ref-filter: implement %(if:equals=<string>) and %(if:notequals=<string>)

Implement %(if:equals=<string>) wherein the if condition is only
satisfied if the value obtained between the %(if:...) and %(then) atom
is the same as the given '<string>'.

Similarly, implement (if:notequals=<string>) wherein the if condition
is only satisfied if the value obtained between the %(if:...) and
%(then) atom is different from the given '<string>'.

This is done by introducing 'if_atom_parser()' which parses the given
%(if) atom and then stores the data in used_atom which is later passed
on to the used_atom of the %(then) atom, so that it can do the required
comparisons.

Add tests and documentation for the same.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 41 insertions, 5 deletions

diff --git a/ref-filter.c b/ref-filter.c
index f31c4b68b..302bb2d06 100644
--- a/ref-filter.c
+++ b/ref-filter.c
@@ -16,6 +16,7 @@
 #include "trailer.h"
 
 typedef enum { FIELD_STR, FIELD_ULONG, FIELD_TIME } cmp_type;
+typedef enum { COMPARE_EQUAL, COMPARE_UNEQUAL, COMPARE_NONE } cmp_status;
 
 struct align {
 	align_type position;
@@ -23,6 +24,8 @@ struct align {
 };
 
 struct if_then_else {
+	cmp_status cmp_status;
+	const char *str;
 	unsigned int then_atom_seen : 1,
 		else_atom_seen : 1,
 		condition_satisfied : 1;
@@ -50,6 +53,10 @@ static struct used_atom {
 			enum { C_BARE, C_BODY, C_BODY_DEP, C_LINES, C_SIG, C_SUB, C_TRAILERS } option;
 			unsigned int nlines;
 		} contents;
+		struct {
+			cmp_status cmp_status;
+			const char *str;
+		} if_then_else;
 		enum { O_FULL, O_SHORT } objectname;
 	} u;
 } *used_atom;
@@ -179,6 +186,21 @@ static void align_atom_parser(struct used_atom *atom, const char *arg)
 	string_list_clear(&params, 0);
 }
 
+static void if_atom_parser(struct used_atom *atom, const char *arg)
+{
+	if (!arg) {
+		atom->u.if_then_else.cmp_status = COMPARE_NONE;
+		return;
+	} else if (skip_prefix(arg, "equals=", &atom->u.if_then_else.str)) {
+		atom->u.if_then_else.cmp_status = COMPARE_EQUAL;
+	} else if (skip_prefix(arg, "notequals=", &atom->u.if_then_else.str)) {
+		atom->u.if_then_else.cmp_status = COMPARE_UNEQUAL;
+	} else {
+		die(_("unrecognized %%(if) argument: %s"), arg);
+	}
+}
+
+
 static struct {
 	const char *name;
 	cmp_type cmp_type;
@@ -220,7 +242,7 @@ static struct {
 	{ "color", FIELD_STR, color_atom_parser },
 	{ "align", FIELD_STR, align_atom_parser },
 	{ "end" },
-	{ "if" },
+	{ "if", FIELD_STR, if_atom_parser },
 	{ "then" },
 	{ "else" },
 };
@@ -422,6 +444,9 @@ static void if_atom_handler(struct atom_value *atomv, struct ref_formatting_stat
 	struct ref_formatting_stack *new;
 	struct if_then_else *if_then_else = xcalloc(sizeof(struct if_then_else), 1);
 
+	if_then_else->str = atomv->atom->u.if_then_else.str;
+	if_then_else->cmp_status = atomv->atom->u.if_then_else.cmp_status;
+
 	push_stack_element(&state->stack);
 	new = state->stack;
 	new->at_end = if_then_else_handler;
@@ -453,10 +478,17 @@ static void then_atom_handler(struct atom_value *atomv, struct ref_formatting_st
 		die(_("format: %%(then) atom used after %%(else)"));
 	if_then_else->then_atom_seen = 1;
 	/*
-	 * If there exists non-empty string between the 'if' and
-	 * 'then' atom then the 'if' condition is satisfied.
+	 * If the 'equals' or 'notequals' attribute is used then
+	 * perform the required comparison. If not, only non-empty
+	 * strings satisfy the 'if' condition.
 	 */
-	if (cur->output.len && !is_empty(cur->output.buf))
+	if (if_then_else->cmp_status == COMPARE_EQUAL) {
+		if (!strcmp(if_then_else->str, cur->output.buf))
+			if_then_else->condition_satisfied = 1;
+	} else if (if_then_else->cmp_status == COMPARE_UNEQUAL) {
+		if (strcmp(if_then_else->str, cur->output.buf))
+			if_then_else->condition_satisfied = 1;
+	} else if (cur->output.len && !is_empty(cur->output.buf))
 		if_then_else->condition_satisfied = 1;
 	strbuf_reset(&cur->output);
 }
@@ -1158,7 +1190,11 @@ static void populate_value(struct ref_array_item *ref)
 		} else if (!strcmp(name, "end")) {
 			v->handler = end_atom_handler;
 			continue;
-		} else if (!strcmp(name, "if")) {
+		} else if (starts_with(name, "if")) {
+			const char *s;
+
+			if (skip_prefix(name, "if:", &s))
+				v->s = xstrdup(s);
 			v->handler = if_atom_handler;
 			continue;
 		} else if (!strcmp(name, "then")) {