feat(tvix/tests): Import default.nix inside directory

This requires actually passing the source directory into `interpret` in
the eval tests, but otherwise this is fairly straightforward - if we're
trying to import a directory, just push `default.nix` onto it and import
that instead.

Change-Id: I0b7d4234f81977e78d14dfa651bf0cf9721017e5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6893
Autosubmit: grfn <grfn@gws.fyi>
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

tvix/eval/src/builtins/impure.rs

@@ -52,7 +52,10 @@ pub fn builtins_import(
         "import",
         &[true],
         move |mut args: Vec<Value>, vm: &mut VM| {
-            let path = super::coerce_value_to_path(&args.pop().unwrap(), vm)?;
+            let mut path = super::coerce_value_to_path(&args.pop().unwrap(), vm)?;
+            if path.is_dir() {
+                path.push("default.nix");
+            }
 
             let contents =
                 std::fs::read_to_string(&path).map_err(|err| ErrorKind::ReadFileError {

tvix/eval/src/tests/mod.rs

@@ -12,7 +12,7 @@ fn eval_okay_test(code_path: &str) {
     let code = std::fs::read_to_string(code_path).expect("should be able to read test code");
     let exp = std::fs::read_to_string(exp_path).expect("should be able to read test expectation");
 
-    let result = interpret(&code, None, Default::default())
+    let result = interpret(&code, Some(code_path.into()), Default::default())
         .expect("evaluation of eval-okay test should succeed");
     let result_str = format!("{}", result);
 

tvix/eval/src/tests/tvix_tests/directory/default.nix

@@ -0,0 +1 @@
+42

tvix/eval/src/tests/tvix_tests/eval-okay-import.exp

@@ -0,0 +1 @@
+[ 42 42 ]

tvix/eval/src/tests/tvix_tests/eval-okay-import.nix

@@ -0,0 +1,4 @@
+[
+  (import ./directory)
+  (import ./directory/default.nix)
+]