1 files changed, 200 insertions, 0 deletions
diff --git a/tvix/nix-compat/src/derivation/write.rs b/tvix/nix-compat/src/derivation/write.rs
new file mode 100644
index 000000000000..9a6234424816
--- /dev/null
+++ b/tvix/nix-compat/src/derivation/write.rs
@@ -0,0 +1,200 @@
+//! This module implements the serialisation of derivations into the
+//! [ATerm][] format used by C++ Nix.
+//!
+//! [ATerm]: http://program-transformation.org/Tools/ATermFormat.html
+
+use crate::derivation::escape::escape_bytes;
+use crate::derivation::output::Output;
+use bstr::BString;
+use std::{
+    collections::{BTreeMap, BTreeSet},
+    io,
+    io::Error,
+    io::Write,
+};
+
+pub const DERIVATION_PREFIX: &str = "Derive";
+pub const PAREN_OPEN: char = '(';
+pub const PAREN_CLOSE: char = ')';
+pub const BRACKET_OPEN: char = '[';
+pub const BRACKET_CLOSE: char = ']';
+pub const COMMA: char = ',';
+pub const QUOTE: char = '"';
+
+// Writes a character to the writer.
+pub(crate) fn write_char(writer: &mut impl Write, c: char) -> io::Result<()> {
+    let mut buf = [0; 4];
+    let b = c.encode_utf8(&mut buf).as_bytes();
+    writer.write_all(b)
+}
+
+// Write a string `s` as a quoted field to the writer.
+// The `escape` argument controls whether escaping will be skipped.
+// This is the case if `s` is known to only contain characters that need no
+// escaping.
+pub(crate) fn write_field<S: AsRef<[u8]>>(
+    writer: &mut impl Write,
+    s: S,
+    escape: bool,
+) -> io::Result<()> {
+    write_char(writer, QUOTE)?;
+
+    if !escape {
+        writer.write_all(s.as_ref())?;
+    } else {
+        writer.write_all(&escape_bytes(s.as_ref()))?;
+    }
+
+    write_char(writer, QUOTE)?;
+
+    Ok(())
+}
+
+fn write_array_elements<S: AsRef<[u8]>>(
+    writer: &mut impl Write,
+    elements: &[S],
+) -> Result<(), io::Error> {
+    for (index, element) in elements.iter().enumerate() {
+        if index > 0 {
+            write_char(writer, COMMA)?;
+        }
+
+        write_field(writer, element, true)?;
+    }
+
+    Ok(())
+}
+
+pub fn write_outputs(
+    writer: &mut impl Write,
+    outputs: &BTreeMap<String, Output>,
+) -> Result<(), io::Error> {
+    write_char(writer, BRACKET_OPEN)?;
+    for (ii, (output_name, output)) in outputs.iter().enumerate() {
+        if ii > 0 {
+            write_char(writer, COMMA)?;
+        }
+
+        write_char(writer, PAREN_OPEN)?;
+
+        let mut elements: Vec<&str> = vec![output_name, &output.path];
+
+        let (e2, e3) = match &output.hash_with_mode {
+            Some(hash) => match hash {
+                crate::nixhash::NixHashWithMode::Flat(h) => (
+                    h.algo.to_string(),
+                    data_encoding::HEXLOWER.encode(&h.digest),
+                ),
+                crate::nixhash::NixHashWithMode::Recursive(h) => (
+                    format!("r:{}", h.algo),
+                    data_encoding::HEXLOWER.encode(&h.digest),
+                ),
+            },
+            None => ("".to_string(), "".to_string()),
+        };
+
+        elements.push(&e2);
+        elements.push(&e3);
+
+        write_array_elements(writer, &elements)?;
+
+        write_char(writer, PAREN_CLOSE)?;
+    }
+    write_char(writer, BRACKET_CLOSE)?;
+
+    Ok(())
+}
+
+pub fn write_input_derivations(
+    writer: &mut impl Write,
+    input_derivations: &BTreeMap<String, BTreeSet<String>>,
+) -> Result<(), io::Error> {
+    write_char(writer, BRACKET_OPEN)?;
+
+    for (ii, (input_derivation_path, input_derivation)) in input_derivations.iter().enumerate() {
+        if ii > 0 {
+            write_char(writer, COMMA)?;
+        }
+
+        write_char(writer, PAREN_OPEN)?;
+        write_field(writer, input_derivation_path.as_str(), false)?;
+        write_char(writer, COMMA)?;
+
+        write_char(writer, BRACKET_OPEN)?;
+        write_array_elements(
+            writer,
+            &input_derivation
+                .iter()
+                .map(String::as_bytes)
+                .collect::<Vec<_>>(),
+        )?;
+        write_char(writer, BRACKET_CLOSE)?;
+
+        write_char(writer, PAREN_CLOSE)?;
+    }
+
+    write_char(writer, BRACKET_CLOSE)?;
+
+    Ok(())
+}
+
+pub fn write_input_sources(
+    writer: &mut impl Write,
+    input_sources: &BTreeSet<String>,
+) -> Result<(), io::Error> {
+    write_char(writer, BRACKET_OPEN)?;
+    write_array_elements(
+        writer,
+        &input_sources.iter().map(String::from).collect::<Vec<_>>(),
+    )?;
+    write_char(writer, BRACKET_CLOSE)?;
+
+    Ok(())
+}
+
+pub fn write_system(writer: &mut impl Write, platform: &str) -> Result<(), Error> {
+    write_field(writer, platform, true)?;
+    Ok(())
+}
+
+pub fn write_builder(writer: &mut impl Write, builder: &str) -> Result<(), Error> {
+    write_field(writer, builder, true)?;
+    Ok(())
+}
+
+pub fn write_arguments(writer: &mut impl Write, arguments: &[String]) -> Result<(), io::Error> {
+    write_char(writer, BRACKET_OPEN)?;
+    write_array_elements(
+        writer,
+        &arguments
+            .iter()
+            .map(|s| s.as_bytes().to_vec().into())
+            .collect::<Vec<BString>>(),
+    )?;
+    write_char(writer, BRACKET_CLOSE)?;
+
+    Ok(())
+}
+
+pub fn write_enviroment(
+    writer: &mut impl Write,
+    environment: &BTreeMap<String, BString>,
+) -> Result<(), io::Error> {
+    write_char(writer, BRACKET_OPEN)?;
+
+    for (i, (k, v)) in environment.iter().enumerate() {
+        if i > 0 {
+            write_char(writer, COMMA)?;
+        }
+
+        write_char(writer, PAREN_OPEN)?;
+        write_field(writer, k, false)?;
+        write_char(writer, COMMA)?;
+        write_field(writer, v, true)?;
+        write_char(writer, PAREN_CLOSE)?;
+    }
+
+    write_char(writer, BRACKET_CLOSE)?;
+
+    Ok(())
+}