Add verify_state to ggml/sys/build.rs

Helps newbies like me set up the repo correctly.

crates/ggml/sys/build.rs

@@ -5,6 +5,8 @@ use std::path::{Path, PathBuf};
 // the host and target are the same. If they are not, it will turn off auto-feature-detection,
 // and you will need to manually specify target features through target-features.
 fn main() {
+ verify_state();
+
  println!("cargo:rerun-if-changed=llama-cpp");
 
  let mut builder = cc::Build::new();
@@ -104,6 +106,14 @@ fn main() {
  }
 }
 
+/// Verify the state of the repo to catch common newbie mistakes.
+fn verify_state() {
+ assert!(
+ Path::new("llama-cpp/ggml.c").exists(),
+ "Could not find llama-cpp/ggml.c. Try running `git submodule update --init`"
+ );
+}
+
 fn cfg_cublas() -> bool {
  !cfg!(target_os = "macos") && cfg!(feature = "cublas")
 }