use relative path for rust_crate_sources

crates/codegen/bin/print_source.rs

@@ -3,12 +3,23 @@ use codegen::packages_source;
 use codegen::with_enabled_crates_all;
 use codegen::BuildError;
 use std::io::Write;
+use std::path::PathBuf;
 
 /// First we have to generate the include file for the main crate which
 /// will be stored in OUT_DIR. It only contains the rust_init_syms
 /// that runs the crates *_init_syms functions.
 pub fn generate_source_list(packages: Vec<&Package>) -> Result<(), BuildError> {
+    let abs_top_srcdir = std::env::var("ABS_TOP_SRCDIR")
+        .map(|dir| PathBuf::from(dir))
+        .ok();
     for file in packages_source(packages) {
+        let file = match abs_top_srcdir {
+            Some(ref base) => {
+                let path = file.as_path().strip_prefix(base).unwrap().to_path_buf();
+                PathBuf::from("..").join(path)
+            }
+            None => file,
+        };
         write!(std::io::stdout(), "{} ", file.display())?;
     }
     Ok(())

src/Makefile.in

@@ -777,6 +777,7 @@ HEADERS=$(wildcard $(srcdir)/*.h)
 
 $(RUST_CRATES_SOURCES_FILE) : FORCE
 	cd ../crates/emacsng && \
+	ABS_TOP_SRCDIR=$(abs_top_srcdir) \
 	cargo run -p codegen --bin print-source $(CARGO_FEATURES) > $$OLDPWD/$@
 
 $(LIBEMACSNG_ARCHIVE) : FORCE