nixide/rust/nix-expr/src/eval_state.rs

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::path::StorePath;
use nix_store::store::Store;
use nix_util::context::Context;
use nix_util::result_string_init;
use nix_util::string_return::{callback_get_result_string, callback_get_result_string_data};
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::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 RealisedString {
    pub s: String,
    pub paths: Vec<StorePath>,
}

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::state_create(
                context.ptr(),
                /* searchPath */ null_mut(),
                store.raw_ptr(),
            )
        };
        context.check_err()?;
        if eval_state.is_null() {
            panic!("nix_state_create returned a null pointer without an error");
        }
        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: &str, path: &str) -> 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::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::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::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::get_type(self.context.ptr(), value.raw_ptr()) };
        Ok(ValueType::from_raw(r))
    }
    /// Not exposed, because the caller must always explicitly handle the context or not accept one at all.
    fn get_string(&self, value: &Value) -> Result<String> {
        let mut r = result_string_init!();
        unsafe {
            raw::get_string(
                self.context.ptr(),
                value.raw_ptr(),
                Some(callback_get_result_string),
                callback_get_result_string_data(&mut r),
            )
        };
        self.context.check_err()?;
        r
    }
    /// NOTE: this will be replaced by two methods, one that also returns the context, and one that checks that the context is empty
    pub fn require_string(&self, value: &Value) -> Result<String> {
        let t = self.value_type(value)?;
        if t != ValueType::String {
            bail!("expected a string, but got a {:?}", t);
        }
        self.get_string(value)
    }
    pub fn realise_string(
        &self,
        value: &Value,
        is_import_from_derivation: bool,
    ) -> Result<RealisedString> {
        let t = self.value_type(value)?;
        if t != ValueType::String {
            bail!("expected a string, but got a {:?}", t);
        }

        let rs = unsafe {
            raw::string_realise(
                self.context.ptr(),
                self.raw_ptr(),
                value.raw_ptr(),
                is_import_from_derivation,
            )
        };
        self.context.check_err()?;

        let s = unsafe {
            let start = raw::realised_string_get_buffer_start(rs) as *const u8;
            let size = raw::realised_string_get_buffer_size(rs);
            let slice = std::slice::from_raw_parts(start, size);
            String::from_utf8(slice.to_vec())
                .map_err(|e| anyhow::format_err!("Nix string is not valid UTF-8: {}", e))?
        };

        let paths = unsafe {
            let n = raw::realised_string_get_store_path_count(rs);
            let mut paths = Vec::with_capacity(n as usize);
            for i in 0..n {
                let path = raw::realised_string_get_store_path(rs, i);
                paths.push(StorePath::new_raw_clone(path));
            }
            paths
        };

        // We've converted the nix_realised_string to a native struct containing copies, so we can free it now.
        unsafe {
            raw::realised_string_free(rs);
        }

        Ok(RealisedString { s, paths })
    }

    fn new_value_uninitialized(&self) -> Value {
        let value = unsafe { raw::alloc_value(self.context.ptr(), self.raw_ptr()) };
        Value::new(value)
    }
}

pub fn gc_now() {
    unsafe {
        raw::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()?;
        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: null_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::state_free(self.raw_ptr());
        }
    }
}

#[cfg(test)]
mod tests {
    use ctor::ctor;
    use nix_util::settings;

    use super::*;

    #[ctor]
    fn setup() {
        init().unwrap();

        // During development, we encountered a problem where the build hook
        // would cause the test suite to reinvokes itself, causing an infinite loop.
        // While _NIX_TEST_NO_SANDBOX=1 should prevent this, we may also set the
        // build hook to "" to prevent this.
        // settings::set("build-hook", "")?;

        // When testing in the sandbox, the default build dir would be a parent of the storeDir,
        // which causes an error. So we set a custom build dir here.
        settings::set("sandbox-build-dir", "/custom-build-dir-for-test").unwrap();
        std::env::set_var("_NIX_TEST_NO_SANDBOX", "1");
    }

    #[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", "<test>").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", "<test>").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\"", "<test>").unwrap();
            es.force(&v).unwrap();
            let t = es.value_type(&v).unwrap();
            assert!(t == ValueType::String);
            let s = es.require_string(&v).unwrap();
            assert!(s == "hello");
        })
        .unwrap();
    }

    #[test]
    fn eval_state_value_string_unexpected_bool() {
        gc_registering_current_thread(|| {
            let store = Store::open("auto").unwrap();
            let es = EvalState::new(store).unwrap();
            let v = es.eval_from_string("true", "<test>").unwrap();
            es.force(&v).unwrap();
            let r = es.require_string(&v);
            assert!(r.is_err());
            // TODO: safe print value (like Nix would)
            assert_eq!(
                r.unwrap_err().to_string(),
                "expected a string, but got a Bool"
            );
        })
        .unwrap()
    }

    #[test]
    fn eval_state_value_string_unexpected_path_value() {
        gc_registering_current_thread(|| {
            let store = Store::open("auto").unwrap();
            let es = EvalState::new(store).unwrap();
            let v = es.eval_from_string("/foo", "<test>").unwrap();
            es.force(&v).unwrap();
            let r = es.require_string(&v);
            assert!(r.is_err());
            assert_eq!(
                r.unwrap_err().to_string(),
                "expected a string, but got a Path"
            );
        })
        .unwrap()
    }

    #[test]
    fn eval_state_value_string_bad_utf() {
        gc_registering_current_thread(|| {
            let store = Store::open("auto").unwrap();
            let es = EvalState::new(store).unwrap();
            let v = es
                .eval_from_string("builtins.substring 0 1 \"ü\"", "<test>")
                .unwrap();
            es.force(&v).unwrap();
            let t = es.value_type(&v).unwrap();
            assert!(t == ValueType::String);
            let r = es.require_string(&v);
            assert!(r.is_err());
            assert!(r
                .unwrap_err()
                .to_string()
                .contains("Nix string is not valid UTF-8"));
        })
        .unwrap();
    }

    #[test]
    fn eval_state_value_string_unexpected_context() {
        gc_registering_current_thread(|| {
            let store = Store::open("auto").unwrap();
            let es = EvalState::new(store).unwrap();
            let v = es
                .eval_from_string("(derivation { name = \"hello\"; system = \"dummy\"; builder = \"cmd.exe\"; }).outPath", "<test>")
                .unwrap();
            es.force(&v).unwrap();
            let t = es.value_type(&v).unwrap();
            assert!(t == ValueType::String);
            // TODO
            // let r = es.require_string_without_context(&v);
            // assert!(r.is_err());
            // assert!(r.unwrap_err().to_string().contains("unexpected context"));
        })
        .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("{ }", "<test>").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("[ ]", "<test>")
                .unwrap();
            es.force(&v).unwrap();
            let t = es.value_type(&v).unwrap();
            assert!(t == ValueType::List);
        })
        .unwrap();
    }

    #[test]
    fn eval_state_realise_string() {
        gc_registering_current_thread(|| {
            let store = Store::open("auto").unwrap();
            let es = EvalState::new(store).unwrap();
            let expr = r#"
                ''
                    a derivation output: ${
                        derivation { name = "letsbuild";
                            system = builtins.currentSystem;
                            builder = "/bin/sh";
                            args = [ "-c" "echo foo > $out" ];
                            }}
                    a path: ${builtins.toFile "just-a-file" "ooh file good"}
                    a derivation path by itself: ${
                        builtins.unsafeDiscardOutputDependency 
                            (derivation {
                                name = "not-actually-built-yet";
                                system = builtins.currentSystem;
                                builder = "/bin/sh";
                                args = [ "-c" "echo foo > $out" ];
                            }).drvPath}
                ''
            "#;
            let v = es.eval_from_string(expr, "<test>").unwrap();
            es.force(&v).unwrap();
            let rs = es.realise_string(&v, false).unwrap();

            assert!(rs.s.starts_with("a derivation output:"));
            assert!(rs.s.contains("-letsbuild\n"));
            assert!(!rs.s.contains("-letsbuild.drv"));
            assert!(rs.s.contains("a path:"));
            assert!(rs.s.contains("-just-a-file"));
            assert!(!rs.s.contains("-just-a-file.drv"));
            assert!(!rs.s.contains("ooh file good"));
            assert!(rs.s.ends_with("-not-actually-built-yet.drv\n"));

            assert_eq!(rs.paths.len(), 3);
            let mut names: Vec<String> = rs.paths.iter().map(|p| p.name().unwrap()).collect();
            names.sort();
            assert_eq!(names[0], "just-a-file");
            assert_eq!(names[1], "letsbuild");
            assert_eq!(names[2], "not-actually-built-yet.drv");
        })
        .unwrap();
    }
}