Merge mozilla-central and inbound

python/mozbuild/mozbuild/mach_commands.py

@@ -294,6 +294,17 @@ class Build(MachCommandBase):
                     if make_dir is None and make_target is None:
                         return 1
 
+                    # See bug 886162 - we don't want to "accidentally" build
+                    # the entire tree (if that's really the intent, it's
+                    # unlikely they would have specified a directory.)
+                    if not make_dir and not make_target:
+                        print("The specified directory doesn't contain a "
+                              "Makefile and the first parent with one is the "
+                              "root of the tree. Please specify a directory "
+                              "with a Makefile or run |mach build| if you "
+                              "want to build the entire tree.")
+                        return 1
+
                     target_pairs.append((make_dir, make_target))
 
                 # Possibly add extra make depencies using dumbmake.