Rewrite file-sniffer analysis

[angelikatyborska]

Resolves #407

Originally this PR was called:

Rewrite file-sniffer analysis (assert_call should also find calls in function heads)

After a deep dive, I realized that assert_call is already capable of finding calls in function heads.

I have initially made a wrong assumption. I thought that the Kernel module alone is implicitly imported into each new module. That is only partially correct. The Kernel.SpecialForms module is also implicitly imported, with some important differences:

• You cannot modify or opt out of importing Kernel.SpecialForms, whereas you can modify Kernel imports by making them explicit and passing :only/:except options
• In the AST, usages of Kernel functions can be distinguished from local calls, but usages of Kernel.SpecialForms macros cannot. They look exactly like usages of local function/macros.

I was also confused which module provides which macro, I thought <<>> and :: comes from Kernel, but it coems from Kernel.SpecialForms

TL;DR: we can use assert_call called_fn name: :<<>> to check for calls of special forms with no problems and no modifications necessary. It is not allowed to overwrite those special forms anyway, so you won't have a conflicting local function.

Related PR: exercism/website-copy#2306

[angelikatyborska]

@jiegillet could you review this one?

[jiegillet]

Wonderful, it's nice to see that assert_call was already powerful enough to handle that, thank you for adding the new tests to highlight the behavior.

Sorry that I took so long to review, I still thought that assert_call needed to change, and I was slowly gathering motivation to deep dive back into it, but it seems I never had enough haha. I'm glad you reminded me :)

The code looks great, I just left a suggestion to add a test or two, but it's just a formality.

[jiegillet]

The comment should be triggered if the solution only uses one of the forms right? Should we add tests to check that?

[angelikatyborska]

I added a test with just <<>> but I don't think I can add a test with just ::. It's used for defining binary sizes, so you can't really use it without using the binary special form...

[jiegillet]

GitHub doesn't seem to let me re-run the external tests, I can't find the button, I don't know why.

[angelikatyborska]

I can't find the button, I don't know why.

You can only rerun the tests if the latest test run isn't too old... I think maybe 2 or 4 weeks.

[jiegillet]

Ah that makes sense :)