examples: add a basic for-each-ref example

This is quite close to running "git for-each-ref" except:

  1. It does not take any formatting or selection options at
     all.

  2. The output is not sorted.

I wrote it to look at debugging some issues with ref
iteration, but there's no reason it can't live on as an
example command.

examples/.gitignore

@@ -9,4 +9,5 @@ log
 rev-parse
 status
 tag
+for-each-ref
 *.dSYM

examples/Makefile

@@ -4,6 +4,7 @@ CC = gcc
 CFLAGS = -g -I../include -I../src -Wall -Wextra -Wmissing-prototypes -Wno-missing-field-initializers
 LFLAGS = -L../build -lgit2 -lz
 APPS = general showindex diff rev-list cat-file status log rev-parse init blame tag
+APPS += for-each-ref
 
 all: $(APPS)
 

examples/for-each-ref.c

+#include <git2.h>
+#include <stdio.h>
+#include "common.h"
+
+static int show_ref(git_reference *ref, void *data)
+{
+        git_repository *repo = data;
+        git_reference *resolved = NULL;
+        char hex[GIT_OID_HEXSZ+1];
+        const git_oid *oid;
+        git_object *obj;
+
+        if (git_reference_type(ref) == GIT_REF_SYMBOLIC)
+                check_lg2(git_reference_resolve(&resolved, ref),
+                          "Unable to resolve symbolic reference",
+                          git_reference_name(ref));
+
+        oid = git_reference_target(resolved ? resolved : ref);
+        git_oid_fmt(hex, oid);
+        hex[GIT_OID_HEXSZ] = 0;
+        check_lg2(git_object_lookup(&obj, repo, oid, GIT_OBJ_ANY),
+                  "Unable to lookup object", hex);
+
+        printf("%s %-6s\t%s\n",
+               hex,
+               git_object_type2string(git_object_type(obj)),
+               git_reference_name(ref));
+
+        if (resolved)
+                git_reference_free(resolved);
+        return 0;
+}
+
+int main(int argc, char **argv)
+{
+        git_repository *repo;
+
+        if (argc != 1 || argv[1] /* silence -Wunused-parameter */)
+                fatal("Sorry, no for-each-ref options supported yet", NULL);
+
+        check_lg2(git_repository_open(&repo, "."),
+                  "Could not open repository", NULL);
+        check_lg2(git_reference_foreach(repo, show_ref, repo),
+                  "Could not iterate over references", NULL);
+        return 0;
+}