feat(tvix/eval): Implement Display for io::FileType r/8463

In newer versions of Nix there's a builtins.readFileType builtin, we
should try to avoid duplicating the enum -> string conversion by
implementating Display before we implement builtins.readFileType.

Change-Id: I579e95949a76eb33d2e7bda0000ed84859df765e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12129
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: Ilan Joselevich <personal@ilanjoselevich.com>
Tested-by: BuildkiteCI

2 files changed, 14 insertions, 7 deletions

diff --git a/tvix/eval/src/builtins/impure.rs b/tvix/eval/src/builtins/impure.rs
index c82b910f5ffa..24fe0e7e9ed4 100644
--- a/tvix/eval/src/builtins/impure.rs
+++ b/tvix/eval/src/builtins/impure.rs
@@ -9,7 +9,6 @@ use std::{
 use crate::{
     self as tvix_eval,
     errors::ErrorKind,
-    io::FileType,
     value::NixAttrs,
     vm::generators::{self, GenCo},
     NixString, Value,
@@ -60,12 +59,7 @@ mod impure_builtins {
                         NixString::from(
                             String::from_utf8(name.to_vec()).expect("parsing file name as string"),
                         ),
-                        Value::from(match ftype {
-                            FileType::Directory => "directory",
-                            FileType::Regular => "regular",
-                            FileType::Symlink => "symlink",
-                            FileType::Unknown => "unknown",
-                        }),
+                        Value::from(ftype.to_string()),
                     )
                 });
 
diff --git a/tvix/eval/src/io.rs b/tvix/eval/src/io.rs
index abe0e0518303..e4bad7b11ce0 100644
--- a/tvix/eval/src/io.rs
+++ b/tvix/eval/src/io.rs
@@ -35,6 +35,19 @@ pub enum FileType {
     Unknown,
 }
 
+impl std::fmt::Display for FileType {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let type_as_str = match &self {
+            FileType::Directory => "directory",
+            FileType::Regular => "regular",
+            FileType::Symlink => "symlink",
+            FileType::Unknown => "unknown",
+        };
+
+        write!(f, "{}", type_as_str)
+    }
+}
+
 /// Represents all possible filesystem interactions that exist in the Nix
 /// language, and that need to be executed somehow.
 ///