Improved formatting defaults for log metadata

The metadata suffix is now printed on its own line by default, and
disabled for `Info` level logging.  The printing can be made more
compact if desired by right justifying the metadata using the
`right_justify` setting.

Color is made customizable by requiring that it's returned from the
meta_formatter() function.

stdlib/Logging/src/ConsoleLogger.jl

@@ -1,7 +1,8 @@
 # This file is a part of Julia. License is MIT: https://julialang.org/license
 
 """
-    ConsoleLogger(stream=STDERR, min_level=Info; meta_formatter=default_metafmt, show_limited=true)
+    ConsoleLogger(stream=STDERR, min_level=Info; meta_formatter=default_metafmt,
+                  show_limited=true, right_justify=0)
 
 Logger with formatting optimized for readability in a text console, for example
 interactive work with the Julia REPL.
@@ -11,24 +12,29 @@ Log levels less than `min_level` are filtered out.
 Message formatting can be controlled by setting keyword arguments:
 
 * `meta_formatter` is a function which takes the log event metadata
-  `(level, _module, group, id, file, line)` and produces a prefix and suffix
-  for the log message.  The default is to prefix with the log level and add a
-  suffix containing the module, file and line location.
+  `(level, _module, group, id, file, line)` and returns a color (as would be
+  passed to print_with_color), prefix and suffix for the log message.  The
+  default is to prefix with the log level and a suffix containing the module,
+  file and line location.
 * `show_limited` limits the printing of large data structures to something
   which can fit on the screen by setting the `:limit` `IOContext` key during
   formatting.
+* `right_justify` is the integer column which log metadata is right justified
+  at. The default is zero (metadata goes on its own line).
 """
 struct ConsoleLogger <: AbstractLogger
     stream::IO
     min_level::LogLevel
     meta_formatter
     show_limited::Bool
+    right_justify::Int
     message_limits::Dict{Any,Int}
 end
 function ConsoleLogger(stream::IO=STDERR, min_level=Info;
-                       meta_formatter=default_metafmt, show_limited=true)
+                       meta_formatter=default_metafmt, show_limited=true,
+                       right_justify=0)
     ConsoleLogger(stream, min_level, meta_formatter,
-                  show_limited, Dict{Any,Int}())
+                  show_limited, right_justify, Dict{Any,Int}())
 end
 
 shouldlog(logger::ConsoleLogger, level, _module, group, id) =
@@ -44,9 +50,39 @@ function showvalue(io, e::Tuple{Exception,Any})
 end
 showvalue(io, ex::Exception) = showvalue(io, (ex,catch_backtrace()))
 
+function default_logcolor(level)
+    level < Info  ? Base.debug_color() :
+    level < Warn  ? Base.info_color()  :
+    level < Error ? Base.warn_color()  :
+                    Base.error_color()
+end
+
 function default_metafmt(level, _module, group, id, file, line)
-    ((level == Warn ? "Warning" : string(level))*':',
-     "@ $_module $(basename(file)):$line")
+    color = default_logcolor(level)
+    prefix = (level == Warn ? "Warning" : string(level))*':'
+    suffix = (Info <= level < Warn) ? "" : "@ $_module $(basename(file)):$line"
+    color,prefix,suffix
+end
+
+# Length of a string as it will appear in the terminal (after ANSI color codes
+# are removed)
+function termlength(str)
+    N = 0
+    in_esc = false
+    for c in str
+        if in_esc
+            if c == 'm'
+                in_esc = false
+            end
+        else
+            if c == '\e'
+                in_esc = true
+            else
+                N += 1
+            end
+        end
+    end
+    return N
 end
 
 function handle_message(logger::ConsoleLogger, level, message, _module, group, id,
@@ -56,63 +92,64 @@ function handle_message(logger::ConsoleLogger, level, message, _module, group, i
         logger.message_limits[id] = remaining - 1
         remaining > 0 || return
     end
-    color = level < Info  ? Base.debug_color() :
-            level < Warn  ? Base.info_color() :
-            level < Error ? Base.warn_color() :
-                            Base.error_color()
-    buf = IOBuffer()
-    iob = IOContext(buf, logger.stream)
-    if logger.show_limited
-        iob = IOContext(iob, :limit=>true)
-    end
-    msglines = split(chomp(string(message)), '\n')
+
+    # Generate a text representation of the message and all key value pairs,
+    # split into lines.
+    msglines = [(indent=0,msg=l) for l in split(chomp(string(message)), '\n')]
     dsize = displaysize(logger.stream)
-    width = dsize[2]
-    prefix,suffix = logger.meta_formatter(level, _module, group, id, filepath, line)
-    length(prefix) == 0 || (prefix = prefix*" ")
-    length(suffix) == 0 || (suffix = " "*suffix)
-    singlelinewidth = 2 + length(msglines[1]) + length(prefix) + length(suffix)
-    issingleline = length(msglines) + length(kwargs) == 1 && singlelinewidth <= width
-    print_with_color(color, iob, issingleline ? "[ " : "┌ ", bold=true)
-    if length(prefix) > 0
-        print_with_color(color, iob, prefix, bold=true)
-    end
-    print(iob, msglines[1])
-    if issingleline
-        npad = (width - singlelinewidth)
-    else
-        println(iob)
-        for i in 2:length(msglines)
-            print_with_color(color, iob, "│ ", bold=true)
-            println(iob, msglines[i])
-        end
+    if !isempty(kwargs)
         valbuf = IOBuffer()
         rows_per_value = max(1, dsize[1]÷(length(kwargs)+1))
-        valio = IOContext(IOContext(valbuf, iob),
+        valio = IOContext(IOContext(valbuf, logger.stream),
                           :displaysize=>(rows_per_value,dsize[2]-5))
+        if logger.show_limited
+            valio = IOContext(valio, :limit=>true)
+        end
         for (key,val) in pairs(kwargs)
-            print_with_color(color, iob, "│ ", bold=true)
-            print(iob, "  ", key, " =")
             showvalue(valio, val)
             vallines = split(String(take!(valbuf)), '\n')
             if length(vallines) == 1
-                println(iob, " ", vallines[1])
+                push!(msglines, (indent=2,msg=SubString("$key = $(vallines[1])")))
             else
-                println(iob)
-                for line in vallines
-                    print_with_color(color, iob, "│    ", bold=true)
-                    println(iob, line)
-                end
+                push!(msglines, (indent=2,msg=SubString("$key =")))
+                append!(msglines, ((indent=3,msg=line) for line in vallines))
             end
         end
-        print_with_color(color, iob, "└ ", bold=true)
-        npad = width - 2 - length(suffix)
     end
-    if length(suffix) > 0
-        print(iob, " "^npad)
-        print_with_color(:light_black, iob, suffix, bold=false)
+
+    # Format lines as text with appropriate indentation and with a box
+    # decoration on the left.
+    color,prefix,suffix = logger.meta_formatter(level, _module, group, id, filepath, line)
+    minsuffixpad = 2
+    buf = IOBuffer()
+    iob = IOContext(buf, logger.stream)
+    nonpadwidth = 2 + (isempty(prefix) || length(msglines) > 1 ? 0 : length(prefix)+1) +
+                  msglines[end].indent + termlength(msglines[end].msg) +
+                  (isempty(suffix) ? 0 : length(suffix)+minsuffixpad)
+	justify_width = min(logger.right_justify, dsize[2])
+    if nonpadwidth > justify_width && !isempty(suffix)
+        push!(msglines, (indent=0,msg=SubString("")))
+        minsuffixpad = 0
+        nonpadwidth = 2 + length(suffix)
+    end
+    for (i,(indent,msg)) in enumerate(msglines)
+        boxstr = length(msglines) == 1 ? "[ " :
+                 i == 1                ? "┌ " :
+                 i < length(msglines)  ? "│ " :
+                                         "└ "
+        print_with_color(color, iob, boxstr, bold=true)
+        if i == 1 && !isempty(prefix)
+            print_with_color(color, iob, prefix, " ", bold=true)
+        end
+        print(iob, " "^indent, msg)
+        if i == length(msglines) && !isempty(suffix)
+            npad = max(0, justify_width - nonpadwidth) + minsuffixpad
+            print(iob, " "^npad)
+            print_with_color(:light_black, iob, suffix)
+        end
+        println(iob)
     end
-    print(iob, "\n")
+
     write(logger.stream, take!(buf))
     nothing
 end