libfmt: Add %v for libobj to implement

3 files changed, 29 insertions, 0 deletions

diff --git a/libfmt/CMakeLists.txt b/libfmt/CMakeLists.txt
index b8db764..2d44c03 100644
--- a/libfmt/CMakeLists.txt
+++ b/libfmt/CMakeLists.txt
@@ -7,8 +7,10 @@ add_library(libfmt INTERFACE)
 target_include_directories(libfmt SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/include)
 target_sources(libfmt INTERFACE
 	libmisc.c
+	libobj.c
 )
 target_link_libraries(libfmt INTERFACE
 	pico_fmt
 	libmisc
+	libobj
 )
diff --git a/libfmt/include/libfmt/fmt.h b/libfmt/include/libfmt/fmt.h
index 3f2d4e7..4dba82f 100644
--- a/libfmt/include/libfmt/fmt.h
+++ b/libfmt/include/libfmt/fmt.h
@@ -10,4 +10,14 @@
 #include <pico/fmt_printf.h>
 #include <pico/fmt_install.h>
 
+#include <libobj/obj.h>
+
+/**
+ * An object that implements fmt_formatter can be printed using
+ * `printf("%v", boxed_obj)`.
+ */
+#define fmt_formatter_LO_IFACE \
+	LO_FUNC(void, format, struct fmt_state *)
+LO_INTERFACE(fmt_formatter)
+
 #endif /* _LIBFMT_FMT_H_ */
diff --git a/libfmt/libobj.c b/libfmt/libobj.c
new file mode 100644
index 0000000..e4b833b
--- /dev/null
+++ b/libfmt/libobj.c
@@ -0,0 +1,17 @@
+/* libfmt/libobj.c - Integrate pico-fmt with libobj
+ *
+ * Copyright (C) 2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#include <libfmt/fmt.h>
+
+static void libfmt_conv_formatter(struct fmt_state *state) {
+	lo_interface fmt_formatter obj = va_arg(*state->args, lo_interface fmt_formatter);
+	LO_CALL(obj, format, state);
+}
+
+[[gnu::constructor]]
+static void libfmt_install_formatter(void) {
+	fmt_install('v', libfmt_conv_formatter);
+}