Fix documentation and fully cover the function.

std/format/write.d

@@ -502,9 +502,6 @@ The second version of `formattedWrite` takes the format string as a
 template argument. In this case, it is checked for consistency at
 compile-time.
 
-The third version of `formattedWrite` takes the format string as an
-IES, which is converted to a string and passed to the first version.
-
 Params:
  w = an $(REF_ALTTEXT output range, isOutputRange, std, range, primitives),
  where the formatted result is written to
@@ -513,8 +510,6 @@ Params:
  Writer = the type of the writer `w`
  Char = character type of `fmt`
  Args = a variadic list of types of the arguments
- FormatandArgs = the types making up the format IES followed by the types
- of the arguments (used in the third version of the function only).
 
 Returns:
  The index of the last argument that was formatted. If no positional
@@ -701,7 +696,32 @@ if (isSomeString!(typeof(fmt)))
 
 import core.interpolation;
 
+/**
+Converts its arguments according to a format IES and writes
+the result to an output range.
+
+Params:
+ w = an $(REF_ALTTEXT output range, isOutputRange, std, range, primitives),
+ where the formatted result is written to
+ seq = a sequence consisting of the arguments appended to the end of the
+ format IES
+ Writer = the type of the writer `w`
+ FormatandArgs = the types making up the format IES followed by the types
+ of the arguments.
+
+Returns:
+ The index of the last argument that was formatted. If no positional
+ arguments are used, this is the number of arguments that where formatted.
 
+Throws:
+ A $(REF_ALTTEXT FormatException, FormatException, std, format)
+ if formatting did not succeed.
+
+Note:
+ In theory this function should be `@nogc`. But with the current
+ implementation there are some cases where allocations occur.
+ See $(REF_ALTTEXT $(D sformat), sformat, std, format) for more details.
+ */
 uint formattedWrite(Writer, FormatandArgs ...)(auto ref Writer w, FormatandArgs seq) if(is(typeof(seq[0]) == InterpolationHeader))
 {
  string toPass;
@@ -719,8 +739,13 @@ uint formattedWrite(Writer, FormatandArgs ...)(auto ref Writer w, FormatandArgs
  {
  expr = true;
  }
- else static if(is(typeof(e) == InterpolationFooter) && i < seq.length - 2)
- return formattedWrite(w, toPass, seq[i + 2 .. $]);
+ else static if(is(typeof(e) == InterpolationFooter))
+ {
+ if(i < seq.length - 2)
+ return formattedWrite(w, toPass, seq[i + 2 .. $]);
+ else
+ break;
+ }
  else
  {
  if(expr)
@@ -738,7 +763,7 @@ uint formattedWrite(Writer, FormatandArgs ...)(auto ref Writer w, FormatandArgs
  return formattedWrite(w, toPass);
 }
 
-/// Fix Issue 24550
+/// Fix https://issues.dlang.org/show_bug.cgi?id=24550
 @safe pure unittest
 { 
  import std.array : appender;
@@ -749,6 +774,11 @@ uint formattedWrite(Writer, FormatandArgs ...)(auto ref Writer w, FormatandArgs
  formattedWrite(writer, i"$(str1) is the ultimate $(str2).", 42, "answer");
  assert(writer[] == "42 is the ultimate answer.");
 
+ const string w = "World"
+ writer = appender!string();
+ writer.formattedWrite(i"Hello $(w)");
+ assert(writer[] == "Hello World");
+
 }
 
 @safe pure unittest