# Capturing warnings inside generated functions
**URL:** https://discourse.julialang.org/t/capturing-warnings-inside-generated-functions/132535
**Category:** General Usage
**Tags:** logging, generated
**Created:** [September 21, 2025, 10:21am UTC](https://discourse.julialang.org/t/capturing-warnings-inside-generated-functions/132535 "2025-09-21T10:21:00Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@giordano](https://discourse.julialang.org/u/giordano)
#### Post date: [September 21, 2025, 10:21am UTC](https://discourse.julialang.org/t/capturing-warnings-inside-generated-functions/132535/1 "2025-09-21T10:21:00Z")
Is there a way to capture logging messages (e.g. warnings) issued during compilation, for example from inside a generated function? For example
```julia-auto
julia> using Logging
julia> @generated foo() = @warn "this warning is emitted during compilation"
foo (generic function with 1 method)
julia> with_logger(NullLogger()) do; foo(); end
┌ Warning: this warning is emitted during compilation
└ @ Main REPL[18]:1
```
this doesn’t capture the warning, because it’s emitted before running the body of the `do`-block, during compilation.
Bonus points for a solution which works with `Test.@test_warn`.
---
### Author:  [@Mason](https://discourse.julialang.org/u/Mason)
#### Post date: [September 21, 2025, 11:41am UTC](https://discourse.julialang.org/t/capturing-warnings-inside-generated-functions/132535/2 "2025-09-21T11:41:40Z")
Very hacky workaround, but one approach would be to use `eval` or to store the function in an untyped container:
```julia-auto
julia> using Logging
julia> @generated foo() = @warn "this warning is emitted during compilation";
julia> with_logger(NullLogger()) do
@eval foo()
end
```
```julia-repl
julia> using Logging
julia> @generated foo() = @warn "this warning is emitted during compilation";
julia> let fv = Ref{Any}(foo)
with_logger(NullLogger()) do
fv[]()
end
end
```
Both solutions help ensure that `foo` is not compiled at the same time as the `do` block.
---
### Author:  [@giordano](https://discourse.julialang.org/u/giordano)
#### Post date: [September 21, 2025, 11:56am UTC](https://discourse.julialang.org/t/capturing-warnings-inside-generated-functions/132535/3 "2025-09-21T11:56:56Z")
> [@Mason](#):
>
> one approach would be to use `eval`
Oh, right, `@eval` works also with `@test_warn`:
```julia-auto
julia> @generated foo() = @warn "this warning is emitted during compilation"
foo (generic function with 1 method)
julia> @test_warn "this warning is emitted during compilation" @eval foo()
```
Of course this would fail if the function is called once more:
```julia-auto
julia> @test_warn "this warning is emitted during compilation" @eval foo()
Test Failed at /Users/julia/.julia/scratchspaces/a66863c6-20e8-4ff4-8a62-49f30b1f605e/agent-cache/default-honeycrisp-XG3Q6T6R70.0/build/default-honeycrisp-XG3Q6T6R70-0/julialang/julia-release-1-dot-11/usr/share/julia/stdlib/v1.11/Test/src/Test.jl:896
Expression: contains_warn(read(fname, String), $(Expr(:escape, "this warning is emitted during compilation")))
ERROR: There was an error during testing
```
but inside tests execution is generally deterministic, so that shouldn’t be a problem. Need only to see if using `@eval` in these tests has drawbacks, hopefully not. Thanks!
---
### Author:  [@giordano](https://discourse.julialang.org/u/giordano)
#### Post date: [September 21, 2025, 12:50pm UTC](https://discourse.julialang.org/t/capturing-warnings-inside-generated-functions/132535/4 "2025-09-21T12:50:53Z")
> [@giordano](#):
>
> hopefully not
And of course my hope was ill posed. But wrapping the function in `Ref{Any}` seems to work well, so I think I’ll go with that solution, thanks!
```julia-auto
julia> @testset begin
@generated foo() = @warn "this warning is emitted during compilation"
f = Ref{Any}(foo)
@test_warn "this warning is emitted during compilation" f[]()
end;
Test Summary: | Pass Total Time
test set | 1 1 0.0s
```