add special handling for exceptions in JSON format

Project.toml

@@ -1,6 +1,6 @@
 name = "LoggingFormats"
 uuid = "98105f81-4425-4516-93fd-1664fb551ab6"
-version = "1.1.0"
+version = "1.2.0"
 
 [deps]
 JSON3 = "0f8b85d8-7281-11e9-16c2-39a750bddbf1"

README.md

@@ -37,7 +37,18 @@ julia> with_logger(FormatLogger(LoggingFormats.JSON(; recursive=true), stderr))
 ```
 
 If it encounters something which does not have a defined `StructTypes.StructType` to use
-for serializing to JSON, it will fallback to converting the objects to strings, like the default `recursive=false` option does.
+for serializing to JSON, it will fallback to converting the objects to strings, like the default `recursive=false` option does. Handles the key `exception` specially, by printing errors and stacktraces using `Base.showerror`.
+
+```julia
+julia> f() = try
+                throw(ArgumentError("Bad input"))
+            catch e
+                @error "Input error" exception=(e, catch_backtrace())
+            end
+
+julia> with_logger(f, FormatLogger(LoggingFormats.JSON(; recursive=true), stderr))
+{"level":"error","msg":"Input error","module":"Main","file":"REPL[2]","line":4,"group":"REPL[2]","id":"Main_a226875f","kwargs":{"exception":"ERROR: ArgumentError: Bad input\nStacktrace:\n [1] f()\n   @ Main ./REPL[2]:2\n [2] with_logstate(f::Function, logstate::Any)\n   @ Base.CoreLogging ./logging.jl:511\n [3] with_logger(f::Function, logger::FormatLogger)\n   @ Base.CoreLogging ./logging.jl:623\n [4] top-level scope\n   @ REPL[3]:1\n"}}
+```
 
 ## `LogFmt`: Format log events as logfmt
 

src/LoggingFormats.jl

@@ -70,6 +70,17 @@ end
 transform(::Type{String}, v) = string(v)
 transform(::Type{Any}, v) = v
 
+# Use key information, then lower to 2-arg transform
+function transform(::Type{T}, key, v) where {T}
+    key == :exception || return transform(T, v)
+    if v isa Tuple && length(v) == 2 && v[1] isa Exception
+        e, bt = v
+        msg = sprint(Base.display_error, e, bt)
+        return transform(T, msg)
+    end
+    return transform(T, sprint(showerror, v))
+end
+
 function JSONLogMessage{T}(args) where {T}
     JSONLogMessage{T}(
         lvlstr(args.level),
@@ -79,7 +90,7 @@ function JSONLogMessage{T}(args) where {T}
         args.line,
         args.group === nothing ? nothing : string(args.group),
         args.id === nothing ? nothing : string(args.id),
-        Dict{String,T}(string(k) => transform(T, v) for (k, v) in args.kwargs)
+        Dict{String,T}(string(k) => transform(T, k, v) for (k, v) in args.kwargs)
     )
 end
 StructTypes.StructType(::Type{<:JSONLogMessage}) = StructTypes.OrderedStruct()
@@ -98,7 +109,7 @@ function (j::JSON)(io, args)
             JSON3.write(io, logmsg)
         catch e
             fallback_msg = JSONLogMessage{String}(args)
-            fallback_msg.kwargs["LoggingFormats.FormatError"] = sprint(Base.showerror, e)
+            fallback_msg.kwargs["LoggingFormats.FormatError"] = sprint(showerror, e)
             JSON3.write(io, fallback_msg)
         end
     else

test/runtests.jl

@@ -113,12 +113,12 @@ end
     @test json.kwargs.y == Dict(:hi => Dict(:hi2 => [1,2]))
 
     # Fallback to strings
-     io = IOBuffer()
-     with_logger(FormatLogger(JSON(; recursive=true), io)) do
-         y = (1, 2)
-         @info "info msg" x = [1, 2, 3] y = Dict("hi" => NoStructTypeDefined(1))
-     end
-     json = JSON3.read(seekstart(io))
+    io = IOBuffer()
+    with_logger(FormatLogger(JSON(; recursive=true), io)) do
+        y = (1, 2)
+        @info "info msg" x = [1, 2, 3] y = Dict("hi" => NoStructTypeDefined(1))
+    end
+    json = JSON3.read(seekstart(io))
     @test json.level == "info"
     @test json.msg == "info msg"
     @test json.module == "Main"
@@ -129,6 +129,38 @@ end
     @test all(h -> occursin(h, y), must_have) # avoid issues with printing changing with versions
     @test json.kwargs[Symbol("LoggingFormats.FormatError")] == "ArgumentError: NoStructTypeDefined doesn't have a defined `StructTypes.StructType`"
 
+    # Test logging exceptions
+    for recursive in (false, true)
+        # no stacktrace
+        io = IOBuffer()
+        with_logger(FormatLogger(JSON(; recursive=recursive), io)) do
+            try
+                throw(ArgumentError("no"))
+            catch e
+                @error "Oh no" exception = e
+            end
+        end
+        logs = JSON3.read(seekstart(io))
+        @test logs["msg"] == "Oh no"
+        @test logs["kwargs"]["exception"] == "ArgumentError: no"
+
+        # stacktrace
+        io = IOBuffer()
+        with_logger(FormatLogger(JSON(; recursive=recursive), io)) do
+            try
+                throw(ArgumentError("no"))
+            catch e
+                @error "Oh no" exception = (e, catch_backtrace())
+            end
+        end
+        logs = JSON3.read(seekstart(io))
+        @test logs["msg"] == "Oh no"
+
+        @test occursin("ArgumentError: no", logs["kwargs"]["exception"])
+        # Make sure we get a stacktrace out:
+        @test occursin(r"ArgumentError: no\nStacktrace:\s* \[1\]",
+                    logs["kwargs"]["exception"])
+    end
 end
 
 @testset "logfmt" begin