Fix Issue 15771 - FileLogger should create the output directory if it does not exist

Author: RazvanN7

std/experimental/logger/filelogger.d

@@ -21,17 +21,31 @@ class FileLogger : Logger
       file can not be opened for writting an exception will be thrown.
       lv = The $(D LogLevel) for the $(D FileLogger). By default the
       $(D LogLevel) for $(D FileLogger) is $(D LogLevel.all).
+      makeParentDirs = optional boolean value which specifies if the
+      logging system should create the parent directoty structure. It
+      defaults to false.
 
     Example:
     -------------
     auto l1 = new FileLogger("logFile");
     auto l2 = new FileLogger("logFile", LogLevel.fatal);
+    auto l3 = new FileLogger("/home/project/logs/logFile", LogLevel.fatal, true);
     -------------
     */
-    this(in string fn, const LogLevel lv = LogLevel.all) @safe
+    this(in string fn, const LogLevel lv = LogLevel.all, bool makeParentDirs = false) @safe
     {
         super(lv);
         this.filename = fn;
+
+        if (makeParentDirs)
+        {
+            import std.path : dirName;
+            import std.file : exists, mkdirRecurse;
+
+            auto dir = dirName(fn);
+            if (!exists(dir))
+                mkdirRecurse(dir);
+        }
         this.file_.open(this.filename, "a");
     }
 
@@ -158,6 +172,24 @@ class FileLogger : Logger
     assert(readLine.indexOf(notWritten) == -1, readLine);
 }
 
+@system unittest
+{
+    import std.file : rmdirRecurse, exists;
+
+    string filename = "bug15771/minas/oops/bug15771.txt";
+    auto f = new FileLogger(filename, LogLevel.all, true);
+
+    scope(exit)
+    {
+        rmdirRecurse("bug15771");
+    }
+
+    assert(exists("bug15771"));
+    assert(exists("bug15771/minas"));
+    assert(exists("bug15771/minas/oops"));
+    assert(exists(filename));
+}
+
 @system unittest
 {
     import std.array : empty;