//! This module implements Nix language strings.
//!
//! Nix language strings never need to be modified on the language
//! level, allowing us to shave off some memory overhead and only
//! paying the cost when creating new strings.
use bstr::{BStr, BString, ByteSlice, Chars};
use rnix::ast;
use std::alloc::{alloc, dealloc, handle_alloc_error, Layout};
use std::borrow::{Borrow, Cow};
use std::collections::HashSet;
use std::ffi::c_void;
use std::fmt::{self, Debug, Display};
use std::hash::Hash;
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(HashSet<NixContextElement>);
impl From<NixContextElement> for NixContext {
fn from(value: NixContextElement) -> Self {
Self([value].into())
}
}
impl From<HashSet<NixContextElement>> for NixContext {
fn from(value: HashSet<NixContextElement>) -> Self {
Self(value)
}
}
impl<const N: usize> From<[NixContextElement; N]> for NixContext {
fn from(value: [NixContextElement; N]) -> Self {
Self(HashSet::from(value))
}
}
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);
}
}
}
/// 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 {
fn drop(&mut self) {
// 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 {
// 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)) }
}
}
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.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 {
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()
}
}
}
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"
);
// 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);
}
