Clean up diff implementation for review

This fixes several bugs, updates tests and docs, eliminates the
FILE* assumption in favor of printing callbacks for the diff patch
formatter helpers, and adds a "diff" example function that can
perform a diff from the command line.

1 files changed, 134 insertions, 0 deletions

diff --git a/examples/diff.c b/examples/diff.c
new file mode 100644
index 000000000..9b696dad5
--- /dev/null
+++ b/examples/diff.c
@@ -0,0 +1,134 @@
+#include <stdio.h>
+#include <git2.h>
+#include <stdlib.h>
+#include <string.h>
+
+void check(int error, const char *message)
+{
+	if (error) {
+		fprintf(stderr, "%s (%d)\n", message, error);
+		exit(1);
+	}
+}
+
+int resolve_to_tree(git_repository *repo, const char *identifier, git_tree **tree)
+{
+	int err = 0;
+	size_t len = strlen(identifier);
+	git_oid oid;
+	git_object *obj = NULL;
+
+	/* try to resolve as OID */
+	if (git_oid_fromstrn(&oid, identifier, len) == 0)
+		git_object_lookup_prefix(&obj, repo, &oid, len, GIT_OBJ_ANY);
+
+	/* try to resolve as reference */
+	if (obj == NULL) {
+		git_reference *ref, *resolved;
+		if (git_reference_lookup(&ref, repo, identifier) == 0) {
+			git_reference_resolve(&resolved, ref);
+			git_reference_free(ref);
+			if (resolved) {
+				git_object_lookup(&obj, repo, git_reference_oid(resolved), GIT_OBJ_ANY);
+				git_reference_free(resolved);
+			}
+		}
+	}
+
+	if (obj == NULL)
+		return GIT_ENOTFOUND;
+
+	switch (git_object_type(obj)) {
+	case GIT_OBJ_TREE:
+		*tree = (git_tree *)obj;
+		break;
+	case GIT_OBJ_COMMIT:
+		err = git_commit_tree(tree, (git_commit *)obj);
+		git_object_free(obj);
+		break;
+	default:
+		err = GIT_ENOTFOUND;
+	}
+
+	return err;
+}
+
+char *colors[] = {
+	"\033[m", /* reset */
+	"\033[1m", /* bold */
+	"\033[31m", /* red */
+	"\033[32m", /* green */
+	"\033[36m" /* cyan */
+};
+
+int printer(void *data, char usage, const char *line)
+{
+	int *last_color = data, color = 0;
+
+	if (*last_color >= 0) {
+		switch (usage) {
+		case GIT_DIFF_LINE_ADDITION: color = 3; break;
+		case GIT_DIFF_LINE_DELETION: color = 2; break;
+		case GIT_DIFF_LINE_ADD_EOFNL: color = 3; break;
+		case GIT_DIFF_LINE_DEL_EOFNL: color = 2; break;
+		case GIT_DIFF_LINE_FILE_HDR: color = 1; break;
+		case GIT_DIFF_LINE_HUNK_HDR: color = 4; break;
+		default: color = 0;
+		}
+		if (color != *last_color) {
+			if (*last_color == 1 || color == 1)
+				fputs(colors[0], stdout);
+			fputs(colors[color], stdout);
+			*last_color = color;
+		}
+	}
+
+	fputs(line, stdout);
+	return 0;
+}
+
+int main(int argc, char *argv[])
+{
+	char path[GIT_PATH_MAX];
+	git_repository *repo = NULL;
+	git_tree *a, *b;
+	git_diff_options opts = {0};
+	git_diff_list *diff;
+	char *dir = ".";
+	int color = -1;
+
+	if (argc != 3) {
+		fprintf(stderr, "usage: diff <tree-oid> <tree-oid>\n");
+		exit(1);
+	}
+
+	check(git_repository_discover(path, sizeof(path), dir, 0, "/"),
+		"Could not discover repository");
+	check(git_repository_open(&repo, path),
+		"Could not open repository");
+
+	check(resolve_to_tree(repo, argv[1], &a), "Looking up first tree");
+	check(resolve_to_tree(repo, argv[2], &b), "Looking up second tree");
+
+	check(git_diff_tree_to_tree(repo, &opts, a, b, &diff), "Generating diff");
+
+	fputs(colors[0], stdout);
+
+	check(git_diff_print_compact(diff, &color, printer), "Displaying diff summary");
+
+	fprintf(stdout, "--\n");
+
+	color = 0;
+
+	check(git_diff_print_patch(diff, &color, printer), "Displaying diff");
+
+	fputs(colors[0], stdout);
+
+	git_diff_list_free(diff);
+	git_tree_free(a);
+	git_tree_free(b);
+	git_repository_free(repo);
+
+	return 0;
+}
+