From d46f741cdfcb4b9b6aed5532dec7fe62f1e3cb72 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Wed, 30 Apr 2025 22:29:27 +0200
Subject: [PATCH] Complain when using --pure-eval with --file

This never worked and cannot work because in pure eval mode, the
evaluator doesn't have access to the file.
---
 src/libcmd/installables.cc | 6 +++++-
 tests/functional/eval.sh   | 3 +++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index 1c414e9e2..080557d4f 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -491,7 +491,11 @@ Installables SourceExprCommand::parseInstallables(
             throw UsageError("'--file' and '--expr' are exclusive");
 
         // FIXME: backward compatibility hack
-        if (file) evalSettings.pureEval = false;
+        if (file) {
+            if (evalSettings.pureEval && evalSettings.pureEval.overridden)
+                throw UsageError("'--file' is not compatible with '--pure-eval'");
+            evalSettings.pureEval = false;
+        }
 
         auto state = getEvalState();
         auto vFile = state->allocValue();
diff --git a/tests/functional/eval.sh b/tests/functional/eval.sh
index ed9c214f5..f876f5ac4 100755
--- a/tests/functional/eval.sh
+++ b/tests/functional/eval.sh
@@ -39,6 +39,9 @@ nix-instantiate --eval -E 'assert 1 + 2 == 3; true'
 ln -sfn cycle.nix "$TEST_ROOT/cycle.nix"
 (! nix eval --file "$TEST_ROOT/cycle.nix")
 
+# --file and --pure-eval don't mix.
+expectStderr 1 nix eval --pure-eval --file "$TEST_ROOT/cycle.nix" | grepQuiet "not compatible"
+
 # Check that relative symlinks are resolved correctly.
 mkdir -p "$TEST_ROOT/xyzzy" "$TEST_ROOT/foo"
 ln -sfn ../xyzzy "$TEST_ROOT/foo/bar"