context: copy symlinks as symlinks and improve error messages

src/build.rs

@@ -46,10 +46,23 @@ pub fn build_source_package(cwd: Option<&Path>) -> Result<(), Box<dyn Error>> {
         );
     }
 
-    let status = command.status()?;
+    let status = command.status().map_err(|e| {
+        format!(
+            "Failed to run 'dpkg-buildpackage': {}. \
+             Is 'dpkg-dev' (which provides dpkg-buildpackage) installed?",
+            e
+        )
+    })?;
 
     if !status.success() {
-        return Err(format!("dpkg-buildpackage failed with status: {}", status).into());
+        return Err(format!(
+            "dpkg-buildpackage failed with status: {}. \
+             Re-run with 'RUST_LOG=debug' for more details, or run \
+             'dpkg-buildpackage -S -I -i -nc -d' manually in '{}' to see the full output.",
+            status,
+            cwd.display()
+        )
+        .into());
     }
 
     if signing_key.is_some() {