parse-options.c: make OPTION_COUNTUP respect "unspecified" values

OPT_COUNTUP() merely increments the counter upon --option, and resets it
to 0 upon --no-option, which means that there is no "unspecified" value
with which a client can initialize the counter to determine whether or
not --[no]-option was seen at all.

Make OPT_COUNTUP() treat any negative number as an "unspecified" value
to address this shortcoming. In particular, if a client initializes the
counter to -1, then if it is still -1 after parse_options(), then
neither --option nor --no-option was seen; if it is 0, then --no-option
was seen last, and if it is 1 or greater, than --option was seen last.

This change does not affect the behavior of existing clients because
they all use the initial value of 0 (or more).

Note that builtin/clean.c initializes the variable used with
OPT__FORCE (which uses OPT_COUNTUP()) to a negative value, but it is set
to either 0 or 1 by reading the configuration before the code calls
parse_options(), i.e. as far as parse_options() is concerned, the
initial value of the variable is not negative.

To test this behavior, in test-parse-options.c, "verbose" is set to
"unspecified" while quiet is set to 0 which will test the new behavior
with all sets of values.

Helped-by: Jeff King <peff@peff.net>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Pranit Bauva <pranit.bauva@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/technical/api-parse-options.txt

@@ -144,8 +144,12 @@ There are some macros to easily define options:
 
 `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`.
+	Each use of `--option` increments `int_var`, starting from zero
+	(even if initially negative), and `--no-option` resets it to
+	zero. To determine if `--option` or `--no-option` was encountered at
+	all, initialize `int_var` to a negative value, and if it is still
+	negative after parse_options(), then neither `--option` nor
+	`--no-option` was seen.
 
 `OPT_BIT(short, long, &int_var, description, mask)`::
 	Introduce a boolean option.

parse-options.c

@@ -110,6 +110,8 @@ static int get_value(struct parse_opt_ctx_t *p,
 		return 0;
 
 	case OPTION_COUNTUP:
+		if (*(int *)opt->value < 0)
+			*(int *)opt->value = 0;
 		*(int *)opt->value = unset ? 0 : *(int *)opt->value + 1;
 		return 0;
 

t/t0040-parse-options.sh

@@ -63,7 +63,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -211,7 +211,7 @@ magnitude: 0
 timestamp: 0
 string: 123
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -234,7 +234,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -263,7 +263,7 @@ magnitude: 0
 timestamp: 0
 string: 123
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -302,7 +302,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -322,7 +322,7 @@ magnitude: 0
 timestamp: 1
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 1
 dry run: no
 file: (not set)
@@ -344,7 +344,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -373,7 +373,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -398,7 +398,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -429,7 +429,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -448,7 +448,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -483,7 +483,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 3
 dry run: no
 file: (not set)
@@ -521,7 +521,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)
@@ -540,7 +540,7 @@ magnitude: 0
 timestamp: 0
 string: (not set)
 abbrev: 7
-verbose: 0
+verbose: -1
 quiet: 0
 dry run: no
 file: (not set)

test-parse-options.c

@@ -7,7 +7,8 @@ static int integer = 0;
 static unsigned long magnitude = 0;
 static unsigned long timestamp;
 static int abbrev = 7;
-static int verbose = 0, dry_run = 0, quiet = 0;
+static int verbose = -1; /* unspecified */
+static int dry_run = 0, quiet = 0;
 static char *string = NULL;
 static char *file = NULL;
 static int ambiguous;