Update macro to use relative working dirs, Spans

libm/src/lib.rs

@@ -1,3 +1,4 @@
+#![feature(proc_macro_span)]
 #![warn(
     clippy::correctness,
     clippy::nursery,
@@ -12,18 +13,32 @@
 use std::fs::File;
 use std::io::{Read, Seek, SeekFrom};
 
-use proc_macro::TokenStream;
+use proc_macro::{Span, TokenStream};
 use quote::quote;
+use std::path::PathBuf;
 use syn::{LitStr, parse_macro_input};
-
 extern crate proc_macro;
 
 #[proc_macro]
+/// Expects the file path to be relative to the current file so this works
+/// similarly to the standard Rust include! macros.
 pub fn include_font(item: TokenStream) -> TokenStream {
-    let filename = parse_macro_input!(item as LitStr);
-    let file_path = filename.value();
+    let span = Span::call_site();
+    let source_file = span.source_file();
 
-    println!("Loading font: [{}]", file_path);
+    if !source_file.is_real() {
+        panic!(
+            "We can't handle finding files if the source file does not exist. TODO: Can we?"
+        )
+    }
+
+    let filename = parse_macro_input!(item as LitStr);
+    let source_filepath: PathBuf = source_file.path();
+    let file_path = format!(
+        "{}/{}",
+        source_filepath.parent().unwrap_or_else(|| panic!("Expected to find the calling source file in a folder like src! Got: {}", source_filepath.display())).display(),
+        filename.value()
+    );
 
     let font_bytes = match load_file(file_path) {
         Ok(bytes) => bytes,