Fix tests for nixVersions.minimum

This is important because that's the Nix version that should really be used in CI

CONTRIBUTING.md

@@ -61,6 +61,10 @@ Integration tests are declared in [`./tests`](./tests) as subdirectories imitati
   A file containing the expected standard output.
   The default is expecting an empty standard output.
 
+  This file is matched against the error almost literally,
+  with the only exception being that the `@REDACTED@` string can match anything,
+  which is useful for non-deterministic errors.
+
 ## Automation
 
 Pinned dependencies are [regularly updated automatically](./.github/workflows/update.yml).

package.nix

@@ -9,6 +9,7 @@
   nixVersionsToTest ? [
     nix
     nixVersions.stable
+    nixVersions.minimum
   ],
 
   nixpkgsLibPath,

src/main.rs

@@ -181,6 +181,7 @@ mod tests {
     use crate::process;
     use crate::utils;
     use anyhow::Context;
+    use std::ffi::OsStr;
     use std::fs;
     use std::path::Path;
     use tempfile::{tempdir_in, TempDir};
@@ -277,14 +278,24 @@ mod tests {
         } else {
             Path::new("tests/empty-base")
         };
+        // Empty dir, needed so that no warnings are printed when testing older Nix versions
+        // that don't recognise certain newer keys in nix.conf
+        let nix_conf_dir = tempdir()?;
 
         // We don't want coloring to mess up the tests
-        let writer = temp_env::with_var("NO_COLOR", Some("1"), || -> anyhow::Result<_> {
-            let mut writer = vec![];
-            process(base_nixpkgs.to_owned(), path.to_owned(), true, &mut writer)
-                .with_context(|| format!("Failed test case {name}"))?;
-            Ok(writer)
-        })?;
+        let writer = temp_env::with_vars(
+            [
+                ("NO_COLOR", Some(OsStr::new("1"))),
+                // See above comment on nix_conf_dir
+                ("NIX_CONF_DIR", Some(nix_conf_dir.path().as_os_str())),
+            ],
+            || -> anyhow::Result<_> {
+                let mut writer = vec![];
+                process(base_nixpkgs.to_owned(), path.to_owned(), true, &mut writer)
+                    .with_context(|| format!("Failed test case {name}"))?;
+                Ok(writer)
+            },
+        )?;
 
         let expr_path = std::env::var("NIX_CHECK_BY_NAME_EXPR_PATH")
             .with_context(|| "Could not get environment variable NIX_CHECK_BY_NAME_EXPR_PATH")?;
@@ -293,7 +304,16 @@ mod tests {
         // on the output, which we need to relativise for the tests to succeed everywhere
         let actual_errors = String::from_utf8_lossy(&writer).replace(&expr_path, "src/eval.nix");
 
-        if actual_errors != expected_errors {
+        let pattern = format!(
+            "^{}$",
+            regex::escape(expected_errors).replace("@REDACTED@", ".*")
+        );
+
+        let expected_errors_regex = regex::RegexBuilder::new(&pattern)
+            .dot_matches_new_line(true)
+            .build()?;
+
+        if !expected_errors_regex.is_match(&actual_errors) {
             panic!(
                 "Failed test case {name}, expected these errors:\n=======\n{}\n=======\n\
                 but got these:\n=======\n{}\n=======",

tests/by-name-failure/expected

@@ -1,20 +1,4 @@
 trace: This should be on stderr!
-error:
-       … while evaluating list element at index 3
-
-       … while evaluating list element at index 1
-
-       … while evaluating attribute 'ByName'
-
-         at src/eval.nix:76:7:
-
-           75|       inherit name;
-           76|       value.ByName =
-             |       ^
-           77|         if !pkgs ? ${name} then
-
-       (stack trace truncated; use '--show-trace' to show the full trace)
-
-       error: This is an error!
+@REDACTED@error: This is an error!@REDACTED@
 - Nix evaluation failed for some package in `pkgs/by-name`, see error above
 This PR introduces the problems listed above. Please fix them before merging, otherwise the base branch would break.