devtool: add a 'latest-version' command

index f6141bfdc38..445e0642460 100644
@@ -498,6 +498,26 @@ def upgrade(args, config, basepath, workspace):
         tinfoil.shutdown()
     return 0
 
+def latest_version(args, config, basepath, workspace):
+    """Entry point for the devtool 'latest_version' subcommand"""
+    tinfoil = setup_tinfoil(basepath=basepath, tracking=True)
+    try:
+        rd = parse_recipe(config, tinfoil, args.recipename, True)
+        if not rd:
+            return 1
+        version_info = oe.recipeutils.get_recipe_upstream_version(rd)
+        # "new-commits-available" is an indication that upstream never issues version tags
+        if not version_info['version'].endswith("new-commits-available"):
+            logger.info("Current version: {}".format(version_info['current_version']))
+            logger.info("Latest version: {}".format(version_info['version']))
+            if version_info['revision']:
+                logger.info("Latest version's commit: {}".format(version_info['revision']))
+        else:
+            logger.info("Latest commit: {}".format(version_info['revision']))
+    finally:
+        tinfoil.shutdown()
+    return 0
+
 def register_commands(subparsers, context):
     """Register devtool subcommands from this plugin"""
 

@@ -519,3 +539,9 @@ def register_commands(subparsers, context):
     group.add_argument('--no-same-dir', help='Force build in a separate build directory', action="store_true")
     parser_upgrade.add_argument('--keep-temp', action="store_true", help='Keep temporary directory (for debugging)')
     parser_upgrade.set_defaults(func=upgrade, fixed_setup=context.fixed_setup)
+
+    parser_latest_version = subparsers.add_parser('latest-version', help='Report the latest version of an existing recipe',
+                                                  description='Queries the upstream server for what the latest upstream release is (for git, tags are checked, for tarballs, a list of them is obtained, and one with the highest version number is reported)',
+                                                  group='info')
+    parser_latest_version.add_argument('recipename', help='Name of recipe to query (just name - no version, path or extension)')
+    parser_latest_version.set_defaults(func=latest_version)

index 445e0642460..28fbdaee357 100644
@@ -433,8 +433,6 @@ def upgrade(args, config, basepath, workspace):
 
     if args.recipename in workspace:
         raise DevtoolError("recipe %s is already in your workspace" % args.recipename)
-    if not args.version and not args.srcrev:
-        raise DevtoolError("You must provide a version using the --version/-V option, or for recipes that fetch from an SCM such as git, the --srcrev/-S option")
     if args.srcbranch and not args.srcrev:
         raise DevtoolError("If you specify --srcbranch/-B then you must use --srcrev/-S to specify the revision" % args.recipename)
 

@@ -457,6 +455,16 @@ def upgrade(args, config, basepath, workspace):
         else:
             srctree = standard.get_default_srctree(config, pn)
 
+        # try to automatically discover latest version and revision if not provided on command line
+        if not args.version and not args.srcrev:
+            version_info = oe.recipeutils.get_recipe_upstream_version(rd)
+            if version_info['version'] and not version_info['version'].endswith("new-commits-available"):
+                args.version = version_info['version']
+            if version_info['revision']:
+                args.srcrev = version_info['revision']
+        if not args.version and not args.srcrev:
+            raise DevtoolError("Automatic discovery of latest version/revision failed - you must provide a version using the --version/-V option, or for recipes that fetch from an SCM such as git, the --srcrev/-S option.")
+
         standard._check_compatible_recipe(pn, rd)
         old_srcrev = rd.getVar('SRCREV')
         if old_srcrev == 'INVALID':

@@ -528,8 +536,8 @@ def register_commands(subparsers, context):
                                            group='starting')
     parser_upgrade.add_argument('recipename', help='Name of recipe to upgrade (just name - no version, path or extension)')
     parser_upgrade.add_argument('srctree',  nargs='?', help='Path to where to extract the source tree. If not specified, a subdirectory of %s will be used.' % defsrctree)
-    parser_upgrade.add_argument('--version', '-V', help='Version to upgrade to (PV)')
-    parser_upgrade.add_argument('--srcrev', '-S', help='Source revision to upgrade to (required if fetching from an SCM such as git)')
+    parser_upgrade.add_argument('--version', '-V', help='Version to upgrade to (PV). If omitted, latest upstream version will be determined and used, if possible.')
+    parser_upgrade.add_argument('--srcrev', '-S', help='Source revision to upgrade to (useful when fetching from an SCM such as git)')
     parser_upgrade.add_argument('--srcbranch', '-B', help='Branch in source repository containing the revision to use (if fetching from an SCM such as git)')
     parser_upgrade.add_argument('--branch', '-b', default="devtool", help='Name for new development branch to checkout (default "%(default)s")')
     parser_upgrade.add_argument('--no-patch', action="store_true", help='Do not apply patches from the recipe to the new source code')