Make the Store API more type-safe

Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.

Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.

Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).

1 files changed, 59 insertions, 29 deletions

diff --git a/nix-rust/src/c.rs b/nix-rust/src/c.rs
index 42ecb9866..4c1724eb3 100644
--- a/nix-rust/src/c.rs
+++ b/nix-rust/src/c.rs
@@ -1,6 +1,7 @@
 use super::{
     error,
     foreign::{self, CBox},
+    store::StorePath,
     util,
 };
 
@@ -13,43 +14,72 @@ pub extern "C" fn unpack_tarfile(
 }
 
 #[no_mangle]
-pub extern "C" fn rust_test() {
-    use crate::store::{self, Store};
-    use std::path::Path;
-    use tokio::runtime::Runtime;
+pub unsafe extern "C" fn ffi_String_new(s: &str, out: *mut String) {
+    // FIXME: check whether 's' is valid UTF-8?
+    out.write(s.to_string())
+}
 
-    let fut = async move {
-        let store: Box<dyn Store> = Box::new(store::BinaryCacheStore::new(
-            "http://cache.nixos.org".to_string(),
-        ));
+#[no_mangle]
+pub unsafe extern "C" fn ffi_String_drop(self_: *mut String) {
+    std::ptr::drop_in_place(self_);
+}
 
-        let path = store
-            .parse_store_path(&Path::new(
-                "/nix/store/7h7qgvs4kgzsn8a6rb273saxyqh4jxlz-konsole-18.12.3",
-            ))
-            .unwrap();
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_new(
+    path: &str,
+    store_dir: &str,
+) -> Result<StorePath, error::CppException> {
+    StorePath::new(std::path::Path::new(path), store_dir).map_err(|err| err.into())
+}
 
-        /*
-        let info = store.query_path_info(&path).await.unwrap();
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_new2(
+    hash: &[u8; crate::store::path::STORE_PATH_HASH_BYTES],
+    name: &str,
+) -> Result<StorePath, error::CppException> {
+    StorePath::from_parts(*hash, name).map_err(|err| err.into())
+}
 
-        eprintln!("INFO = {:?}", info);
-         */
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_fromBaseName(
+    base_name: &str,
+) -> Result<StorePath, error::CppException> {
+    StorePath::new_from_base_name(base_name).map_err(|err| err.into())
+}
 
-        let closure = store
-            .compute_path_closure(vec![path].into_iter().collect())
-            .await
-            .unwrap();
+#[no_mangle]
+pub unsafe extern "C" fn ffi_StorePath_drop(self_: *mut StorePath) {
+    std::ptr::drop_in_place(self_);
+}
 
-        eprintln!("CLOSURE = {:?}", closure.len());
-    };
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_to_string(self_: &StorePath) -> String {
+    format!("{}", self_)
+}
 
-    let rt = Runtime::new().unwrap();
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_less_than(a: &StorePath, b: &StorePath) -> bool {
+    a < b
+}
 
-    rt.block_on(fut);
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_eq(a: &StorePath, b: &StorePath) -> bool {
+    a == b
+}
 
-    /*
-    let file = std::fs::File::open("test.nar").unwrap();
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_clone(self_: &StorePath) -> StorePath {
+    self_.clone()
+}
 
-    crate::nar::parse(&mut std::io::BufReader::new(file)).unwrap();
-    */
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_name(self_: &StorePath) -> &str {
+    self_.name.name()
+}
+
+#[no_mangle]
+pub extern "C" fn ffi_StorePath_hash_data(
+    self_: &StorePath,
+) -> &[u8; crate::store::path::STORE_PATH_HASH_BYTES] {
+    self_.hash.hash()
 }