Merge branch 'kn/for-each-ref'

GSoC project to rebuild ref listing by branch and tag based on the
for-each-ref machinery.  This is its first part.

* kn/for-each-ref:
  ref-filter: make 'ref_array_item' use a FLEX_ARRAY for refname
  for-each-ref: introduce filter_refs()
  ref-filter: move code from 'for-each-ref'
  ref-filter: add 'ref-filter.h'
  for-each-ref: rename variables called sort to sorting
  for-each-ref: rename some functions and make them public
  for-each-ref: introduce 'ref_array_clear()'
  for-each-ref: introduce new structures for better organisation
  for-each-ref: rename 'refinfo' to 'ref_array_item'
  for-each-ref: clean up code
  for-each-ref: extract helper functions out of grab_single_ref()

Makefile

@@ -763,6 +763,7 @@ LIB_OBJS += reachable.o
 LIB_OBJS += read-cache.o
 LIB_OBJS += reflog-walk.o
 LIB_OBJS += refs.o
+LIB_OBJS += ref-filter.o
 LIB_OBJS += remote.o
 LIB_OBJS += replace_object.o
 LIB_OBJS += rerere.o

ref-filter.h

+#ifndef REF_FILTER_H
+#define REF_FILTER_H
+
+#include "sha1-array.h"
+#include "refs.h"
+#include "commit.h"
+#include "parse-options.h"
+
+/* Quoting styles */
+#define QUOTE_NONE 0
+#define QUOTE_SHELL 1
+#define QUOTE_PERL 2
+#define QUOTE_PYTHON 4
+#define QUOTE_TCL 8
+
+#define FILTER_REFS_INCLUDE_BROKEN 0x1
+#define FILTER_REFS_ALL 0x2
+
+struct atom_value {
+	const char *s;
+	unsigned long ul; /* used for sorting when not FIELD_STR */
+};
+
+struct ref_sorting {
+	struct ref_sorting *next;
+	int atom; /* index into used_atom array (internal) */
+	unsigned reverse : 1;
+};
+
+struct ref_array_item {
+	unsigned char objectname[20];
+	int flag;
+	const char *symref;
+	struct atom_value *value;
+	char refname[FLEX_ARRAY];
+};
+
+struct ref_array {
+	int nr, alloc;
+	struct ref_array_item **items;
+};
+
+struct ref_filter {
+	const char **name_patterns;
+};
+
+struct ref_filter_cbdata {
+	struct ref_array *array;
+	struct ref_filter *filter;
+};
+
+/*
+ * API for filtering a set of refs. Based on the type of refs the user
+ * has requested, we iterate through those refs and apply filters
+ * as per the given ref_filter structure and finally store the
+ * filtered refs in the ref_array structure.
+ */
+int filter_refs(struct ref_array *array, struct ref_filter *filter, unsigned int type);
+/*  Clear all memory allocated to ref_array */
+void ref_array_clear(struct ref_array *array);
+/*  Parse format string and sort specifiers */
+int parse_ref_filter_atom(const char *atom, const char *ep);
+/*  Used to verify if the given format is correct and to parse out the used atoms */
+int verify_ref_format(const char *format);
+/*  Sort the given ref_array as per the ref_sorting provided */
+void ref_array_sort(struct ref_sorting *sort, struct ref_array *array);
+/*  Print the ref using the given format and quote_style */
+void show_ref_array_item(struct ref_array_item *info, const char *format, int quote_style);
+/*  Callback function for parsing the sort option */
+int parse_opt_ref_sorting(const struct option *opt, const char *arg, int unset);
+/*  Default sort option based on refname */
+struct ref_sorting *ref_default_sorting(void);
+
+#endif /*  REF_FILTER_H  */