Allow to print dump of SCons environment using "envdump" target

platformio/builder/tools/platformio.py

@@ -6,7 +6,8 @@ import re
 from os import getenv, listdir, remove, sep, walk
 from os.path import basename, dirname, isdir, isfile, join, normpath
 
-from SCons.Script import Exit, SConscript, SConscriptChdir
+from SCons.Script import (COMMAND_LINE_TARGETS, Exit, SConscript,
+                          SConscriptChdir)
 from SCons.Util import case_sensitive_suffixes
 
 from platformio.util import pioversion_to_intstr
@@ -60,6 +61,10 @@ def BuildFirmware(env):
             *pioversion_to_intstr())]
     )
 
+    if "envdump" in COMMAND_LINE_TARGETS:
+        print env.Dump()
+        Exit()
+
     return firmenv.Program(
         join("$BUILD_DIR", "firmware"),
         [firmenv.GlobCXXFiles(vdir) for vdir in vdirs],