snix_eval/compiler/
import.rs

1//! This module implements the Nix language's `import` feature, which
2//! is exposed as a builtin in the Nix language.
3//!
4//! This is not a typical builtin, as it needs access to internal
5//! compiler and VM state (such as the [`crate::SourceCode`]
6//! instance, or observers).
7
8use super::GlobalsMap;
9use genawaiter::rc::Gen;
10use std::rc::Weak;
11
12use crate::{
13    ErrorKind, SourceCode, Value,
14    builtins::coerce_value_to_path,
15    generators::pin_generator,
16    try_cek_to_value,
17    value::{Builtin, Thunk},
18    vm::generators::{self, GenCo},
19};
20
21async fn import_impl(
22    co: GenCo,
23    globals: Weak<GlobalsMap>,
24    source: SourceCode,
25    mut args: Vec<Value>,
26) -> Result<Value, ErrorKind> {
27    // TODO(sterni): canon_path()?
28    let mut path = try_cek_to_value!(coerce_value_to_path(&co, args.pop().unwrap()).await?);
29
30    if path.is_dir() {
31        path.push("default.nix");
32    }
33
34    if let Some(cached) = generators::request_import_cache_lookup(&co, path.clone()).await {
35        return Ok(cached);
36    }
37
38    let mut reader = generators::request_open_file(&co, path.clone()).await;
39    // We read to a String instead of a Vec<u8> because rnix only supports
40    // string source files.
41    let mut contents = String::new();
42    reader.read_to_string(&mut contents)?;
43
44    let parsed = rnix::ast::Root::parse(&contents);
45    let errors = parsed.errors();
46    let file = source.add_file(path.to_string_lossy().to_string(), contents.to_owned());
47
48    if !errors.is_empty() {
49        return Err(ErrorKind::ImportParseError {
50            path,
51            file,
52            errors: errors.to_vec(),
53        });
54    }
55
56    let result = crate::compiler::compile(
57        &parsed.tree().expr().unwrap(),
58        Some(path.clone()),
59        // The VM must ensure that a strong reference to the globals outlives
60        // any self-references (which are weak) embedded within the globals. If
61        // the expect() below panics, it means that did not happen.
62        globals
63            .upgrade()
64            .expect("globals dropped while still in use"),
65        None,
66        &source,
67        &file,
68        Default::default(),
69    )
70    .map_err(|err| ErrorKind::ImportCompilerError {
71        path: path.clone(),
72        errors: vec![err],
73    })?;
74
75    if !result.errors.is_empty() {
76        return Err(ErrorKind::ImportCompilerError {
77            path,
78            errors: result.errors,
79        });
80    }
81
82    for warning in result.warnings {
83        generators::emit_warning(&co, warning).await;
84    }
85
86    // Compilation succeeded, we can construct a thunk from whatever it spat
87    // out and return that.
88    let res = Value::Thunk(Thunk::new_suspended(
89        result.lambda,
90        generators::request_span(&co).await,
91    ));
92
93    generators::request_import_cache_put(&co, path, res.clone()).await;
94
95    Ok(res)
96}
97
98/// Constructs the `import` builtin. This builtin is special in that
99/// it needs to capture the [crate::SourceCode] structure to correctly
100/// track source code locations while invoking a compiler.
101// TODO: need to be able to pass through a CompilationObserver, too.
102// TODO: can the `SourceCode` come from the compiler?
103pub(super) fn builtins_import(globals: &Weak<GlobalsMap>, source: SourceCode) -> Builtin {
104    // This (very cheap, once-per-compiler-startup) clone exists
105    // solely in order to keep the borrow checker happy.  It
106    // resolves the tension between the requirements of
107    // Rc::new_cyclic() and Builtin::new()
108    let globals = globals.clone();
109
110    Builtin::new(
111        "import",
112        Some("Import the given file and return the Nix value it evaluates to"),
113        1,
114        move |args| {
115            Gen::new(|co| pin_generator(import_impl(co, globals.clone(), source.clone(), args)))
116        },
117    )
118}
snix_eval/compiler/import.rs

snix_eval/compiler/
import.rs
