Getting PyCall tests to work with Julia 1.7 / Core.TypeofVararg

Last night I waged war with PyCall.jl’s tests. Today I have a minimal PR to fix them. I’m writing up the story in case anyone encounters similar issues with Core.TypeofVararg or AOT compilation tests.

PyCall’s tests were failing on Julia nightly since the type of Vararg changed to Core.TypeofVararg in Julia nightly (1.7) since there was no method pyany_toany(::Core.TypeofVararg).

MethodError: no method matching pyany_toany(::Core.TypeofVararg)

Core.TypeofVararg was introduced in #38136, version v"1.7.0-DEV.77", with commit 80ace52b. Thanks to @ararslan and @simeonschaub for teaching me how to use contrib/ to find this information.

While I thought I had fixed this by adding an if statement to add the appropriate method to PyCall, the AOT tests were still stubbornly failing.

Eventually I figured out that the AOT tests were actually testing master rather than my changes in my pull request since there was a call to pkg"dev PyCall" just before running the tests and the environment had not been changed. It turns out a command line option for --project was missing, and Julia was having trouble finding the version of PyCall cloned a few steps earlier.

Ultimately, I was able to resolve all the issues in few lines of a compact commit.

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According to JuliaLang/julia#39239 (comment), Core.TypeofVararg should be spelled typeof(Vararg).