Add @create_log_macro for making custom styled logging macros

NEWS.md

@@ -116,6 +116,11 @@ Standard library changes
    argument is the output of `bunchkaufman` or `lu` ([#50471]).
 * Structured matrices now retain either the axes of the parent (for `Symmetric`/`Hermitian`/`AbstractTriangular`/`UpperHessenberg`), or that of the principal diagonal (for banded matrices) ([#52480]).
 
+#### Logging
+* New `@create_log_macro` macro for creating new log macros like `@info`, `@warn` etc. For instance
+  `@create_log_macro MyLog 1500 :magenta` will create `@mylog` to be used like `@mylog "hello"` which
+  will show as `┌ MyLog: hello` etc. ([#52196])
+
 #### Printf
 
 #### Profile

base/logging.jl

@@ -162,14 +162,18 @@ const AboveMaxLevel = LogLevel( 1000001)
 # Global log limiting mechanism for super fast but inflexible global log limiting.
 const _min_enabled_level = Ref{LogLevel}(Debug)
 
+# stored as LogLevel => (name, color)
+const custom_log_levels = Dict{LogLevel,Tuple{Symbol,Union{Symbol,Int}}}()
+
 function show(io::IO, level::LogLevel)
-    if     level == BelowMinLevel  print(io, "BelowMinLevel")
-    elseif level == Debug          print(io, "Debug")
-    elseif level == Info           print(io, "Info")
-    elseif level == Warn           print(io, "Warn")
-    elseif level == Error          print(io, "Error")
-    elseif level == AboveMaxLevel  print(io, "AboveMaxLevel")
-    else                           print(io, "LogLevel($(level.level))")
+    if     haskey(custom_log_levels, level) print(io, custom_log_levels[level][1])
+    elseif level == BelowMinLevel           print(io, "BelowMinLevel")
+    elseif level == Debug                   print(io, "Debug")
+    elseif level == Info                    print(io, "Info")
+    elseif level == Warn                    print(io, "Warn")
+    elseif level == Error                   print(io, "Error")
+    elseif level == AboveMaxLevel           print(io, "AboveMaxLevel")
+    else                                    print(io, "LogLevel($(level.level))")
     end
 end
 

stdlib/Logging/docs/src/index.md

@@ -58,7 +58,7 @@ automatically extracted. Let's examine the user-defined data first:
 * The *log level* is a broad category for the message that is used for early
   filtering. There are several standard levels of type [`LogLevel`](@ref);
   user-defined levels are also possible.
-  Each is distinct in purpose:
+  Each built-in log level is distinct in purpose:
   - [`Logging.Debug`](@ref) (log level -1000) is information intended for the developer of
     the program. These events are disabled by default.
   - [`Logging.Info`](@ref) (log level 0) is for general information to the user.
@@ -70,6 +70,17 @@ automatically extracted. Let's examine the user-defined data first:
     Often this log-level is unneeded as throwing an exception can convey
     all the required information.
 
+    You can create logging macros for custom log levels. For instance:
+    ```julia-repl
+    julia> using Logging
+
+    julia> @create_log_macro MyLog 200 :magenta
+    @mylog (macro with 1 method)
+
+    julia> @mylog "hello"
+    [ MyLog: hello
+    ```
+
 * The *message*  is an object describing the event. By convention
   `AbstractString`s passed as messages are assumed to be in markdown format.
   Other types will be displayed using `print(io, obj)` or `string(obj)` for
@@ -298,6 +309,7 @@ Logging.Debug
 Logging.Info
 Logging.Warn
 Logging.Error
+Logging.@create_log_macro
 ```
 
 ### [Processing events with AbstractLogger](@id AbstractLogger-interface)

stdlib/Logging/src/ConsoleLogger.jl

@@ -58,6 +58,7 @@ end
 showvalue(io, ex::Exception) = showerror(io, ex)
 
 function default_logcolor(level::LogLevel)
+    level in keys(custom_log_levels) ? custom_log_levels[level][2] :
     level < Info  ? Base.debug_color() :
     level < Warn  ? Base.info_color()  :
     level < Error ? Base.warn_color()  :

stdlib/Logging/src/Logging.jl

@@ -21,6 +21,7 @@ for sym in [
     Symbol("@warn"),
     Symbol("@error"),
     Symbol("@logmsg"),
+    :custom_log_levels,
     :with_logger,
     :current_logger,
     :global_logger,
@@ -29,6 +30,41 @@ for sym in [
     @eval const $sym = Base.CoreLogging.$sym
 end
 
+"""
+    @create_log_macro(name::Symbol, level::Int, color::Union{Int,Symbol})
+
+Creates a custom log macro like `@info`, `@warn` etc. with a given `name`, `level` and
+`color`. The macro created is named with the lowercase form of `name` but the given form
+is used for the printing.
+
+The available color keys can be seen by typing `Base.text_colors` in the help mode of the REPL
+
+```julia-repl
+julia> @create_log_macro(:MyLog, 200, :magenta)
+@mylog (macro with 1 method)
+
+julia> @mylog "hello"
+[ MyLog: hello
+```
+"""
+macro create_log_macro(name, level, color)
+    macro_name = Symbol(lowercase(string(name)))
+    macro_string = QuoteNode(name)
+    loglevel = LogLevel(level)
+    if loglevel in (BelowMinLevel, Debug, Info, Warn, Error, AboveMaxLevel)
+        throw(ArgumentError("Cannot use the same log level as a built in log macro"))
+    end
+    if haskey(custom_log_levels, loglevel)
+        throw(ArgumentError("Custom log macro already exists for given log level"))
+    end
+    quote
+        $(custom_log_levels)[$(esc(loglevel))] = ($(macro_string), $(esc(color)))
+        macro $(esc(macro_name))(exs...)
+            $(Base.CoreLogging.logmsg_code)(($(Base.CoreLogging.@_sourceinfo))..., $(esc(loglevel)), exs...)
+        end
+    end
+end
+
 # LogLevel aliases (re-)documented here (JuliaLang/julia#40978)
 """
     Debug
@@ -67,6 +103,7 @@ export
     @warn,
     @error,
     @logmsg,
+    @create_log_macro,
     with_logger,
     current_logger,
     global_logger,

stdlib/Logging/test/runtests.jl

@@ -7,8 +7,8 @@ import Logging: min_enabled_level, shouldlog, handle_message
 @noinline func1() = backtrace()
 
 # see "custom log macro" testset
-CustomLog = LogLevel(-500)
-macro customlog(exs...) Base.CoreLogging.logmsg_code((Base.CoreLogging.@_sourceinfo)..., esc(CustomLog), exs...) end
+@create_log_macro CustomLog1 -500 :magenta
+@create_log_macro CustomLog2 1500 1
 
 @testset "Logging" begin
 
@@ -280,16 +280,24 @@ end
 end
 
 @testset "custom log macro" begin
-    @test_logs (CustomLog, "a") min_level=CustomLog @customlog "a"
+    llevel = LogLevel(-500)
+
+    @test_logs (llevel, "foo") min_level=llevel @customlog1 "foo"
 
     buf = IOBuffer()
     io = IOContext(buf, :displaysize=>(30,80), :color=>false)
-    logger = ConsoleLogger(io, CustomLog)
+    logger = ConsoleLogger(io, llevel)
+
+    with_logger(logger) do
+        @customlog1 "foo"
+    end
+    @test occursin("CustomLog1: foo", String(take!(buf)))
+
 
     with_logger(logger) do
-        @customlog "a"
+        @customlog2 "hello"
     end
-    @test occursin("LogLevel(-500): a", String(take!(buf)))
+    @test occursin("CustomLog2: hello", String(take!(buf)))
 end
 
 end