Okay, it builds!

bazel/wrlib/BUILD.bazel

@@ -5,6 +5,7 @@ rust_library(
     srcs = ["wrlib.rs"],
     deps = [":wrlib"],
     visibility = ["//visibility:public"],
+    edition = "2021",
 )
 
 cc_library(

bazel/wrlib/wrlib.rs

@@ -1,6 +1,6 @@
-use std::os::raw::{c_char, c_int, c_uchar};
+use std::os::raw::{c_char, c_int, c_uchar, c_ulong};
 
-#[repr(u8)]
+#[repr(C)]
 pub enum RImageFormat {
     RGBAFormat = 0,
     RRGBAFormat = 1,
@@ -15,12 +15,60 @@ pub struct RImage {
     ref_count: c_int,
 }
 
+#[repr(C)]
+pub struct RContext {
+    // display: *mut Display,
+    display: usize,
+    screen_number: c_int,
+    // cmap: Colormap,
+
+    // attribs: *mut RContextAttributes,
+    attribs: usize,
+
+    // copy_gc: GC,
+
+    // visual: *mut Visual,
+    visual: usize,
+    depth: c_int,
+    // drawable: Window,
+    vclass: c_int,
+
+    black: c_ulong,
+    white: c_ulong,
+
+    red_offset: c_int,
+    green_offset: c_int,
+    blue_offset: c_int,
+
+    std_rgb_map: usize,
+    std_gray_map: usize,
+    // std_rgb_map: *mut XStandardColorMap,
+    // std_gray_map: *mut XStandardColorMap,
+
+    ncolors: c_int,
+    colors: usize,
+    // colors: *mut XColor,
+    pixels: *mut c_ulong,
+
+    flags: u8,
+}
+
+#[repr(C)]
+pub enum RScalingFilter {
+    RBoxFilter,
+    RTriangleFilter,
+    RBellFilter,
+    RBSplineFilter,
+    RLanczos3Filter,
+    RMitchellFilter,
+}
+
 extern "C" {
     pub fn r_destroy_conversion_tables() -> ();
 
     pub fn RLoadPPM(file: *const c_char) -> *mut RImage;
 
-    pub fn RLoadXPM(context: *mut RContext, file: *const c_char) -> mut *RImage;
+    pub fn RLoadXPM(context: *mut RContext, file: *const c_char) -> *mut RImage;
 
     pub fn RReleaseCache() -> ();