I have used @compileError for doing validations during compilation, basically to catch errors early on. What’s a good approach to test those validations? Currently I put in the calls that would trigger the @compileError in tests, and test them by doing manual compilation. Then comment them out afterward, with a note left behind saying to uncomment this to test such and such @compileError.
Frankly, I think the test case is when it fails to compile.
While I am confident there are many other use-cases for it beyond validation of types (i.e. anytype that would often cause a complication error down the road anyways) , I mainly use it as a means of providing a helpful error message at the error location instead of some other nebulous compilation error later on with a less helpful message. So instead of a message about a struct not supporting an addition operator in some random function, a consumer gets a message explicitly stating a signed integer or float is required here.
I don’t know if “testing” them really makes a lot of sense within the context of their purpose. i do agree that their could be some cases where it would be helpful, but it is beyond my reasoning how it would even be possible to test such a thing.
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Point taken.
In my case, I’m writing a library and want to make sure the user of the library is using it correctly. Some of the validations are @compileError checks. They become part of the UX of the library. It would be nice to add them to the tests.
It is a accepted proposal.
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Good to know it’s in the pipeline.
You can pull off this kind of testing without any help from the language.
With the Zig build system you can expect a given step to fail and you can capture its stdout/stderr output and compare it against a known good value.
As a similar example, this is how I do snapshot testing with Zine: zine/build.zig at 03734aa552eba662db4d4d166a4220b132b302f9 · kristoff-it/zine · GitHub
In your case you would want to invoke the Zig compiler itself, ask it to build a test project (if the code that you want to test is dependency free, you can even just zig build-exe a single file) and then expect that build to fail in the build system.
Coincidentally, this is also how some Zig compiler tests work.
Related post: Dead Simple Snapshot Testing In Zig | Loris Cro's Blog
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Doing it at the build process would work. Thanks!