New API: ProgressLogging.implementedby(logger)

src/ProgressLogging.jl

@@ -151,6 +151,8 @@ function Logging.handle_message(logger::MyLogger, args...; kwargs...)
     # handle normal log record
 end
 ```
+
+Progress monitors also should define [`implementedby`](@ref).
 """
 asprogress(_level, progress::Progress, _args...; _...) = progress
 function asprogress(
@@ -506,4 +508,20 @@ function make_count_to_frac(iterators...)
     return count_to_frac
 end
 
+"""
+    ProgressLogging.implementedby(logger::AbstractLogger) :: Bool
+
+Check if ProgressLogging protocol is supported by `logger`.
+
+# Implementation
+
+A progress monitor `CustomLogger <: AbstractLogger` should define
+
+```julia
+ProgressLogging.implementedby(::CustomLogger) = true
+```
+"""
+implementedby
+implementedby(@nospecialize(logger::Logging.AbstractLogger)) = false
+
 end # module

test/test_misc.jl

@@ -0,0 +1,11 @@
+module TestMisc
+
+using ProgressLogging
+using Test
+using Logging
+
+@testset "implementedby" begin
+    @test ProgressLogging.implementedby(NullLogger()) == false
+end
+
+end  # module