build: hide duplicate options from `--help`

Hide --enable variants from [autodetect]'ed options and --enable/--disable
variants for [enable]'d/[disable]'d options. The hidden options are still
usable, just hidden for more readability.

README.md

@@ -27,6 +27,12 @@ you think you have support for some feature installed but configure fails to
 detect it, the file `build/config.log` may contain information about the
 reasons for the failure.
 
+NOTE: To avoid cluttering the output with unreadable spam, `--help` only shows
+one of the two switches for each option. If the option is autodetected by
+default, the `--disable-***` switch is printed; if the option is disabled by
+default, the `--enable-***` switch is printed. Either way, you can use
+`--enable-***` or `--disable-**` regardless of what is printed by `--help`.
+
 To build the software you can use `./waf build`: the result of the compilation
 will be located in `build/mpv`. You can use `./waf install` to install mpv
 to the *prefix* after it is compiled.

waftools/features.py

@@ -1,4 +1,5 @@
 from waflib.Options import OptionsContext
+import optparse
 
 class Feature(object):
     def __init__(self, group, feature):
@@ -43,8 +44,11 @@ class Feature(object):
         return "--{0}-{1}".format(state, self.identifier)
 
     def help(self, state):
+        default = self.behaviour()
+        if (default, state) == ("autodetect", "enable") or default == state:
+            return optparse.SUPPRESS_HELP
         return "{0} {1} [{2}]" \
-            .format(state, self.attributes['desc'], self.behaviour())
+            .format(state, self.attributes['desc'], default)
 
     def storage(self):
         return "enable_{0}".format(self.identifier)