grep: copy struct in one fell swoop

We have a `struct grep_opt` with our defaults which we then copy into
the caller's struct. Rather than zeroing the target struct and copying
each element one by one, just copy everything at once. This leaves the
code simpler and more maintainable.

We don't have any ownership issues with what we're copying now and can
just greedily copy the whole thing. If and when we do need to handle
such elements (`char *`?), we must and can handle it appropriately. Make
sure to leave a comment to our future selves.

Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

grep.c

@@ -66,11 +66,6 @@ static const char *color_grep_slots[] = {
 	[GREP_COLOR_SEP]	    = "separator",
 };
 
-static void color_set(char *dst, const char *color_bytes)
-{
-	xsnprintf(dst, COLOR_MAXLEN, "%s", color_bytes);
-}
-
 static int parse_pattern_type_arg(const char *opt, const char *arg)
 {
 	if (!strcmp(arg, "default"))
@@ -100,6 +95,14 @@ int grep_config(const char *var, const char *value, void *cb)
 	if (userdiff_config(var, value) < 0)
 		return -1;
 
+	/*
+	 * The instance of grep_opt that we set up here is copied by
+	 * grep_init() to be used by each individual invocation.
+	 * When populating a new field of this structure here, be
+	 * sure to think about ownership -- e.g., you might need to
+	 * override the shallow copy in grep_init() with a deep copy.
+	 */
+
 	if (!strcmp(var, "grep.extendedregexp")) {
 		opt->extended_regexp_option = git_config_bool(var, value);
 		return 0;
@@ -157,9 +160,6 @@ int grep_config(const char *var, const char *value, void *cb)
  */
 void grep_init(struct grep_opt *opt, struct repository *repo, const char *prefix)
 {
-	struct grep_opt *def = &grep_defaults;
-	int i;
-
 #if defined(USE_LIBPCRE2)
 	if (!pcre2_global_context)
 		pcre2_global_context = pcre2_general_context_create(
@@ -171,26 +171,13 @@ void grep_init(struct grep_opt *opt, struct repository *repo, const char *prefix
 	pcre_free = free;
 #endif
 
-	memset(opt, 0, sizeof(*opt));
+	*opt = grep_defaults;
+
 	opt->repo = repo;
 	opt->prefix = prefix;
 	opt->prefix_length = (prefix && *prefix) ? strlen(prefix) : 0;
 	opt->pattern_tail = &opt->pattern_list;
 	opt->header_tail = &opt->header_list;
-
-	opt->only_matching = def->only_matching;
-	opt->color = def->color;
-	opt->extended_regexp_option = def->extended_regexp_option;
-	opt->pattern_type_option = def->pattern_type_option;
-	opt->linenum = def->linenum;
-	opt->columnnum = def->columnnum;
-	opt->max_depth = def->max_depth;
-	opt->pathname = def->pathname;
-	opt->relative = def->relative;
-	opt->output = def->output;
-
-	for (i = 0; i < NR_GREP_COLORS; i++)
-		color_set(opt->colors[i], def->colors[i]);
 }
 
 void grep_destroy(void)