HierarchicalLogging

HierarchicalLogging defines the HierarchicalLogger type, a Base.Logging-compatible logger which can be used to associate a collection of loggers to hierarchically-related objects. E.g., each node N is associated with a .-delimited key

key(N) = key₁.key₂. ... .keyₙ

and a node P is the parent of node C if startswith(label(C), label(P)).

The prototypical example is the module -> submodule relationship in Julia, but you might have your own hierarchically-related objects that you'd like to associate a logger with.

Each node has an associated LogLevel which can be set via min_enabled_level!(logger, key, level), which also recursively sets the level of all children of the node with key. This can be helpful for loggers tied to specific submodules which are particularly noisy.

Example:

using HierarchicalLogging, Logging

module A
    module B
       module C
       end
    end
end
module A1
    module B1
    end
end
module A2 
end
# Logger attached to the root has the lowest possible logging level 
h = HierarchicalLogger(ConsoleLogger(All))
global_logger(h)
insert_logger!(h, A.B, ConsoleLogger(Warn))
insert_logger!(h, A1, ConsoleLogger(Debug))
@info "Hey" _module=A.B.C _file=nothing _line=1
@warn "Uhoh" _module=A.B.C _file=nothing _line=1
# A was never registered to h, so it will use the root logger to log
@debug "In A" _module=A _file=nothing _line=1

Output:

[ Info: Hey
┌ Warning: Uhoh
└ @ Main.A.B.C
┌ Debug: In A
└ @ Main.A

# A wasn't registered before, this will create a copy tied to A with its own log level + set its children to level Error 
min_enabled_level!(h, A, Error)
@warn "This will be ignored" _module=A.B.C _file=nothing _line=1
@error "This won't" _module=A.B _file=nothing _line=1
min_enabled_level!(h, A, Off)
@error "Can't see this" _module=A.B _file=nothing _line=1
@error "This will still show" _module=A2 _file=nothing _line=1

Output:

┌ Error: This won't
└ @ Main.A.B
┌ Error: This will still show
└ @ Main.A2

Inspired by Memento