Raise error on variable use before write

[fangyi-zhou]

Closes #15, #248

This change adds additional checks when building bindings, so that
variables that are used before initialised are correctly flagged as
errors.

Currently, we error on uninitialised variables by checking their flow
style. If the flow style is uninitialised or partially uninitialised, an
error is generated. When no flow style information is obtainable (which
is the case for use before write), a default "other" flow style value is
returned.

In this diff, we perform additional checks before returning a default
"other" value. By looking up the scopes for static information for
variables, we can correctly detect if a variable is declared in an upper
scope or in the current scope, and return "uninitialised" flow style
when the variable is used before write.

When doing so, we need to consider the special case for type usages,
so that name resolutions in types do not fail.

Help needed:
There's a failing test that I need some help: test::flow::test_assert_not_in_flow

testcase!(
    test_assert_not_in_flow,
    r#"
from typing import assert_type, Literal
if 0.1:
    vari = "test"
    raise SystemExit
assert_type(vari, Literal["test"])   <-- Shall we raise an error here?
"#,
);

[stroxler]

This looks pretty good to me, thanks for the PR!

There are a lot of test failures I can't explain easily - I wonder if you just need a rebase? I see compile errors on dataclasses which doesn't seem to be changed here so that's my best guess

After a rebase, if you publish I could work on getting it merged

[fangyi-zhou]

Rebased and addressed your inline comments. There should be only one test failing (which is the one I linked in the PR description)

[yangdanny97]

Thanks!

For the failing test case test_assert_not_in_flow, I think raising an error there would be correct.

[fangyi-zhou]

Thanks!

For the failing test case test_assert_not_in_flow, I think raising an error there would be correct.

If it's not too inconvenient, could you fix that for me during the import? Thanks!

[facebook-github-bot]

@stroxler has imported this pull request. If you are a Meta employee, you can view this in D78496802.

[stroxler]

This may have to wait a day or two, we have some internal infra issues and I can't import the PR right now

[facebook-github-bot]

@stroxler has imported this pull request. If you are a Meta employee, you can view this in D78496802.

[facebook-github-bot]

@stroxler has imported this pull request. If you are a Meta employee, you can view this in D78496802.

[stroxler]

Looks good to me, I'll work on getting it merged. Thanks!

[fangyi-zhou]

Thanks a lot! @stroxler

[facebook-github-bot]

@stroxler merged this pull request in 600c8f1.