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use std::{borrow::Cow, fmt::Display};
/// This module implements Nix language strings and their different
/// backing implementations.
#[derive(Clone, Debug, Hash, Eq, Ord)]
pub enum NixString {
Static(&'static str),
Heap(String),
}
impl PartialEq for NixString {
fn eq(&self, other: &Self) -> bool {
self.as_str() == other.as_str()
}
}
impl PartialOrd for NixString {
fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
self.as_str().partial_cmp(other.as_str())
}
}
impl From<&'static str> for NixString {
fn from(s: &'static str) -> Self {
NixString::Static(s)
}
}
impl From<String> for NixString {
fn from(s: String) -> Self {
NixString::Heap(s)
}
}
impl NixString {
pub const NAME: Self = NixString::Static("name");
pub const VALUE: Self = NixString::Static("value");
pub fn as_str(&self) -> &str {
match self {
NixString::Static(s) => s,
NixString::Heap(s) => s,
}
}
// 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 = nix_escape_string(self.as_str());
match escaped {
// A borrowed string is unchanged and can be returned as
// is.
Cow::Borrowed(_) => 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.as_str().to_owned();
s.push_str(other.as_str());
NixString::Heap(s)
}
}
fn nix_escape_char(ch: char) -> Option<&'static str> {
match ch {
'\\' => Some("\\"),
'"' => Some("\\"),
'\n' => Some("\\n"),
_ => None,
}
}
// 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> {
for (i, c) in input.chars().enumerate() {
if let Some(esc) = nix_escape_char(c) {
let mut escaped = String::with_capacity(input.len());
escaped.push_str(&input[..i]);
escaped.push_str(esc);
for c in input[i + 1..].chars() {
match nix_escape_char(c) {
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.as_str()))?;
f.write_str("\"")
}
}
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