meta: add ivy-diag library

ivy-diag is used for generating and emitting diagnostic messages during compilation.

diag/write.c

@@ -0,0 +1,26 @@
+#include "write.h"
+
+#include <ivy/diag.h>
+
+extern struct diag_writer pretty_writer;
+
+static const struct diag_writer *writers[] = {
+	[IVY_DIAG_FORMAT_PRETTY] = &pretty_writer,
+};
+static const size_t nr_writers = sizeof writers / sizeof writers[0];
+
+enum ivy_status diag_write(
+	struct ivy_diag_ctx *ctx, struct ivy_diag *diag,
+	enum ivy_diag_format format, struct ivy_diag_stream *stream)
+{
+	if (format < 0 || format >= nr_writers) {
+		return IVY_ERR_INVALID_VALUE;
+	}
+
+	const struct diag_writer *writer = writers[format];
+	if (!writer) {
+		return IVY_ERR_INVALID_VALUE;
+	}
+
+	return writer->write(ctx, diag, stream);
+}