[logger] Allow report callback with two arguments returning a string

If the report callback is a fun of arity 2, then the second argument
is a map with the keys 'encoding', 'depth' and 'chars_limit', and the
fun must return a string which is size limited according to the given
depth and chars_limit.

If the report callback is a fun of arity 1, then it must return a
tuple containing a format string and a list of arguments. The
formatter will produce the string, and limit it's size.

3 files changed, 46 insertions, 6 deletions

diff --git a/lib/kernel/doc/src/logger.xml b/lib/kernel/doc/src/logger.xml
index 8bf62a6b39..f1830a8224 100644
--- a/lib/kernel/doc/src/logger.xml
+++ b/lib/kernel/doc/src/logger.xml
@@ -227,7 +227,10 @@ logger:error("error happened because: ~p", [Reason]). % Without macro
 	      a <seealso marker="#type-report"><c>report()</c></seealso>,
 	      the <c>report_cb</c> key can be associated with a fun
 	      (report callback) that converts the report to a format
-	      string and arguments. See
+	      string and arguments, or directly to a string. See the
+	      type definition
+	      of <seealso marker="#type-report_cb"><c>report_cb()</c></seealso>,
+	      and
 	      section <seealso marker="logger_chapter#log_message">Log
 	      Message</seealso> in the User's Guide for more
 	      information about report callbacks.</p>
@@ -260,6 +263,22 @@ logger:error("error happened because: ~p", [Reason]). % Without macro
       </desc>
     </datatype>
     <datatype>
+      <name name="report_cb"/>
+      <desc>
+	<p>A fun which converts a <seealso marker="#type-report"><c>report()</c>
+	  </seealso> to a format string and arguments, or directly to a string.
+	  See section <seealso marker="logger_chapter#log_message">Log
+	    Message</seealso> in the User's Guide for more
+	  information.</p>
+      </desc>
+    </datatype>
+    <datatype>
+      <name name="report_cb_config"/>
+      <desc>
+	<p></p>
+      </desc>
+    </datatype>
+    <datatype>
       <name name="timestamp"/>
       <desc>
 	<p>A timestamp produced
diff --git a/lib/kernel/doc/src/logger_chapter.xml b/lib/kernel/doc/src/logger_chapter.xml
index 23a289f2ee..dc68d5c761 100644
--- a/lib/kernel/doc/src/logger_chapter.xml
+++ b/lib/kernel/doc/src/logger_chapter.xml
@@ -194,10 +194,26 @@
 	the log event's <seealso marker="#metadata">metadata</seealso>.
 	The report callback is a convenience function that
 	the <seealso marker="#formatters">formatter</seealso> can use
-	to convert the report to a format string and arguments. The
+	to convert the report to a format string and arguments, or
+	directly to a string. The
 	formatter can also use its own conversion function, if no
 	callback is provided, or if a customized formatting is
 	desired.</p>
+      <p>The report callback must be a fun with one or two
+	arguments. If it takes one argument, this is the report
+	itself, and the fun returns a format string and arguments:</p>
+      <pre>fun((<seealso marker="logger#type-report"><c>logger:report()</c></seealso>) -> {<seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso>,[term()]})</pre>
+      <p>If it takes two arguments, the first is the report, and the
+	second is a map containing extra data that allows direct
+	coversion to a string:</p>
+      <pre>fun((<seealso marker="logger#type-report"><c>logger:report()</c></seealso>,<seealso marker="logger#type-report_cb_config"><c>logger:report_cb_config()</c></seealso>) -> <seealso marker="stdlib:unicode#type-chardata"><c>unicode:chardata()</c></seealso>)
+      </pre>
+      <p>The fun must obey the <c>encoding</c>, <c>depth</c>
+	and <c>chars_limit</c> parameters provided in the second
+	argument, as the formatter can not do anything useful of these
+	parameters with the returned string. This variant is used when
+	the formatting of the report depends on the size and encoding
+	parameters.</p>
       <p>Example, format string and arguments:</p>
       <code>logger:error("The file does not exist: ~ts",[Filename])</code>
       <p>Example, string:</p>
diff --git a/lib/kernel/doc/src/logger_formatter.xml b/lib/kernel/doc/src/logger_formatter.xml
index a482d02293..9226d19834 100644
--- a/lib/kernel/doc/src/logger_formatter.xml
+++ b/lib/kernel/doc/src/logger_formatter.xml
@@ -82,6 +82,13 @@
 	      in STDLIB.</p>
 	    <p>Defaults to <c>unlimited</c>.</p>
 	  </item>
+	  <tag><c>encoding = </c><seealso marker="stdlib:unicode#type-encoding">
+	      <c>unicode:encoding()</c></seealso></tag>
+	  <item>
+	    <p>This parameter must reflect the encoding of the device
+	      that the handler prints to.</p>
+	    <p>Defaults to <c>utf8</c></p>
+	  </item>
 	  <tag><c>legacy_header = boolean()</c></tag>
 	  <item>
 	    <p>If set to <c>true</c> a header field is added to
@@ -105,7 +112,8 @@
 	      by <c>chars_limit</c> or <c>depth</c>, it is truncated.</p>
 	    <p>Defaults to <c>unlimited</c>.</p>
 	  </item>
-	  <tag><c>report_cb = fun((</c><seealso marker="logger#type-report"><c>logger:report()</c></seealso><c>) -> {</c><seealso marker="stdlib:io#type-format"><c>io:format()</c></seealso><c>, [term()]})</c></tag>
+	  <tag><c>report_cb = </c><seealso marker="logger#type-report_cb">
+	      <c>logger:report_cb()</c></seealso></tag>
 	  <item>
 	    <p>A report callback is used by the formatter to transform
 	      log messages on report form to a format string and
@@ -119,9 +127,6 @@
 	      both the default report callback, and any report
 	      callback found in metadata. That is, all reports are
 	      converted by this configured function.</p>
-	    <p>The value must be a function with arity 1,
-	      returning <c>{Format,Args}</c>, and it will be called
-	      with a report as only argument.</p>
 	  </item>
 	  <tag><c>single_line = boolean()</c></tag>
 	  <item>