feat: Add nix-expr library, update nix

(cherry picked from commit bf1ddd1c9137578b86895577d5b80e0c5771b605)

flake.lock

@@ -173,11 +173,11 @@
         "nixpkgs-regression": "nixpkgs-regression"
       },
       "locked": {
-        "lastModified": 1705358697,
-        "narHash": "sha256-1SjVVJKIXfSoymtIBCx8mPkhw6LpyihrtzMXdFFOH2M=",
+        "lastModified": 1709227987,
+        "narHash": "sha256-ndFevohurD6MQCCBnOdHLDmsJ3vfpF5+cKizXvq5vmw=",
         "owner": "tweag",
         "repo": "nix",
-        "rev": "eb456d68bd22e1296c2eca30fa06281de0da289e",
+        "rev": "0fd441d0bf6331a1152cdc091724b4648d187f90",
         "type": "github"
       },
       "original": {

flake.nix

@@ -26,11 +26,8 @@
         perSystem = { config, self', inputs', pkgs, ... }: {
 
 
-          packages.nix = inputs'.nix.packages.nix.overrideAttrs {
-            # checkPhase does not seem to terminate.
-            # TODO: remove override
-            doCheck = false;
-          };
+          
+          packages.nix = inputs'.nix.packages.nix;
 
           pre-commit.settings.hooks.nixpkgs-fmt.enable = true;
           # Temporarily disable rustfmt due to configuration issues

rust/Cargo.lock

@@ -72,6 +72,16 @@ dependencies = [
  "libloading",
 ]
 
+[[package]]
+name = "ctor"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ad291aa74992b9b7a7e88c38acbbf6ad7e107f1d90ee8775b7bc1fc3394f485c"
+dependencies = [
+ "quote",
+ "syn",
+]
+
 [[package]]
 name = "either"
 version = "1.10.0"
@@ -172,6 +182,18 @@ dependencies = [
  "pkg-config",
 ]
 
+[[package]]
+name = "nix-expr"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "ctor",
+ "lazy_static",
+ "nix-c-raw",
+ "nix-store",
+ "nix-util",
+]
+
 [[package]]
 name = "nix-store"
 version = "0.1.0"

rust/Cargo.toml

@@ -1,6 +1,7 @@
 [workspace]
 members = [
     "nix-c-raw",
+    "nix-expr",
     "nix-util",
     "nix-store",
 ]

rust/nix-c-raw/build.rs

@@ -37,6 +37,14 @@ fn c_headers() -> Vec<String> {
         args.push(format!("-I{}", path.to_str().unwrap()));
     }
 
+    for path in pkg_config::probe_library("bdw-gc")
+        .unwrap()
+        .include_paths
+        .iter()
+    {
+        args.push(format!("-I{}", path.to_str().unwrap()));
+    }
+
     if let Ok(cflags) = std::env::var("RUST_NIX_C_RAW_EXTRA_CFLAGS") {
         for flag in cflags.split_whitespace() {
             args.push(flag.to_string());

rust/nix-c-raw/include/nix-c-raw.h

@@ -1,4 +1,6 @@
 #include <nix_api_util.h>
 #include <nix_api_store.h>
+#define GC_THREADS
+#include <gc/gc.h>
 #include <nix_api_expr.h>
 #include <nix_api_value.h>

rust/nix-expr/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "nix-expr"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+
+[dependencies]
+anyhow = "1.0.79"
+nix-store = { path = "../nix-store" }
+nix-util = { path = "../nix-util" }
+nix-c-raw = { path = "../nix-c-raw" }
+lazy_static = "1.4.0"
+ctor = "0.2.7"

rust/nix-expr/src/eval_state.rs

@@ -0,0 +1,265 @@
+use crate::value::{Value, ValueType};
+use anyhow::Context as _;
+use anyhow::{bail, Result};
+use lazy_static::lazy_static;
+use nix_c_raw as raw;
+use nix_store::store::Store;
+use nix_util::context::Context;
+use std::ffi::CString;
+use std::ptr::null_mut;
+use std::ptr::NonNull;
+
+lazy_static! {
+    static ref INIT: Result<()> = {
+        unsafe {
+            raw::GC_allow_register_threads();
+        }
+        let context: Context = Context::new();
+        unsafe {
+            raw::nix_libexpr_init(context.ptr());
+        }
+        context.check_err()?;
+        Ok(())
+    };
+}
+pub fn init() -> Result<()> {
+    let x = INIT.as_ref();
+    match x {
+        Ok(_) => Ok(()),
+        Err(e) => {
+            // Couldn't just clone the error, so we have to print it here.
+            Err(anyhow::format_err!("nix_libstore_init error: {}", e))
+        }
+    }
+}
+
+pub struct EvalState {
+    eval_state: NonNull<raw::EvalState>,
+    store: Store,
+    context: Context,
+}
+impl EvalState {
+    pub fn new(store: Store) -> Result<Self> {
+        let context = Context::new();
+
+        init()?;
+
+        let eval_state = unsafe {
+            raw::nix_state_create(
+                context.ptr(),
+                /* searchPath */ null_mut(),
+                store.raw_ptr(),
+            )
+        };
+        if eval_state.is_null() {
+            bail!("nix_state_create returned a null pointer");
+        }
+        Ok(EvalState {
+            eval_state: NonNull::new(eval_state).unwrap(),
+            store,
+            context,
+        })
+    }
+    pub fn raw_ptr(&self) -> *mut raw::EvalState {
+        self.eval_state.as_ptr()
+    }
+    pub fn store(&self) -> &Store {
+        &self.store
+    }
+    pub fn eval_from_string(&self, expr: String, path: String) -> Result<Value> {
+        let expr_ptr =
+            CString::new(expr).with_context(|| "eval_from_string: expr contains null byte")?;
+        let path_ptr =
+            CString::new(path).with_context(|| "eval_from_string: path contains null byte")?;
+        let value = self.new_value_uninitialized();
+        unsafe {
+            let ctx_ptr = self.context.ptr();
+            raw::nix_expr_eval_from_string(
+                ctx_ptr,
+                self.raw_ptr(),
+                expr_ptr.as_ptr(),
+                path_ptr.as_ptr(),
+                value.raw_ptr(),
+            );
+        };
+        self.context.check_err()?;
+        Ok(value)
+    }
+    /** Try turn any Value into a Value that isn't a Thunk. */
+    pub fn force(&self, v: &Value) -> Result<()> {
+        unsafe {
+            raw::nix_value_force(self.context.ptr(), self.raw_ptr(), v.raw_ptr());
+        }
+        self.context.check_err()
+    }
+    pub fn value_is_thunk(&self, value: &Value) -> bool {
+        let r = unsafe {
+            raw::nix_get_type(self.context.ptr(), value.raw_ptr()) == raw::ValueType_NIX_TYPE_THUNK
+        };
+        self.context.check_err().unwrap();
+        r
+    }
+    pub fn value_type(&self, value: &Value) -> Result<ValueType> {
+        if self.value_is_thunk(value) {
+            self.force(value)?;
+        }
+        let r = unsafe { raw::nix_get_type(self.context.ptr(), value.raw_ptr()) };
+        Ok(ValueType::from_raw(r))
+    }
+
+    fn new_value_uninitialized(&self) -> Value {
+        let value = unsafe { raw::nix_alloc_value(self.context.ptr(), self.raw_ptr()) };
+        Value::new(value)
+    }
+}
+
+pub fn gc_now() {
+    unsafe {
+        raw::nix_gc_now();
+    }
+}
+
+/** Run a function while making sure that the current thread is registered with the GC. */
+pub fn gc_registering_current_thread<F, R>(f: F) -> Result<R>
+where
+    F: FnOnce() -> R,
+{
+    init()?;
+    if unsafe { raw::GC_thread_is_registered() } != 0 {
+        return Ok(f());
+    } else {
+        gc_register_my_thread().unwrap();
+        let r = f();
+        unsafe {
+            raw::GC_unregister_my_thread();
+        }
+        return Ok(r);
+    }
+}
+
+pub fn gc_register_my_thread() -> Result<()> {
+    unsafe {
+        let already_done = raw::GC_thread_is_registered();
+        if already_done != 0 {
+            return Ok(());
+        }
+        let mut sb: raw::GC_stack_base = raw::GC_stack_base {
+            mem_base: 0 as *mut _,
+        };
+        let r = raw::GC_get_stack_base(&mut sb);
+        if r as u32 != raw::GC_SUCCESS {
+            Err(anyhow::format_err!("GC_get_stack_base failed: {}", r))?;
+        }
+        raw::GC_register_my_thread(&sb);
+        Ok(())
+    }
+}
+
+impl Drop for EvalState {
+    fn drop(&mut self) {
+        unsafe {
+            raw::nix_state_free(self.raw_ptr());
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use ctor::ctor;
+
+    use super::*;
+
+    #[ctor]
+    fn setup() {
+        init().unwrap();
+    }
+
+    #[test]
+    fn eval_state_new_and_drop() {
+        gc_registering_current_thread(|| {
+            // very basic test: make sure initialization doesn't crash
+            let store = Store::open("auto").unwrap();
+            let _e = EvalState::new(store).unwrap();
+        })
+        .unwrap();
+    }
+
+    #[test]
+    fn eval_state_eval_from_string() {
+        gc_registering_current_thread(|| {
+            let store = Store::open("auto").unwrap();
+            let es = EvalState::new(store).unwrap();
+            let v = es
+                .eval_from_string("1".to_string(), "<test>".to_string())
+                .unwrap();
+            let v2 = v.clone();
+            es.force(&v).unwrap();
+            let t = es.value_type(&v).unwrap();
+            assert!(t == ValueType::Int);
+            let t2 = es.value_type(&v2).unwrap();
+            assert!(t2 == ValueType::Int);
+            gc_now();
+        })
+        .unwrap();
+    }
+
+    #[test]
+    fn eval_state_value_bool() {
+        gc_registering_current_thread(|| {
+            let store = Store::open("auto").unwrap();
+            let es = EvalState::new(store).unwrap();
+            let v = es
+                .eval_from_string("true".to_string(), "<test>".to_string())
+                .unwrap();
+            es.force(&v).unwrap();
+            let t = es.value_type(&v).unwrap();
+            assert!(t == ValueType::Bool);
+        })
+        .unwrap();
+    }
+
+    #[test]
+    fn eval_state_value_string() {
+        gc_registering_current_thread(|| {
+            let store = Store::open("auto").unwrap();
+            let es = EvalState::new(store).unwrap();
+            let v = es
+                .eval_from_string("\"hello\"".to_string(), "<test>".to_string())
+                .unwrap();
+            es.force(&v).unwrap();
+            let t = es.value_type(&v).unwrap();
+            assert!(t == ValueType::String);
+        })
+        .unwrap();
+    }
+
+    #[test]
+    fn eval_state_value_attrset() {
+        gc_registering_current_thread(|| {
+            let store = Store::open("auto").unwrap();
+            let es = EvalState::new(store).unwrap();
+            let v = es
+                .eval_from_string("{ }".to_string(), "<test>".to_string())
+                .unwrap();
+            es.force(&v).unwrap();
+            let t = es.value_type(&v).unwrap();
+            assert!(t == ValueType::AttrSet);
+        })
+        .unwrap();
+    }
+
+    #[test]
+    fn eval_state_value_list() {
+        gc_registering_current_thread(|| {
+            let store = Store::open("auto").unwrap();
+            let es = EvalState::new(store).unwrap();
+            let v = es
+                .eval_from_string("[ ]".to_string(), "<test>".to_string())
+                .unwrap();
+            es.force(&v).unwrap();
+            let t = es.value_type(&v).unwrap();
+            assert!(t == ValueType::List);
+        })
+        .unwrap();
+    }
+}

rust/nix-expr/src/lib.rs

@@ -0,0 +1,2 @@
+pub mod eval_state;
+pub mod value;

rust/nix-expr/src/value.rs

@@ -0,0 +1,75 @@
+use nix_c_raw as raw;
+use nix_util::context::Context;
+use std::ptr::NonNull;
+
+// TODO: test: cloning a thunk does not duplicate the evaluation.
+
+/** The type of a value (or thunk) */
+#[derive(Eq, PartialEq)]
+pub enum ValueType {
+    AttrSet,
+    Bool,
+    External,
+    Float,
+    Function,
+    Int,
+    List,
+    Null,
+    Path,
+    String,
+    Thunk,
+    Unknown,
+}
+
+impl ValueType {
+    pub(crate) fn from_raw(raw: raw::ValueType) -> ValueType {
+        match raw {
+            raw::ValueType_NIX_TYPE_ATTRS => ValueType::AttrSet,
+            raw::ValueType_NIX_TYPE_BOOL => ValueType::Bool,
+            raw::ValueType_NIX_TYPE_EXTERNAL => ValueType::External,
+            raw::ValueType_NIX_TYPE_FLOAT => ValueType::Float,
+            raw::ValueType_NIX_TYPE_FUNCTION => ValueType::Function,
+            raw::ValueType_NIX_TYPE_INT => ValueType::Int,
+            raw::ValueType_NIX_TYPE_LIST => ValueType::List,
+            raw::ValueType_NIX_TYPE_NULL => ValueType::Null,
+            raw::ValueType_NIX_TYPE_PATH => ValueType::Path,
+            raw::ValueType_NIX_TYPE_STRING => ValueType::String,
+            raw::ValueType_NIX_TYPE_THUNK => ValueType::Thunk,
+            _ => ValueType::Unknown,
+        }
+    }
+}
+
+/* A pointer to a value or thunk, to be used with EvalState methods. */
+pub struct Value {
+    inner: NonNull<raw::Value>,
+}
+impl Value {
+    pub(crate) fn new(inner: *mut raw::Value) -> Self {
+        Value {
+            inner: NonNull::new(inner).unwrap(),
+        }
+    }
+    pub(crate) fn raw_ptr(&self) -> *mut raw::Value {
+        self.inner.as_ptr()
+    }
+}
+impl Drop for Value {
+    fn drop(&mut self) {
+        let context = Context::new();
+        unsafe {
+            raw::nix_gc_decref(context.ptr(), self.inner.as_ptr());
+        }
+        // ignore error from context, because drop should not panic
+    }
+}
+impl Clone for Value {
+    fn clone(&self) -> Self {
+        let context = Context::new();
+        unsafe { raw::nix_gc_incref(context.ptr(), self.inner.as_ptr()) };
+        context.check_err().unwrap();
+        Value { inner: self.inner }
+    }
+}
+
+// Tested in eval_state.rs

rust/nix-store/src/store.rs

@@ -29,7 +29,7 @@ impl StoreRef {
 impl Drop for StoreRef {
     fn drop(&mut self) {
         unsafe {
-            raw::nix_store_unref(self.inner.as_ptr());
+            raw::nix_store_free(self.inner.as_ptr());
         }
     }
 }
@@ -73,6 +73,10 @@ impl Store {
         Ok(store)
     }
 
+    pub fn raw_ptr(&self) -> *mut raw::Store {
+        self.inner.ptr()
+    }
+
     pub fn get_uri(&self) -> Result<String> {
         const N: usize = 1024;
         let mut buffer: [MaybeUninit<u8>; N] = unsafe { MaybeUninit::uninit().assume_init() };