From 5382cbb93a94a8e68ddd2567f382661fd0f166b3 Mon Sep 17 00:00:00 2001 From: Aspen Smith Date: Sat, 10 Aug 2024 13:03:09 -0400 Subject: refactor(tvix/eval): Pull context out into its own module 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 Reviewed-by: flokli Tested-by: BuildkiteCI --- tvix/eval/src/value/string/context.rs | 161 +++++++ tvix/eval/src/value/string/mod.rs | 879 ++++++++++++++++++++++++++++++++++ 2 files changed, 1040 insertions(+) create mode 100644 tvix/eval/src/value/string/context.rs create mode 100644 tvix/eval/src/value/string/mod.rs (limited to 'tvix/eval/src/value/string') diff --git a/tvix/eval/src/value/string/context.rs b/tvix/eval/src/value/string/context.rs new file mode 100644 index 000000000000..e1c04735ddde --- /dev/null +++ b/tvix/eval/src/value/string/context.rs @@ -0,0 +1,161 @@ +use rustc_hash::FxHashSet; +use serde::Serialize; + +use super::NixString; + +#[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); + +impl From for NixContext { + fn from(value: NixContextElement) -> Self { + let mut set = FxHashSet::default(); + set.insert(value); + Self(set) + } +} + +impl From> for NixContext { + fn from(value: FxHashSet) -> Self { + Self(value) + } +} + +impl 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(&mut self, iter: T) + where + T: IntoIterator, + { + 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 { + 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 { + 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 { + 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 { + self.0.iter() + } + + /// Produces a list of owned references to this current context, + /// no matter its type. + pub fn to_owned_references(self) -> Vec { + 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; + + fn into_iter(self) -> Self::IntoIter { + self.0.into_iter() + } +} diff --git a/tvix/eval/src/value/string/mod.rs b/tvix/eval/src/value/string/mod.rs new file mode 100644 index 000000000000..5bcb4786b283 --- /dev/null +++ b/tvix/eval/src/value/string/mod.rs @@ -0,0 +1,879 @@ +//! 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; +#[cfg(feature = "no_leak")] +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; + +mod context; + +pub use context::{NixContext, NixContextElement}; + +/// 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::>>() + /// 48 + /// + /// >> std::mem::size_of::>>>() + /// 8 + /// ``` + context: Option>, + /// 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::>>(); + let (layout, len_offset) = layout.extend(Layout::new::()).unwrap(); + let (layout, data_offset) = layout.extend(Layout::array::(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) -> (Layout, usize, usize) { + let layout = Layout::new::>>(); + let (_, len_offset) = layout.extend(Layout::new::()).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 { + 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) { + 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) -> 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) -> *mut Option> { + // SAFETY: The context is the first field in the layout of the allocation + this.as_ptr() as *mut Option> + } + + /// 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) -> &'a Option> { + 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) -> &'a mut Option> { + 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) -> *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) -> &'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) -> &'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) -> NonNull { + 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, BuildNoHashHasher>, + #[cfg(feature = "no_leak")] + #[allow(clippy::disallowed_types)] // Not using the default hasher + interned_strings: FxHashSet>, +} + +unsafe impl Send for InternerInner {} + +fn hash(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); + +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); + +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 { + 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> for NixString { + fn from(value: Box) -> Self { + Self::new(&value, None) + } +} + +impl From 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> for NixString { + fn from(value: Vec) -> Self { + value.into_boxed_slice().into() + } +} + +impl From> 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 for NixString { + fn from(s: String) -> Self { + s.into_bytes().into() + } +} + +impl From<(T, Option>)> for NixString +where + NixString: From, +{ + fn from((s, ctx): (T, Option>)) -> Self { + Self::new(NixString::from(s).as_ref(), ctx) + } +} + +impl From> for NixString { + fn from(s: Box) -> Self { + s.into_boxed_bytes().into() + } +} + +impl From 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 for String, that one quotes. + +impl From 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 for NixString { + fn borrow(&self) -> &BStr { + self.as_bstr() + } +} + +impl Hash for NixString { + fn hash(&self, state: &mut H) { + self.as_bstr().hash(state) + } +} + +impl<'de> Deserialize<'de> for NixString { + fn deserialize(deserializer: D) -> Result + 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(self, v: String) -> Result + where + E: serde::de::Error, + { + Ok(v.into()) + } + + fn visit_str(self, v: &str) -> Result + 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 = ::Parameters; + + type Strategy = BoxedStrategy; + + fn arbitrary_with(args: Self::Parameters) -> Self::Strategy { + any_with::(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>) -> 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>) -> 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(other: &NixString, new_contents: T) -> Self + where + NixString: From, + { + Self::new( + Self::from(new_contents).as_ref(), + other.context().map(|c| Box::new(c.clone())), + ) + } + + pub fn new_context_from(context: NixContext, contents: T) -> Self + where + NixString: From, + { + 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 { + 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> { + // 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 { + 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 { + 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 { + 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 { + 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> { + 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 { + 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::(), 8); + } + + #[proptest] + fn clone_strings(s: NixString) { + drop(s.clone()) + } + + eq_laws!(NixString); + hash_laws!(NixString); + ord_laws!(NixString); +} -- cgit 1.4.1