[PATCH 1/3] git-compat-util: introduce skip_to_opt_val()

[Christian Couder <christian.couder@gmail.com>]

From: Christian Couder <christian.couder@gmail.com>

We often accept both a "--key" option and a "--key=<val>" option.

These options currently are parsed using something like:

if (!strcmp(arg, "--key")) {
	/* do something */
} else if (skip_prefix(arg, "--key=", &arg)) {
	/* do something with arg */
}

which is a bit cumbersome compared to just:

if (skip_to_opt_val(arg, "--key", &arg)) {
	/* do something with arg */
}

Note that, when using skip_to_opt_val(), it is not possible any more
to do something different when the first argument is exactly "--key"
than when it is exactly "--key=", but in most cases we already don't
make any difference, which is a good thing.

Note that "opt" in the function name actually means "optional" as
the function can be used to parse any "key=value" string where "key"
is also considered as valid, not just command line options.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
---
 git-compat-util.h | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

Another possibility would be to add a "const char *default"
argument to the function, and to do: 

	if (!*p) {
		*val = default;
		return 1;
	}

This could make the function more useful in some cases.

I also wonder if the function is too big to be inlined, and
in that case, in which file it should be added. 

diff --git a/git-compat-util.h b/git-compat-util.h
index cedad4d581..7ee040388f 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -534,6 +534,41 @@ static inline int ends_with(const char *str, const char *suffix)
 	return strip_suffix(str, suffix, &len);
 }
 
+/*
+ * If the string "str" is the same as the string in "prefix", then the "val"
+ * parameter is set to the empty string and 1 is returned.
+ * If the string "str" begins with the string found in "prefix" and then a
+ * "=" sign, then the "val" parameter is set to "str + strlen(prefix) + 1"
+ * (i.e., to the point in the string right after the prefix and the "=" sign),
+ * and 1 is returned.
+ *
+ * Otherwise, return 0 and leave "val" untouched.
+ *
+ * When we accept both a "--key" and a "--key=<val>" option, this function
+ * can be used instead of !strcmp(arg, "--key") and then
+ * skip_prefix(arg, "--key=", &arg) to parse such an option.
+ */
+static inline int skip_to_opt_val(const char *str, const char *prefix,
+				  const char **val)
+{
+	const char *p;
+
+	if (!skip_prefix(str, prefix, &p))
+		return 0;
+
+	if (!*p) {
+		*val = "";
+		return 1;
+	}
+
+	if (*p == '=') {
+		*val = p + 1;
+		return 1;
+	}
+
+	return 0;
+}
+
 #define SWAP(a, b) do {						\
 	void *_swap_a_ptr = &(a);				\
 	void *_swap_b_ptr = &(b);				\
-- 
2.15.1.271.g1a4e40aa5d.dirty