parse-options: deprecate OPT_BOOLEAN

It is natural to expect that an option defined with OPT_BOOLEAN() could be
used in this way:

	int option = -1; /* unspecified */

	struct option options[] = {
		OPT_BOOLEAN(0, "option", &option, "set option"),
                OPT_END()
	};
	parse_options(ac, av, prefix, options, usage, 0);

        if (option < 0)
        	... do the default thing ...
	else if (!option)
		... --no-option was given ...
	else
		... --option was given ...

to easily tell three cases apart:

 - There is no mention of the `--option` on the command line;
 - The variable is positively set with `--option`; or
 - The variable is explicitly negated with `--no-option`.

Unfortunately, this is not the case. OPT_BOOLEAN() increments the variable
every time `--option` is given, and resets it to zero when `--no-option`
is given.

As a first step to remedy this, introduce a true boolean OPT_BOOL(), and
rename OPT_BOOLEAN() to OPT_COUNTUP(). To help transitioning, OPT_BOOLEAN
and OPTION_BOOLEAN are defined as deprecated synonyms to OPT_COUNTUP and
OPTION_COUNTUP respectively.

This is what db7244b (parse-options new features., 2007-11-07) from four
years ago started by marking OPTION_BOOLEAN as "INCR would have been a
better name".

Some existing users do depend on the count-up semantics; for example,
users of OPT__VERBOSE() could use it to raise the verbosity level with
repeated use of `-v` on the command line, but they probably should be
rewritten to use OPT__VERBOSITY() instead these days.  I suspect that some
users of OPT__FORCE() may also use it to implement different level of
forcibleness but I didn't check.

On top of this patch, here are the remaining clean-up tasks that other
people can help:

 - Look at each hit in "git grep -e OPT_BOOLEAN"; trace all uses of the
   value that is set to the underlying variable, and if it can proven that
   the variable is only used as a boolean, replace it with OPT_BOOL(). If
   the caller does depend on the count-up semantics, replace it with
   OPT_COUNTUP() instead.

 - Same for OPTION_BOOLEAN; replace it with OPTION_SET_INT and arrange to
   set 1 to the variable for a true boolean, and otherwise replace it with
   OPTION_COUNTUP.

 - Look at each hit in "git grep -e OPT__VERBOSE -e OPT__QUIET" and see if
   they can be replaced with OPT__VERBOSITY().

I'll follow this message up with a separate patch as an example.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 5 deletions

diff --git a/Documentation/technical/api-parse-options.txt b/Documentation/technical/api-parse-options.txt
index f6a4a361b..acf17607d 100644
--- a/Documentation/technical/api-parse-options.txt
+++ b/Documentation/technical/api-parse-options.txt
@@ -135,9 +135,14 @@ There are some macros to easily define options:
 	describes the group or an empty string.
 	Start the description with an upper-case letter.
 
-`OPT_BOOLEAN(short, long, &int_var, description)`::
-	Introduce a boolean option.
-	`int_var` is incremented on each use.
+`OPT_BOOL(short, long, &int_var, description)`::
+	Introduce a boolean option. `int_var` is set to one with
+	`--option` and set to zero with `--no-option`.
+
+`OPT_COUNTUP(short, long, &int_var, description)`::
+	Introduce a count-up option.
+	`int_var` is incremented on each use of `--option`, and
+	reset to zero with `--no-option`.
 
 `OPT_BIT(short, long, &int_var, description, mask)`::
 	Introduce a boolean option.
@@ -148,8 +153,9 @@ There are some macros to easily define options:
 	If used, `int_var` is bitwise-anded with the inverted `mask`.
 
 `OPT_SET_INT(short, long, &int_var, description, integer)`::
-	Introduce a boolean option.
-	If used, set `int_var` to `integer`.
+	Introduce an integer option.
+	`int_var` is set to `integer` with `--option`, and
+	reset to zero with `--no-option`.
 
 `OPT_SET_PTR(short, long, &ptr_var, description, ptr)`::
 	Introduce a boolean option.