Merge branch 'cauthmann/git-lfs-checks' into 'master'

Build script: check if git-lfs works

See merge request veloren/veloren!455

common/build.rs

@@ -1,10 +1,13 @@
 use std::env;
 use std::fs::File;
+use std::io::Read;
 use std::io::Write;
 use std::path::Path;
+use std::path::PathBuf;
 use std::process::Command;
 
 fn main() {
+    // Get the current githash
     match Command::new("git")
         .args(&["rev-parse", "--short", "HEAD"])
         .output()
@@ -26,4 +29,33 @@ fn main() {
         },
         Err(e) => panic!("failed to retrieve current git commit hash: {}", e),
     }
+    // Check if git-lfs is working
+    let asset_path: PathBuf = ["..", "assets", "voxygen", "background", "bg_main.png"]
+        .iter()
+        .collect();
+    let asset_file = match File::open(&asset_path) {
+        Ok(file) => file,
+        Err(e) => panic!(
+            "failed to open asset file {}: {}",
+            asset_path.to_str().unwrap(),
+            e
+        ),
+    };
+    const LFS_MARKER: &[u8] = b"version https://git-lfs.github.com/spec/";
+    let mut buffer = Vec::new();
+    let bytes_read = asset_file
+        .take(LFS_MARKER.len() as u64)
+        .read_to_end(&mut buffer)
+        .expect("failed to read asset file");
+
+    if bytes_read == LFS_MARKER.len() && buffer == LFS_MARKER {
+        panic!(
+            "\n\nGit Large File Storage (git-lfs) has not been set up correctly.\n\
+             Most common reasons:\n\
+             \t- git-lfs was not installed before cloning this repository\n\
+             \t- this repository was not cloned from the primary gitlab mirror.\n\
+             \t  The github mirror does not support lfs.\n\
+             See the book at https://book.veloren.net/ for details.\n\n"
+        );
+    }
 }