[PATCH 2/2] pretty=format: Avoid some expensive calculations when not needed

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Use the new function interp_find_active() to avoid calculating the
unique hash names, and other things, when they are not even asked for.

Unfortunately, we cannot reuse the result of that function, which
would be cleaner: there are more users than just git log.  Most
notably, git-archive with "$Format:...$" substitution.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 pretty.c |   55 ++++++++++++++++++++++++++++++++++---------------------
 1 files changed, 34 insertions(+), 21 deletions(-)

diff --git a/pretty.c b/pretty.c
index 490cede..590de4c 100644
--- a/pretty.c
+++ b/pretty.c
@@ -394,6 +394,8 @@ void format_commit_message(const struct commit *commit,
 	enum { HEADER, SUBJECT, BODY } state;
 	const char *msg = commit->buffer;
 
+	interp_find_active(format, table, ARRAY_SIZE(table));
+
 	if (ILEFT_RIGHT + 1 != ARRAY_SIZE(table))
 		die("invalid interp table!");
 
@@ -407,12 +409,18 @@ void format_commit_message(const struct commit *commit,
 	/* these depend on the commit */
 	if (!commit->object.parsed)
 		parse_object(commit->object.sha1);
-	interp_set_entry(table, IHASH, sha1_to_hex(commit->object.sha1));
-	interp_set_entry(table, IHASH_ABBREV,
+	if (table[IHASH].active)
+		interp_set_entry(table, IHASH,
+				sha1_to_hex(commit->object.sha1));
+	if (table[IHASH_ABBREV].active)
+		interp_set_entry(table, IHASH_ABBREV,
 			find_unique_abbrev(commit->object.sha1,
 				DEFAULT_ABBREV));
-	interp_set_entry(table, ITREE, sha1_to_hex(commit->tree->object.sha1));
-	interp_set_entry(table, ITREE_ABBREV,
+	if (table[ITREE].active)
+		interp_set_entry(table, ITREE,
+				sha1_to_hex(commit->tree->object.sha1));
+	if (table[ITREE_ABBREV].active)
+		interp_set_entry(table, ITREE_ABBREV,
 			find_unique_abbrev(commit->tree->object.sha1,
 				DEFAULT_ABBREV));
 	interp_set_entry(table, ILEFT_RIGHT,
@@ -422,22 +430,27 @@ void format_commit_message(const struct commit *commit,
 			 ? "<"
 			 : ">");
 
-	parents[1] = 0;
-	for (i = 0, p = commit->parents;
-			p && i < sizeof(parents) - 1;
-			p = p->next)
-		i += snprintf(parents + i, sizeof(parents) - i - 1, " %s",
-			sha1_to_hex(p->item->object.sha1));
-	interp_set_entry(table, IPARENTS, parents + 1);
-
-	parents[1] = 0;
-	for (i = 0, p = commit->parents;
-			p && i < sizeof(parents) - 1;
-			p = p->next)
-		i += snprintf(parents + i, sizeof(parents) - i - 1, " %s",
-			find_unique_abbrev(p->item->object.sha1,
-				DEFAULT_ABBREV));
-	interp_set_entry(table, IPARENTS_ABBREV, parents + 1);
+	if (table[IPARENTS].active) {
+		parents[1] = 0;
+		for (i = 0, p = commit->parents;
+				p && i < sizeof(parents) - 1;
+				p = p->next)
+			i += snprintf(parents + i, sizeof(parents) - i - 1,
+				" %s", sha1_to_hex(p->item->object.sha1));
+		interp_set_entry(table, IPARENTS, parents + 1);
+	}
+
+	if (table[IPARENTS_ABBREV].active) {
+		parents[1] = 0;
+		for (i = 0, p = commit->parents;
+				p && i < sizeof(parents) - 1;
+				p = p->next)
+			i += snprintf(parents + i, sizeof(parents) - i - 1,
+				" %s",
+				find_unique_abbrev(p->item->object.sha1,
+					DEFAULT_ABBREV));
+		interp_set_entry(table, IPARENTS_ABBREV, parents + 1);
+	}
 
 	for (i = 0, state = HEADER; msg[i] && state < BODY; i++) {
 		int eol;
@@ -464,7 +477,7 @@ void format_commit_message(const struct commit *commit,
 				xmemdupz(msg + i + 9, eol - i - 9);
 		i = eol;
 	}
-	if (msg[i])
+	if (table[IBODY].active && msg[i])
 		table[IBODY].value = xstrdup(msg + i);
 
 	len = interpolate(sb->buf + sb->len, strbuf_avail(sb),
-- 
1.5.3.5.1597.g7191