feat(tvix/eval): Initial resolution of `<...>` paths r/5087

This commit implements (lazy) resolution of `<...>` paths via either the
NIX_PATH environment variable, or the -I command-line flag - both
handled via EvalOptions. As a result, EvalOptions can no longer derive
Copy, meaning we have to clone it at each line of the repl - this is
probably not a huge deal as repl performance is not exactly an inner
loop and we're not cloning very much.

Internally, this works by creating a thunk which pushes a constant
containing the string inside the brackets to the stack, then a new
opcode to resolve that path via the `NixPath`. To get that opcode to
work, we now have to pass in the NixPath when constructing the VM.

This (intentionally) leaves out proper implementation of path resolution
via `findFile` (cppnix just calls whatever identifier called findFile is
in scope!!!) as that's widely considered a bit of a misfeature, but if
we do decide to implement that down the road it likely wouldn't be more
than a few extra ops within the thunk introduced here.

Change-Id: Ibc979b7e425b65cbe88599940520239a4a10cee2
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6918
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

1 files changed, 16 insertions, 3 deletions

diff --git a/tvix/eval/src/eval.rs b/tvix/eval/src/eval.rs
index e2495b69cdb0..809c8729f711 100644
--- a/tvix/eval/src/eval.rs
+++ b/tvix/eval/src/eval.rs
@@ -3,13 +3,14 @@ use std::{cell::RefCell, path::PathBuf, rc::Rc};
 use crate::{
     builtins::global_builtins,
     errors::{Error, ErrorKind, EvalResult},
+    nix_path::NixPath,
     observer::{DisassemblingObserver, NoOpObserver, TracingObserver},
     value::Value,
     SourceCode,
 };
 
 /// Runtime options for the Tvix interpreter
-#[derive(Debug, Clone, Copy, Default)]
+#[derive(Debug, Clone, Default)]
 #[cfg_attr(feature = "repl", derive(clap::Parser))]
 pub struct Options {
     /// Dump the raw AST to stdout before interpreting
@@ -23,6 +24,10 @@ pub struct Options {
     /// Trace the runtime of the VM
     #[cfg_attr(feature = "repl", clap(long, env = "TVIX_TRACE_RUNTIME"))]
     trace_runtime: bool,
+
+    /// A colon-separated list of directories to use to resolve `<...>`-style paths
+    #[cfg_attr(feature = "repl", clap(long, short = 'I', env = "NIX_PATH"))]
+    nix_path: Option<NixPath>,
 }
 
 pub fn interpret(code: &str, location: Option<PathBuf>, options: Options) -> EvalResult<Value> {
@@ -105,9 +110,17 @@ pub fn interpret(code: &str, location: Option<PathBuf>, options: Options) -> Eva
     }
 
     let result = if options.trace_runtime {
-        crate::vm::run_lambda(&mut TracingObserver::new(std::io::stderr()), result.lambda)
+        crate::vm::run_lambda(
+            options.nix_path.unwrap_or_default(),
+            &mut TracingObserver::new(std::io::stderr()),
+            result.lambda,
+        )
     } else {
-        crate::vm::run_lambda(&mut NoOpObserver::default(), result.lambda)
+        crate::vm::run_lambda(
+            options.nix_path.unwrap_or_default(),
+            &mut NoOpObserver::default(),
+            result.lambda,
+        )
     };
 
     if let Err(err) = &result {