toolchain: add a program for compiling ipc interface definitions

ifc can be used to compile .if files into self-contained header-only C
libraries, which can be used to send/receive messages that conform
to the described interface.

toolchain/ifc/line-source.h

@@ -0,0 +1,39 @@
+#ifndef LINE_SOURCE_H_
+#define LINE_SOURCE_H_
+
+#include "file-span.h"
+#include "status.h"
+
+#include <blue/core/stream.h>
+#include <blue/ds/array.h>
+#include <blue/ds/string.h>
+
+struct line_source {
+	b_stream *s_stream;
+	const char *s_path;
+	b_string *s_linebuf;
+	b_iterator *s_linebuf_ptr;
+	b_array *s_lines;
+
+	struct file_cell s_cursor;
+};
+
+extern enum status line_source_init(
+	struct line_source *src,
+	const char *path,
+	b_stream *stream);
+extern void line_source_cleanup(struct line_source *src);
+
+extern const char *line_source_get_path(const struct line_source *src);
+extern const struct file_cell *line_source_get_cursor(
+	const struct line_source *src);
+extern b_wchar line_source_peekc(struct line_source *src);
+extern b_wchar line_source_getc(struct line_source *src);
+extern enum status line_source_get_row(
+	struct line_source *src,
+	size_t row,
+	const b_string **out);
+
+extern bool line_source_input_available(struct line_source *src);
+
+#endif