made EXPR_PATH point to local instead of store

- we need this behavior in dev shell
- the main build still uses the store file

pkgs/test/nixpkgs-check-by-name/default.nix

@@ -8,7 +8,7 @@
   makeWrapper,
 }:
 let
-  runtimeExprPath = "${./src/eval.nix}";
+  runtimeExprPath = ./src/eval.nix;
   package =
     rustPlatform.buildRustPackage {
       name = "nixpkgs-check-by-name";
@@ -20,7 +20,7 @@ let
         clippy
         makeWrapper
       ];
-      env.NIX_CHECK_BY_NAME_EXPR_PATH = runtimeExprPath;
+      env.NIX_CHECK_BY_NAME_EXPR_PATH = "${runtimeExprPath}";
       # Needed to make Nix evaluation work inside the nix build
       preCheck = ''
         export TEST_ROOT=$(pwd)/test-tmp
@@ -43,7 +43,7 @@ let
           --set NIX_CHECK_BY_NAME_EXPR_PATH "$NIX_CHECK_BY_NAME_EXPR_PATH"
       '';
       passthru.shell = mkShell {
-        env.NIX_CHECK_BY_NAME_EXPR_PATH = runtimeExprPath;
+        env.NIX_CHECK_BY_NAME_EXPR_PATH = toString runtimeExprPath;
         inputsFrom = [ package ];
       };
     };

pkgs/test/nixpkgs-check-by-name/src/eval.rs

@@ -58,7 +58,8 @@ pub fn check_values(
         attrs_file_path.display()
     ))?;
 
-    let expr_path = std::env::var("NIX_CHECK_BY_NAME_EXPR_PATH")?;
+    let expr_path = std::env::var("NIX_CHECK_BY_NAME_EXPR_PATH")
+        .context("Could not get environment variable NIX_CHECK_BY_NAME_EXPR_PATH")?;
     // With restrict-eval, only paths in NIX_PATH can be accessed, so we explicitly specify the
     // ones needed needed
     let mut command = process::Command::new("nix-instantiate");