if statement.

contract Foo:
    pub def bar(val: u256) -> u256:
        if val > 1:
            return 5

How was it fixed?

The check in all_paths_return_or_revert is wrong because it counts a missing else branch as if the code returns when clearly a missing else branch shouldn't indicate such thing.

[cburgdorf]

This was an extra error in the test file that I think we didn't intent to test for here

[codecov-commenter]

Codecov Report

Merging #502 (f4ddda2) into master (71a2430) will decrease coverage by 0.02%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #502      +/-   ##
==========================================
- Coverage   87.72%   87.69%   -0.03%     
==========================================
  Files          80       80              
  Lines        5272     5276       +4     
==========================================
+ Hits         4625     4627       +2     
- Misses        647      649       +2     

Impacted Files	Coverage Δ
crates/test-files/src/lib.rs	50.00% <50.00%> (ø)
crates/analyzer/src/traversal/functions.rs	91.17% <100.00%> (ø)

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[g-r-a-n-t]

we could just get rid of the is_empty check, as all_paths_return_or_revert(or_else) will return false for an empty vec

[cburgdorf]

Ah sure, I'll get that updated 👍