trailer: rename *_DEFAULT enums to *_UNSPECIFIED

Do not use *_DEFAULT as a suffix to the enums, because the word
"default" is overloaded. The following are two examples of the ambiguity
of the word "default":

(1) "Default" can mean using the "default" values that are hardcoded
    in trailer.c as

        default_conf_info.where = WHERE_END;
        default_conf_info.if_exists = EXISTS_ADD_IF_DIFFERENT_NEIGHBOR;
        default_conf_info.if_missing = MISSING_ADD;

    in ensure_configured(). These values are referred to as "the
    default" in the docs for interpret-trailers. These defaults are used
    if no "trailer.*" configurations are defined.

(2) "Default" can also mean the "trailer.*" configurations themselves,
    because these configurations are used by "default" (ahead of the
    hardcoded defaults in (1)) if no command line arguments are
    provided.

In addition, the corresponding *_DEFAULT values are chosen when the user
provides the "--no-where", "--no-if-exists", or "--no-if-missing" flags
on the command line. These "--no-*" flags are used to clear previously
provided flags of the form "--where", "--if-exists", and "--if-missing".
Using these "--no-*" flags undoes the specifying of these flags (if
any), so using the word "UNSPECIFIED" is more natural here.

So instead of using "*_DEFAULT", use "*_UNSPECIFIED" because this
signals to the reader that the *_UNSPECIFIED value by itself carries no
meaning (it's a zero value and by itself does not "default" to anything,
necessitating the need to have some other way of getting to a useful
value).

Signed-off-by: Linus Arver <linusa@google.com>

Author: Linus Arver

trailer.c

@@ -388,7 +388,7 @@ static void process_trailers_lists(struct list_head *head,
 int trailer_set_where(enum trailer_where *item, const char *value)
 {
 	if (!value)
-		*item = WHERE_DEFAULT;
+		*item = WHERE_UNSPECIFIED;
 	else if (!strcasecmp("after", value))
 		*item = WHERE_AFTER;
 	else if (!strcasecmp("before", value))
@@ -405,7 +405,7 @@ int trailer_set_where(enum trailer_where *item, const char *value)
 int trailer_set_if_exists(enum trailer_if_exists *item, const char *value)
 {
 	if (!value)
-		*item = EXISTS_DEFAULT;
+		*item = EXISTS_UNSPECIFIED;
 	else if (!strcasecmp("addIfDifferent", value))
 		*item = EXISTS_ADD_IF_DIFFERENT;
 	else if (!strcasecmp("addIfDifferentNeighbor", value))
@@ -424,7 +424,7 @@ int trailer_set_if_exists(enum trailer_if_exists *item, const char *value)
 int trailer_set_if_missing(enum trailer_if_missing *item, const char *value)
 {
 	if (!value)
-		*item = MISSING_DEFAULT;
+		*item = MISSING_UNSPECIFIED;
 	else if (!strcasecmp("doNothing", value))
 		*item = MISSING_DO_NOTHING;
 	else if (!strcasecmp("add", value))
@@ -586,7 +586,10 @@ static void ensure_configured(void)
 	if (configured)
 		return;
 
-	/* Default config must be setup first */
+	/*
+	 * Default config must be setup first. These defaults are used if there
+	 * are no "trailer.*" or "trailer.<token>.*" options configured.
+	 */
 	default_conf_info.where = WHERE_END;
 	default_conf_info.if_exists = EXISTS_ADD_IF_DIFFERENT_NEIGHBOR;
 	default_conf_info.if_missing = MISSING_ADD;
@@ -701,11 +704,11 @@ static void add_arg_item(struct list_head *arg_head, char *tok, char *val,
 	new_item->value = val;
 	duplicate_conf(&new_item->conf, conf);
 	if (new_trailer_item) {
-		if (new_trailer_item->where != WHERE_DEFAULT)
+		if (new_trailer_item->where != WHERE_UNSPECIFIED)
 			new_item->conf.where = new_trailer_item->where;
-		if (new_trailer_item->if_exists != EXISTS_DEFAULT)
+		if (new_trailer_item->if_exists != EXISTS_UNSPECIFIED)
 			new_item->conf.if_exists = new_trailer_item->if_exists;
-		if (new_trailer_item->if_missing != MISSING_DEFAULT)
+		if (new_trailer_item->if_missing != MISSING_UNSPECIFIED)
 			new_item->conf.if_missing = new_trailer_item->if_missing;
 	}
 	list_add_tail(&new_item->list, arg_head);

trailer.h

@@ -5,22 +5,22 @@
 #include "strbuf.h"
 
 enum trailer_where {
-	WHERE_DEFAULT,
+	WHERE_UNSPECIFIED,
 	WHERE_END,
 	WHERE_AFTER,
 	WHERE_BEFORE,
 	WHERE_START
 };
 enum trailer_if_exists {
-	EXISTS_DEFAULT,
+	EXISTS_UNSPECIFIED,
 	EXISTS_ADD_IF_DIFFERENT_NEIGHBOR,
 	EXISTS_ADD_IF_DIFFERENT,
 	EXISTS_ADD,
 	EXISTS_REPLACE,
 	EXISTS_DO_NOTHING
 };
 enum trailer_if_missing {
-	MISSING_DEFAULT,
+	MISSING_UNSPECIFIED,
 	MISSING_ADD,
 	MISSING_DO_NOTHING
 };