2 files changed, 80 insertions, 6 deletions
diff --git a/tvix/eval/src/builtins/impure.rs b/tvix/eval/src/builtins/impure.rs
index 7073deaaa7ac..675bdd50950e 100644
--- a/tvix/eval/src/builtins/impure.rs
+++ b/tvix/eval/src/builtins/impure.rs
@@ -1,19 +1,23 @@
 use std::{
-    collections::BTreeMap,
+    collections::{BTreeMap, HashMap},
+    rc::Rc,
     time::{SystemTime, UNIX_EPOCH},
 };
 
 use crate::{
-    value::{Builtin, NixString},
-    Value,
+    errors::ErrorKind,
+    observer::NoOpObserver,
+    value::{Builtin, NixString, Thunk},
+    vm::VM,
+    SourceCode, Value,
 };
 
 fn impure_builtins() -> Vec<Builtin> {
     vec![]
 }
 
-/// Return all impure builtins, that is all builtins which may perform I/O outside of the VM and so
-/// cannot be used in all contexts (e.g. WASM).
+/// Return all impure builtins, that is all builtins which may perform I/O
+/// outside of the VM and so cannot be used in all contexts (e.g. WASM).
 pub(super) fn builtins() -> BTreeMap<NixString, Value> {
     let mut map: BTreeMap<NixString, Value> = impure_builtins()
         .into_iter()
@@ -34,3 +38,73 @@ pub(super) fn builtins() -> BTreeMap<NixString, Value> {
 
     map
 }
+
+/// Constructs and inserts the `import` builtin. This builtin is special in that
+/// it needs to capture the [crate::SourceCode] structure to correctly track
+/// source code locations while invoking a compiler.
+// TODO: need to be able to pass through a CompilationObserver, too.
+pub fn builtins_import(source: SourceCode) -> Builtin {
+    Builtin::new(
+        "import",
+        &[true],
+        move |mut args: Vec<Value>, _: &mut VM| {
+            let path = match args.pop().unwrap() {
+                Value::Path(path) => path,
+                Value::String(_) => {
+                    return Err(ErrorKind::NotImplemented("importing from string-paths"))
+                }
+                other => {
+                    return Err(ErrorKind::TypeError {
+                        expected: "path or string",
+                        actual: other.type_of(),
+                    })
+                }
+            };
+
+            let contents =
+                std::fs::read_to_string(&path).map_err(|err| ErrorKind::ReadFileError {
+                    path: path.clone(),
+                    error: Rc::new(err),
+                })?;
+
+            let parsed = rnix::ast::Root::parse(&contents);
+            let errors = parsed.errors();
+
+            if !errors.is_empty() {
+                return Err(ErrorKind::ImportParseError {
+                    path,
+                    errors: errors.to_vec(),
+                });
+            }
+
+            let file = source.add_file(path.to_string_lossy().to_string(), contents);
+
+            let result = crate::compile(
+                &parsed.tree().expr().unwrap(),
+                Some(path.clone()),
+                file,
+                HashMap::new(), // TODO: pass through globals
+                &mut NoOpObserver::default(),
+            )
+            .map_err(|err| ErrorKind::ImportCompilerError {
+                path: path.clone(),
+                errors: vec![err],
+            })?;
+
+            if !result.errors.is_empty() {
+                return Err(ErrorKind::ImportCompilerError {
+                    path,
+                    errors: result.errors,
+                });
+            }
+
+            // TODO: deal with runtime *warnings* (most likely through an
+            // emit_warning function on the VM that might return it together with
+            // the result)
+
+            // Compilation succeeded, we can construct a thunk from whatever it spat
+            // out and return that.
+            Ok(Value::Thunk(Thunk::new(result.lambda)))
+        },
+    )
+}
diff --git a/tvix/eval/src/builtins/mod.rs b/tvix/eval/src/builtins/mod.rs
index ad3ab807e3d1..b0aab352d23b 100644
--- a/tvix/eval/src/builtins/mod.rs
+++ b/tvix/eval/src/builtins/mod.rs
@@ -19,7 +19,7 @@ use crate::{arithmetic_op, cmp_op};
 use self::versions::{VersionPart, VersionPartsIter};
 
 #[cfg(feature = "impure")]
-mod impure;
+pub mod impure;
 pub mod versions;
 
 /// Coerce a Nix Value to a plain path, e.g. in order to access the file it