refactor(tvix/eval): Pull context out into its own module r/8515

I'm gonna be doing some poking around in the internals of Context, so in
preparation this pulls it out into its own module.

Change-Id: I72ea7df80b5f36f838934ee07bdba66874c334c9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12189
Autosubmit: aspen <root@gws.fyi>
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI

1 files changed, 0 insertions, 1031 deletions

diff --git a/tvix/eval/src/value/string.rs b/tvix/eval/src/value/string.rs
deleted file mode 100644
index 3680df3afb2d..000000000000
--- a/tvix/eval/src/value/string.rs
+++ /dev/null
@@ -1,1031 +0,0 @@
-//! This module implements Nix language strings.
-//!
-//! See [`NixString`] for more information about the internals of string values
-
-use bstr::{BStr, BString, ByteSlice, Chars};
-use nohash_hasher::BuildNoHashHasher;
-use rnix::ast;
-use rustc_hash::FxHashSet;
-use rustc_hash::FxHasher;
-use std::alloc::dealloc;
-use std::alloc::{alloc, handle_alloc_error, Layout};
-use std::borrow::{Borrow, Cow};
-use std::cell::RefCell;
-use std::ffi::c_void;
-use std::fmt::{self, Debug, Display};
-use std::hash::{Hash, Hasher};
-use std::ops::Deref;
-use std::ptr::{self, NonNull};
-use std::slice;
-
-use serde::de::{Deserializer, Visitor};
-use serde::{Deserialize, Serialize};
-
-#[derive(Clone, Debug, Serialize, Hash, PartialEq, Eq)]
-pub enum NixContextElement {
-    /// A plain store path (e.g. source files copied to the store)
-    Plain(String),
-
-    /// Single output of a derivation, represented by its name and its derivation path.
-    Single { name: String, derivation: String },
-
-    /// A reference to a complete derivation
-    /// including its source and its binary closure.
-    /// It is used for the `drvPath` attribute context.
-    /// The referred string is the store path to
-    /// the derivation path.
-    Derivation(String),
-}
-
-/// Nix context strings representation in Tvix. This tracks a set of different kinds of string
-/// dependencies that we can come across during manipulation of our language primitives, mostly
-/// strings. There's some simple algebra of context strings and how they propagate w.r.t. primitive
-/// operations, e.g. concatenation, interpolation and other string operations.
-#[repr(transparent)]
-#[derive(Clone, Debug, Serialize, Default)]
-pub struct NixContext(FxHashSet<NixContextElement>);
-
-impl From<NixContextElement> for NixContext {
-    fn from(value: NixContextElement) -> Self {
-        let mut set = FxHashSet::default();
-        set.insert(value);
-        Self(set)
-    }
-}
-
-impl From<FxHashSet<NixContextElement>> for NixContext {
-    fn from(value: FxHashSet<NixContextElement>) -> Self {
-        Self(value)
-    }
-}
-
-impl<const N: usize> From<[NixContextElement; N]> for NixContext {
-    fn from(value: [NixContextElement; N]) -> Self {
-        let mut set = FxHashSet::default();
-        for elt in value {
-            set.insert(elt);
-        }
-        Self(set)
-    }
-}
-
-impl NixContext {
-    /// Creates an empty context that can be populated
-    /// and passed to form a contextful [NixString], albeit
-    /// if the context is concretly empty, the resulting [NixString]
-    /// will be contextless.
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    /// For internal consumers, we let people observe
-    /// if the [NixContext] is actually empty or not
-    /// to decide whether they want to skip the allocation
-    /// of a full blown [HashSet].
-    pub(crate) fn is_empty(&self) -> bool {
-        self.0.is_empty()
-    }
-
-    /// Consumes a new [NixContextElement] and add it if not already
-    /// present in this context.
-    pub fn append(mut self, other: NixContextElement) -> Self {
-        self.0.insert(other);
-        self
-    }
-
-    /// Extends the existing context with more context elements.
-    pub fn extend<T>(&mut self, iter: T)
-    where
-        T: IntoIterator<Item = NixContextElement>,
-    {
-        self.0.extend(iter)
-    }
-
-    /// Copies from another [NixString] its context strings
-    /// in this context.
-    pub fn mimic(&mut self, other: &NixString) {
-        if let Some(context) = other.context() {
-            self.extend(context.iter().cloned());
-        }
-    }
-
-    /// Iterates over "plain" context elements, e.g. sources imported
-    /// in the store without more information, i.e. `toFile` or coerced imported paths.
-    /// It yields paths to the store.
-    pub fn iter_plain(&self) -> impl Iterator<Item = &str> {
-        self.iter().filter_map(|elt| {
-            if let NixContextElement::Plain(s) = elt {
-                Some(s.as_str())
-            } else {
-                None
-            }
-        })
-    }
-
-    /// Iterates over "full derivations" context elements, e.g. something
-    /// referring to their `drvPath`, i.e. their full sources and binary closure.
-    /// It yields derivation paths.
-    pub fn iter_derivation(&self) -> impl Iterator<Item = &str> {
-        self.iter().filter_map(|elt| {
-            if let NixContextElement::Derivation(s) = elt {
-                Some(s.as_str())
-            } else {
-                None
-            }
-        })
-    }
-
-    /// Iterates over "single" context elements, e.g. single derived paths,
-    /// or also known as the single output of a given derivation.
-    /// The first element of the tuple is the output name
-    /// and the second element is the derivation path.
-    pub fn iter_single_outputs(&self) -> impl Iterator<Item = (&str, &str)> {
-        self.iter().filter_map(|elt| {
-            if let NixContextElement::Single { name, derivation } = elt {
-                Some((name.as_str(), derivation.as_str()))
-            } else {
-                None
-            }
-        })
-    }
-
-    /// Iterates over any element of the context.
-    pub fn iter(&self) -> impl Iterator<Item = &NixContextElement> {
-        self.0.iter()
-    }
-
-    /// Produces a list of owned references to this current context,
-    /// no matter its type.
-    pub fn to_owned_references(self) -> Vec<String> {
-        self.0
-            .into_iter()
-            .map(|ctx| match ctx {
-                NixContextElement::Derivation(drv_path) => drv_path,
-                NixContextElement::Plain(store_path) => store_path,
-                NixContextElement::Single { derivation, .. } => derivation,
-            })
-            .collect()
-    }
-}
-
-impl IntoIterator for NixContext {
-    type Item = NixContextElement;
-
-    type IntoIter = std::collections::hash_set::IntoIter<NixContextElement>;
-
-    fn into_iter(self) -> Self::IntoIter {
-        self.0.into_iter()
-    }
-}
-
-/// This type is never instantiated, but serves to document the memory layout of the actual heap
-/// allocation for Nix strings.
-#[allow(dead_code)]
-struct NixStringInner {
-    /// The string context, if any.  Note that this is boxed to take advantage of the null pointer
-    /// niche, otherwise this field ends up being very large:
-    ///
-    /// ```notrust
-    /// >> std::mem::size_of::<Option<HashSet<String>>>()
-    /// 48
-    ///
-    /// >> std::mem::size_of::<Option<Box<HashSet<String>>>>()
-    /// 8
-    /// ```
-    context: Option<Box<NixContext>>,
-    /// The length of the data, stored *inline in the allocation*
-    length: usize,
-    /// The actual data for the string itself. Will always be `length` bytes long
-    data: [u8],
-}
-
-#[allow(clippy::zst_offset)]
-impl NixStringInner {
-    /// Construct a [`Layout`] for a nix string allocation with the given length.
-    ///
-    /// Returns a tuple of:
-    /// 1. The layout itself.
-    /// 2. The offset of [`Self::length`] within the allocation, assuming the allocation starts at 0
-    /// 3. The offset of the data array within the allocation, assuming the allocation starts at 0
-    fn layout(len: usize) -> (Layout, usize, usize) {
-        let layout = Layout::new::<Option<Box<NixContext>>>();
-        let (layout, len_offset) = layout.extend(Layout::new::<usize>()).unwrap();
-        let (layout, data_offset) = layout.extend(Layout::array::<u8>(len).unwrap()).unwrap();
-        (layout, len_offset, data_offset)
-    }
-
-    /// Returns the [`Layout`] for an *already-allocated* nix string, loading the length from the
-    /// pointer.
-    ///
-    /// Returns a tuple of:
-    /// 1. The layout itself.
-    /// 2. The offset of [`Self::length`] within the allocation, assuming the allocation starts at 0
-    /// 3. The offset of the data array within the allocation, assuming the allocation starts at 0
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called on a pointer that has been properly initialized with
-    /// [`Self::alloc`]. The data buffer may not necessarily be initialized
-    unsafe fn layout_of(this: NonNull<c_void>) -> (Layout, usize, usize) {
-        let layout = Layout::new::<Option<Box<NixContext>>>();
-        let (_, len_offset) = layout.extend(Layout::new::<usize>()).unwrap();
-        // SAFETY: Layouts are linear, so even though we haven't involved data at all yet, we know
-        // the len_offset is a valid offset into the second field of the allocation
-        let len = *(this.as_ptr().add(len_offset) as *const usize);
-        Self::layout(len)
-    }
-
-    /// Allocate an *uninitialized* nix string with the given length. Writes the length to the
-    /// length value in the pointer, but leaves both context and data uninitialized
-    ///
-    /// This function is safe to call (as constructing pointers of any sort of validity is always
-    /// safe in Rust) but it is unsafe to use the resulting pointer to do anything other than
-    ///
-    /// 1. Read the length
-    /// 2. Write the context
-    /// 3. Write the data
-    ///
-    /// until the string is fully initialized
-    fn alloc(len: usize) -> NonNull<c_void> {
-        let (layout, len_offset, _data_offset) = Self::layout(len);
-        debug_assert_ne!(layout.size(), 0);
-        unsafe {
-            // SAFETY: Layout has non-zero size, since the layout of the context and the
-            // layout of the len both have non-zero size
-            let ptr = alloc(layout);
-
-            if let Some(this) = NonNull::new(ptr as *mut _) {
-                // SAFETY: We've allocated with a layout that causes the len_offset to be in-bounds
-                // and writeable, and if the allocation succeeded it won't wrap
-                ((this.as_ptr() as *mut u8).add(len_offset) as *mut usize).write(len);
-                debug_assert_eq!(Self::len(this), len);
-                this
-            } else {
-                handle_alloc_error(layout);
-            }
-        }
-    }
-
-    /// Deallocate the Nix string at the given pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`]
-    unsafe fn dealloc(this: NonNull<c_void>) {
-        let (layout, _, _) = Self::layout_of(this);
-        // SAFETY: okay because of the safety guarantees of this method
-        dealloc(this.as_ptr() as *mut u8, layout)
-    }
-
-    /// Return the length of the Nix string at the given pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`]
-    unsafe fn len(this: NonNull<c_void>) -> usize {
-        let (_, len_offset, _) = Self::layout_of(this);
-        // SAFETY: As long as the safety guarantees of this method are upheld, we've allocated with
-        // a layout that causes the len_offset to be in-bounds and writeable, and if the allocation
-        // succeeded it won't wrap
-        *(this.as_ptr().add(len_offset) as *const usize)
-    }
-
-    /// Return a pointer to the context value within the given Nix string pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`]
-    unsafe fn context_ptr(this: NonNull<c_void>) -> *mut Option<Box<NixContext>> {
-        // SAFETY: The context is the first field in the layout of the allocation
-        this.as_ptr() as *mut Option<Box<NixContext>>
-    }
-
-    /// Construct a shared reference to the context value within the given Nix string pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`], and where the context has been properly initialized (by writing to the
-    /// pointer returned from [`Self::context_ptr`]).
-    ///
-    /// Also, all the normal Rust rules about pointer-to-reference conversion apply. See
-    /// [`NonNull::as_ref`] for more.
-    unsafe fn context_ref<'a>(this: NonNull<c_void>) -> &'a Option<Box<NixContext>> {
-        Self::context_ptr(this).as_ref().unwrap()
-    }
-
-    /// Construct a mutable reference to the context value within the given Nix string pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`], and where the context has been properly initialized (by writing to the
-    /// pointer returned from [`Self::context_ptr`]).
-    ///
-    /// Also, all the normal Rust rules about pointer-to-reference conversion apply. See
-    /// [`NonNull::as_mut`] for more.
-    unsafe fn context_mut<'a>(this: NonNull<c_void>) -> &'a mut Option<Box<NixContext>> {
-        Self::context_ptr(this).as_mut().unwrap()
-    }
-
-    /// Return a pointer to the data array within the given Nix string pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`]
-    unsafe fn data_ptr(this: NonNull<c_void>) -> *mut u8 {
-        let (_, _, data_offset) = Self::layout_of(this);
-        // SAFETY: data is the third field in the layout of the allocation
-        this.as_ptr().add(data_offset) as *mut u8
-    }
-
-    /// Construct a shared reference to the data slice within the given Nix string pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`], and where the data array has been properly initialized (by writing to the
-    /// pointer returned from [`Self::data_ptr`]).
-    ///
-    /// Also, all the normal Rust rules about pointer-to-reference conversion apply. See
-    /// [`slice::from_raw_parts`] for more.
-    unsafe fn data_slice<'a>(this: NonNull<c_void>) -> &'a [u8] {
-        let len = Self::len(this);
-        let data = Self::data_ptr(this);
-        slice::from_raw_parts(data, len)
-    }
-
-    /// Construct a mutable reference to the data slice within the given Nix string pointer
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`], and where the data array has been properly initialized (by writing to the
-    /// pointer returned from [`Self::data_ptr`]).
-    ///
-    /// Also, all the normal Rust rules about pointer-to-reference conversion apply. See
-    /// [`slice::from_raw_parts_mut`] for more.
-    #[allow(dead_code)]
-    unsafe fn data_slice_mut<'a>(this: NonNull<c_void>) -> &'a mut [u8] {
-        let len = Self::len(this);
-        let data = Self::data_ptr(this);
-        slice::from_raw_parts_mut(data, len)
-    }
-
-    /// Clone the Nix string pointed to by this pointer, and return a pointer to a new Nix string
-    /// containing the same data and context.
-    ///
-    /// # Safety
-    ///
-    /// This function must only be called with a pointer that has been properly initialized with
-    /// [`Self::alloc`], and where the context has been properly initialized (by writing to the
-    /// pointer returned from [`Self::context_ptr`]), and the data array has been properly
-    /// initialized (by writing to the pointer returned from [`Self::data_ptr`]).
-    unsafe fn clone(this: NonNull<c_void>) -> NonNull<c_void> {
-        let (layout, _, _) = Self::layout_of(this);
-        let ptr = alloc(layout);
-        if let Some(new) = NonNull::new(ptr as *mut _) {
-            ptr::copy_nonoverlapping(this.as_ptr(), new.as_ptr(), layout.size());
-            Self::context_ptr(new).write(Self::context_ref(this).clone());
-            new
-        } else {
-            handle_alloc_error(layout);
-        }
-    }
-}
-
-#[derive(Default)]
-struct InternerInner {
-    #[allow(clippy::disallowed_types)] // Not using the default hasher
-    map: std::collections::HashMap<u64, NonNull<c_void>, BuildNoHashHasher<u64>>,
-    #[cfg(feature = "no_leak")]
-    #[allow(clippy::disallowed_types)] // Not using the default hasher
-    interned_strings: FxHashSet<NonNull<c_void>>,
-}
-
-unsafe impl Send for InternerInner {}
-
-fn hash<T>(s: T) -> u64
-where
-    T: Hash,
-{
-    let mut hasher = FxHasher::default();
-    s.hash(&mut hasher);
-    hasher.finish()
-}
-
-impl InternerInner {
-    pub fn intern(&mut self, s: &[u8]) -> NixString {
-        let hash = hash(s);
-        if let Some(s) = self.map.get(&hash) {
-            return NixString(*s);
-        }
-
-        let string = NixString::new_inner(s, None);
-        self.map.insert(hash, string.0);
-        #[cfg(feature = "no_leak")]
-        self.interned_strings.insert(string.0);
-        string
-    }
-}
-
-#[derive(Default)]
-struct Interner(RefCell<InternerInner>);
-
-impl Interner {
-    pub fn intern(&self, s: &[u8]) -> NixString {
-        self.0.borrow_mut().intern(s)
-    }
-
-    #[cfg(feature = "no_leak")]
-    pub fn is_interned_string(&self, string: &NixString) -> bool {
-        self.0.borrow().interned_strings.contains(&string.0)
-    }
-}
-
-thread_local! {
-    static INTERNER: Interner = Interner::default();
-}
-
-/// Nix string values
-///
-/// # Internals
-///
-/// For performance reasons (to keep allocations small, and to avoid indirections), [`NixString`] is
-/// represented as a single *thin* pointer to a packed data structure containing the
-/// [context][NixContext] and the string data itself (which is a raw byte array, to match the Nix
-/// string semantics that allow any array of bytes to be represented by a string).
-
-/// This memory representation is documented in [`NixStringInner`], but since Rust prefers to deal
-/// with slices via *fat pointers* (pointers that include the length in the *pointer*, not in the
-/// heap allocation), we have to do mostly manual layout management and allocation for this
-/// representation. See the documentation for the methods of [`NixStringInner`] for more information
-pub struct NixString(NonNull<c_void>);
-
-unsafe impl Send for NixString {}
-unsafe impl Sync for NixString {}
-
-impl Drop for NixString {
-    #[cfg(not(feature = "no_leak"))]
-    fn drop(&mut self) {
-        if self.context().is_some() {
-            // SAFETY: There's no way to construct a NixString that doesn't leave the allocation correct
-            // according to the rules of dealloc
-            unsafe {
-                NixStringInner::dealloc(self.0);
-            }
-        }
-    }
-
-    #[cfg(feature = "no_leak")]
-    fn drop(&mut self) {
-        if INTERNER.with(|i| i.is_interned_string(self)) {
-            return;
-        }
-
-        // SAFETY: There's no way to construct a NixString that doesn't leave the allocation correct
-        // according to the rules of dealloc
-        unsafe {
-            NixStringInner::dealloc(self.0);
-        }
-    }
-}
-
-impl Clone for NixString {
-    fn clone(&self) -> Self {
-        if cfg!(feature = "no_leak") || self.context().is_some() {
-            // SAFETY: There's no way to construct a NixString that doesn't leave the allocation correct
-            // according to the rules of clone
-            unsafe { Self(NixStringInner::clone(self.0)) }
-        } else {
-            // SAFETY:
-            //
-            // - NixStrings are never mutated
-            // - NixStrings are never freed
-            Self(self.0)
-        }
-    }
-}
-
-impl Debug for NixString {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        if let Some(ctx) = self.context() {
-            f.debug_struct("NixString")
-                .field("context", ctx)
-                .field("data", &self.as_bstr())
-                .finish()
-        } else {
-            write!(f, "{:?}", self.as_bstr())
-        }
-    }
-}
-
-impl PartialEq for NixString {
-    fn eq(&self, other: &Self) -> bool {
-        self.0 == other.0 || self.as_bstr() == other.as_bstr()
-    }
-}
-
-impl Eq for NixString {}
-
-impl PartialEq<&[u8]> for NixString {
-    fn eq(&self, other: &&[u8]) -> bool {
-        **self == **other
-    }
-}
-
-impl PartialEq<&str> for NixString {
-    fn eq(&self, other: &&str) -> bool {
-        **self == other.as_bytes()
-    }
-}
-
-impl PartialOrd for NixString {
-    fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
-        Some(self.cmp(other))
-    }
-}
-
-impl Ord for NixString {
-    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-        if self.0 == other.0 {
-            return std::cmp::Ordering::Equal;
-        }
-        self.as_bstr().cmp(other.as_bstr())
-    }
-}
-
-impl From<Box<BStr>> for NixString {
-    fn from(value: Box<BStr>) -> Self {
-        Self::new(&value, None)
-    }
-}
-
-impl From<BString> for NixString {
-    fn from(value: BString) -> Self {
-        Self::new(&value, None)
-    }
-}
-
-impl From<&BStr> for NixString {
-    fn from(value: &BStr) -> Self {
-        value.to_owned().into()
-    }
-}
-
-impl From<&[u8]> for NixString {
-    fn from(value: &[u8]) -> Self {
-        Self::from(value.to_owned())
-    }
-}
-
-impl From<Vec<u8>> for NixString {
-    fn from(value: Vec<u8>) -> Self {
-        value.into_boxed_slice().into()
-    }
-}
-
-impl From<Box<[u8]>> for NixString {
-    fn from(value: Box<[u8]>) -> Self {
-        Self::new(&value, None)
-    }
-}
-
-impl From<&str> for NixString {
-    fn from(s: &str) -> Self {
-        s.as_bytes().into()
-    }
-}
-
-impl From<String> for NixString {
-    fn from(s: String) -> Self {
-        s.into_bytes().into()
-    }
-}
-
-impl<T> From<(T, Option<Box<NixContext>>)> for NixString
-where
-    NixString: From<T>,
-{
-    fn from((s, ctx): (T, Option<Box<NixContext>>)) -> Self {
-        Self::new(NixString::from(s).as_ref(), ctx)
-    }
-}
-
-impl From<Box<str>> for NixString {
-    fn from(s: Box<str>) -> Self {
-        s.into_boxed_bytes().into()
-    }
-}
-
-impl From<ast::Ident> for NixString {
-    fn from(ident: ast::Ident) -> Self {
-        ident.ident_token().unwrap().text().into()
-    }
-}
-
-impl<'a> From<&'a NixString> for &'a BStr {
-    fn from(s: &'a NixString) -> Self {
-        s.as_bstr()
-    }
-}
-
-// No impl From<NixString> for String, that one quotes.
-
-impl From<NixString> for BString {
-    fn from(s: NixString) -> Self {
-        s.as_bstr().to_owned()
-    }
-}
-
-impl AsRef<[u8]> for NixString {
-    fn as_ref(&self) -> &[u8] {
-        self.as_bytes()
-    }
-}
-
-impl Borrow<BStr> for NixString {
-    fn borrow(&self) -> &BStr {
-        self.as_bstr()
-    }
-}
-
-impl Hash for NixString {
-    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
-        self.as_bstr().hash(state)
-    }
-}
-
-impl<'de> Deserialize<'de> for NixString {
-    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
-    where
-        D: Deserializer<'de>,
-    {
-        struct StringVisitor;
-
-        impl<'de> Visitor<'de> for StringVisitor {
-            type Value = NixString;
-
-            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
-                formatter.write_str("a valid Nix string")
-            }
-
-            fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
-            where
-                E: serde::de::Error,
-            {
-                Ok(v.into())
-            }
-
-            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
-            where
-                E: serde::de::Error,
-            {
-                Ok(v.into())
-            }
-        }
-
-        deserializer.deserialize_string(StringVisitor)
-    }
-}
-
-impl Deref for NixString {
-    type Target = BStr;
-
-    fn deref(&self) -> &Self::Target {
-        self.as_bstr()
-    }
-}
-
-#[cfg(feature = "arbitrary")]
-mod arbitrary {
-    use super::*;
-    use proptest::prelude::{any_with, Arbitrary};
-    use proptest::strategy::{BoxedStrategy, Strategy};
-
-    impl Arbitrary for NixString {
-        type Parameters = <String as Arbitrary>::Parameters;
-
-        type Strategy = BoxedStrategy<Self>;
-
-        fn arbitrary_with(args: Self::Parameters) -> Self::Strategy {
-            any_with::<String>(args).prop_map(Self::from).boxed()
-        }
-    }
-}
-
-/// Set non-scientifically. TODO(aspen): think more about what this should be
-const INTERN_THRESHOLD: usize = 32;
-
-impl NixString {
-    fn new(contents: &[u8], context: Option<Box<NixContext>>) -> Self {
-        debug_assert!(
-            !context.as_deref().is_some_and(NixContext::is_empty),
-            "BUG: initialized with empty context"
-        );
-
-        if !cfg!(feature = "no_leak") /* It's only safe to intern if we leak strings, since there's
-                                       * nothing yet preventing interned strings from getting freed
-                                       * (and then used by other copies) otherwise
-                                       */
-            && contents.len() <= INTERN_THRESHOLD
-            && context.is_none()
-        {
-            return INTERNER.with(|i| i.intern(contents));
-        }
-
-        Self::new_inner(contents, context)
-    }
-
-    fn new_inner(contents: &[u8], context: Option<Box<NixContext>>) -> Self {
-        // SAFETY: We're always fully initializing a NixString here:
-        //
-        // 1. NixStringInner::alloc sets up the len for us
-        // 2. We set the context, using ptr::write to make sure that the uninitialized memory isn't
-        //    read or dropped
-        // 3. We set the data, using copy_from_nonoverlapping to make sure that the uninitialized
-        //    memory isn't read or dropped
-        //
-        // Only *then* can we construct a NixString
-        unsafe {
-            let inner = NixStringInner::alloc(contents.len());
-            NixStringInner::context_ptr(inner).write(context);
-            NixStringInner::data_ptr(inner)
-                .copy_from_nonoverlapping(contents.as_ptr(), contents.len());
-            Self(inner)
-        }
-    }
-
-    pub fn new_inherit_context_from<T>(other: &NixString, new_contents: T) -> Self
-    where
-        NixString: From<T>,
-    {
-        Self::new(
-            Self::from(new_contents).as_ref(),
-            other.context().map(|c| Box::new(c.clone())),
-        )
-    }
-
-    pub fn new_context_from<T>(context: NixContext, contents: T) -> Self
-    where
-        NixString: From<T>,
-    {
-        Self::new(
-            Self::from(contents).as_ref(),
-            if context.is_empty() {
-                None
-            } else {
-                Some(Box::new(context))
-            },
-        )
-    }
-
-    pub fn as_bstr(&self) -> &BStr {
-        BStr::new(self.as_bytes())
-    }
-
-    pub fn as_bytes(&self) -> &[u8] {
-        // SAFETY: There's no way to construct an uninitialized NixString (see the SAFETY comment in
-        // `new`)
-        unsafe { NixStringInner::data_slice(self.0) }
-    }
-
-    pub fn into_bstring(self) -> BString {
-        self.as_bstr().to_owned()
-    }
-
-    /// Return a displayable representation of the string as an
-    /// identifier.
-    ///
-    /// This is used when printing out strings used as e.g. attribute
-    /// set keys, as those are only escaped in the presence of special
-    /// characters.
-    pub fn ident_str(&self) -> Cow<str> {
-        let escaped = match self.to_str_lossy() {
-            Cow::Borrowed(s) => nix_escape_string(s),
-            Cow::Owned(s) => nix_escape_string(&s).into_owned().into(),
-        };
-        match escaped {
-            // A borrowed string is unchanged and can be returned as
-            // is.
-            Cow::Borrowed(_) => {
-                if is_valid_nix_identifier(&escaped) && !is_keyword(&escaped) {
-                    escaped
-                } else {
-                    Cow::Owned(format!("\"{}\"", escaped))
-                }
-            }
-
-            // An owned string has escapes, and needs the outer quotes
-            // for display.
-            Cow::Owned(s) => Cow::Owned(format!("\"{}\"", s)),
-        }
-    }
-
-    pub fn concat(&self, other: &Self) -> Self {
-        let mut s = self.to_vec();
-        s.extend(&(***other));
-
-        let context = [self.context(), other.context()]
-            .into_iter()
-            .flatten()
-            .fold(NixContext::new(), |mut acc_ctx, new_ctx| {
-                // TODO: consume new_ctx?
-                acc_ctx.extend(new_ctx.iter().cloned());
-                acc_ctx
-            });
-        Self::new_context_from(context, s)
-    }
-
-    pub(crate) fn context(&self) -> Option<&NixContext> {
-        // SAFETY: There's no way to construct an uninitialized or invalid NixString (see the SAFETY
-        // comment in `new`).
-        //
-        // Also, we're using the same lifetime and mutability as self, to fit the
-        // pointer-to-reference conversion rules
-        let context = unsafe { NixStringInner::context_ref(self.0).as_deref() };
-
-        debug_assert!(
-            !context.is_some_and(NixContext::is_empty),
-            "BUG: empty context"
-        );
-
-        context
-    }
-
-    pub(crate) fn context_mut(&mut self) -> &mut Option<Box<NixContext>> {
-        // SAFETY: There's no way to construct an uninitialized or invalid NixString (see the SAFETY
-        // comment in `new`).
-        //
-        // Also, we're using the same lifetime and mutability as self, to fit the
-        // pointer-to-reference conversion rules
-        let context = unsafe { NixStringInner::context_mut(self.0) };
-
-        debug_assert!(
-            !context.as_deref().is_some_and(NixContext::is_empty),
-            "BUG: empty context"
-        );
-
-        context
-    }
-
-    /// Iterates over all context elements.
-    /// See [iter_plain], [iter_derivation], [iter_single_outputs].
-    pub fn iter_context(&self) -> impl Iterator<Item = &NixContext> {
-        self.context().into_iter()
-    }
-
-    /// Iterates over "plain" context elements, e.g. sources imported
-    /// in the store without more information, i.e. `toFile` or coerced imported paths.
-    /// It yields paths to the store.
-    pub fn iter_ctx_plain(&self) -> impl Iterator<Item = &str> {
-        self.iter_context().flat_map(|context| context.iter_plain())
-    }
-
-    /// Iterates over "full derivations" context elements, e.g. something
-    /// referring to their `drvPath`, i.e. their full sources and binary closure.
-    /// It yields derivation paths.
-    pub fn iter_ctx_derivation(&self) -> impl Iterator<Item = &str> {
-        return self
-            .iter_context()
-            .flat_map(|context| context.iter_derivation());
-    }
-
-    /// Iterates over "single" context elements, e.g. single derived paths,
-    /// or also known as the single output of a given derivation.
-    /// The first element of the tuple is the output name
-    /// and the second element is the derivation path.
-    pub fn iter_ctx_single_outputs(&self) -> impl Iterator<Item = (&str, &str)> {
-        return self
-            .iter_context()
-            .flat_map(|context| context.iter_single_outputs());
-    }
-
-    /// Returns whether this Nix string possess a context or not.
-    pub fn has_context(&self) -> bool {
-        self.context().is_some()
-    }
-
-    /// This clears the context of the string, returning
-    /// the removed dependency tracking information.
-    pub fn take_context(&mut self) -> Option<Box<NixContext>> {
-        self.context_mut().take()
-    }
-
-    /// This clears the context of that string, losing
-    /// all dependency tracking information.
-    pub fn clear_context(&mut self) {
-        let _ = self.take_context();
-    }
-
-    pub fn chars(&self) -> Chars<'_> {
-        self.as_bstr().chars()
-    }
-}
-
-fn nix_escape_char(ch: char, next: Option<&char>) -> Option<&'static str> {
-    match (ch, next) {
-        ('\\', _) => Some("\\\\"),
-        ('"', _) => Some("\\\""),
-        ('\n', _) => Some("\\n"),
-        ('\t', _) => Some("\\t"),
-        ('\r', _) => Some("\\r"),
-        ('$', Some('{')) => Some("\\$"),
-        _ => None,
-    }
-}
-
-/// Return true if this string is a keyword -- character strings
-/// which lexically match the "identifier" production but are not
-/// parsed as identifiers.  See also cppnix commit
-/// b72bc4a972fe568744d98b89d63adcd504cb586c.
-fn is_keyword(s: &str) -> bool {
-    matches!(
-        s,
-        "if" | "then" | "else" | "assert" | "with" | "let" | "in" | "rec" | "inherit"
-    )
-}
-
-/// Return true if this string can be used as an identifier in Nix.
-fn is_valid_nix_identifier(s: &str) -> bool {
-    // adapted from rnix-parser's tokenizer.rs
-    let mut chars = s.chars();
-    match chars.next() {
-        Some('a'..='z' | 'A'..='Z' | '_') => (),
-        _ => return false,
-    }
-    for c in chars {
-        match c {
-            'a'..='z' | 'A'..='Z' | '0'..='9' | '_' | '-' | '\'' => (),
-            _ => return false,
-        }
-    }
-    true
-}
-
-/// Escape a Nix string for display, as most user-visible representation
-/// are escaped strings.
-///
-/// Note that this does not add the outer pair of surrounding quotes.
-fn nix_escape_string(input: &str) -> Cow<str> {
-    let mut iter = input.char_indices().peekable();
-
-    while let Some((i, c)) = iter.next() {
-        if let Some(esc) = nix_escape_char(c, iter.peek().map(|(_, c)| c)) {
-            let mut escaped = String::with_capacity(input.len());
-            escaped.push_str(&input[..i]);
-            escaped.push_str(esc);
-
-            // In theory we calculate how many bytes it takes to represent `esc`
-            // in UTF-8 and use that for the offset. It is, however, safe to
-            // assume that to be 1, as all characters that can be escaped in a
-            // Nix string are ASCII.
-            let mut inner_iter = input[i + 1..].chars().peekable();
-            while let Some(c) = inner_iter.next() {
-                match nix_escape_char(c, inner_iter.peek()) {
-                    Some(esc) => escaped.push_str(esc),
-                    None => escaped.push(c),
-                }
-            }
-
-            return Cow::Owned(escaped);
-        }
-    }
-
-    Cow::Borrowed(input)
-}
-
-impl Display for NixString {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        f.write_str("\"")?;
-        f.write_str(&nix_escape_string(&self.to_str_lossy()))?;
-        f.write_str("\"")
-    }
-}
-
-#[cfg(all(test, feature = "arbitrary"))]
-mod tests {
-    use test_strategy::proptest;
-
-    use super::*;
-
-    use crate::properties::{eq_laws, hash_laws, ord_laws};
-
-    #[test]
-    fn size() {
-        assert_eq!(std::mem::size_of::<NixString>(), 8);
-    }
-
-    #[proptest]
-    fn clone_strings(s: NixString) {
-        drop(s.clone())
-    }
-
-    eq_laws!(NixString);
-    hash_laws!(NixString);
-    ord_laws!(NixString);
-}