argv-array: move doc to argv-array.h

Move the documentation from Documentation/technical/api-argv-array.txt
to argv-array.h as it's easier for the developers to find the usage
information beside the code instead of looking for it in another doc file.

Also documentation/technical/api-argv-array.txt is removed because the
information it has is now redundant and it'll be hard to keep it up to
date and synchronized with the documentation in the header file.

Signed-off-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: HebaWaly

Documentation/technical/api-argv-array.txt

@@ -1,8 +1,32 @@
 #ifndef ARGV_ARRAY_H
 #define ARGV_ARRAY_H
 
+/**
+ * The argv-array API allows one to dynamically build and store
+ * NULL-terminated lists.  An argv-array maintains the invariant that the
+ * `argv` member always points to a non-NULL array, and that the array is
+ * always NULL-terminated at the element pointed to by `argv[argc]`. This
+ * makes the result suitable for passing to functions expecting to receive
+ * argv from main().
+ *
+ * The string-list API (documented in string-list.h) is similar, but cannot be
+ * used for these purposes; instead of storing a straight string pointer,
+ * it contains an item structure with a `util` field that is not compatible
+ * with the traditional argv interface.
+ *
+ * Each `argv_array` manages its own memory. Any strings pushed into the
+ * array are duplicated, and all memory is freed by argv_array_clear().
+ */
+
 extern const char *empty_argv[];
 
+/**
+ * A single array. This should be initialized by assignment from
+ * `ARGV_ARRAY_INIT`, or by calling `argv_array_init`. The `argv`
+ * member contains the actual array; the `argc` member contains the
+ * number of elements in the array, not including the terminating
+ * NULL.
+ */
 struct argv_array {
 	const char **argv;
 	int argc;
@@ -11,17 +35,55 @@ struct argv_array {
 
 #define ARGV_ARRAY_INIT { empty_argv, 0, 0 }
 
+/**
+ * Initialize an array. This is no different than assigning from
+ * `ARGV_ARRAY_INIT`.
+ */
 void argv_array_init(struct argv_array *);
+
+/* Push a copy of a string onto the end of the array. */
 const char *argv_array_push(struct argv_array *, const char *);
+
+/**
+ * Format a string and push it onto the end of the array. This is a
+ * convenience wrapper combining `strbuf_addf` and `argv_array_push`.
+ */
 __attribute__((format (printf,2,3)))
 const char *argv_array_pushf(struct argv_array *, const char *fmt, ...);
+
+/**
+ * Push a list of strings onto the end of the array. The arguments
+ * should be a list of `const char *` strings, terminated by a NULL
+ * argument.
+ */
 LAST_ARG_MUST_BE_NULL
 void argv_array_pushl(struct argv_array *, ...);
+
+/* Push a null-terminated array of strings onto the end of the array. */
 void argv_array_pushv(struct argv_array *, const char **);
+
+/**
+ * Remove the final element from the array. If there are no
+ * elements in the array, do nothing.
+ */
 void argv_array_pop(struct argv_array *);
+
 /* Splits by whitespace; does not handle quoted arguments! */
 void argv_array_split(struct argv_array *, const char *);
+
+/**
+ * Free all memory associated with the array and return it to the
+ * initial, empty state.
+ */
 void argv_array_clear(struct argv_array *);
+
+/**
+ * Disconnect the `argv` member from the `argv_array` struct and
+ * return it. The caller is responsible for freeing the memory used
+ * by the array, and by the strings it references. After detaching,
+ * the `argv_array` is in a reinitialized state and can be pushed
+ * into again.
+ */
 const char **argv_array_detach(struct argv_array *);
 
 #endif /* ARGV_ARRAY_H */