Testing for warnings emitted at macro expansion time

General Usage
, ,
1

Hi all,

I’m working on some macros for PikaParser.jl grammars (very WIP!), and I had a question regarding their testing.

One thing I’m trying to do is build the grammar at macro-time; this allows us to return a lambda function applying the parser with rules into the caller, which should allow for precompilable parsers. Because the user may be calling helper functions, this requires an @eval into __module__.

However, this requires symbols to be resolvable at module top-level. If this errors (e.g. because helper functions were defined in a local scope), we recover by issuing a warning about the offending symbol, and defer the grammar build to runtime. That warning is line 74 of this file.

Now, this all works fairly well, and I am writing test-cases. Naively, I expected a @test_warn to work; after some digging, I also tried with @test_logs and by constructing a TestLogger directly.

The fundamental issue is that the @warn invoke happens at macro-time, where stdout/stderr is not captured by the test suite. That test happens here – specifically, at the @syntax macro invoke at line 54.

What are the options here? I would very much like to ensure that this warning is occurring as expected. Should I redirect output streams at macro-expansion time?

Thanks all in advance!

2

For the record, it’s always better to provide permanent links to files or code snippets (and it looks like the line number already change since you posted your message):

3

Ah, yes, probably :slight_smile: I don’t often collaborate with others on code, so my version-control practices are dubious at best!

I’ve just allowed turning off the warning at macro invoke; this solves the issue for me, while letting me test by inspecting the result of @macroexpand.

As it happens, the relevant test line is still at 54:

syntax_exprs = @macroexpand P.@syntax :top begin
    :ws     => many(satisfy(myisspace))
    :number => some(:digit => satisfy(myisdigit))
    :top    => seq(:ws, :number)
end true