From 54322f09d353e296b06ce8b1f4264749a7ccd489 Mon Sep 17 00:00:00 2001
From: Qyriad <qyriad@qyriad.me>
Date: Tue, 7 May 2024 18:28:29 -0600
Subject: nix3-eval: don't elide top-level errors

Fixes #276.

Change-Id: I83e71beb5c35d6f3b10a4186caa5e52a2f95b510
---
 src/nix/eval.cc          | 4 +++-
 tests/functional/eval.sh | 9 +++++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/nix/eval.cc b/src/nix/eval.cc
index a9e4c8968..469ff7391 100644
--- a/src/nix/eval.cc
+++ b/src/nix/eval.cc
@@ -1,5 +1,6 @@
 #include "command-installable-value.hh"
 #include "common-args.hh"
+#include "print-options.hh"
 #include "shared.hh"
 #include "store-api.hh"
 #include "eval.hh"
@@ -127,7 +128,8 @@ struct CmdEval : MixJSON, InstallableValueCommand, MixReadOnlyOption
                     *v,
                     PrintOptions {
                         .force = true,
-                        .derivationPaths = true
+                        .derivationPaths = true,
+                        .errors = ErrorPrintBehavior::ThrowTopLevel,
                     }
                 )
             );
diff --git a/tests/functional/eval.sh b/tests/functional/eval.sh
index 0e789cc47..2b34caddb 100644
--- a/tests/functional/eval.sh
+++ b/tests/functional/eval.sh
@@ -22,6 +22,15 @@ nix eval -E 'assert 1 + 2 == 3; true'
 [[ $(nix eval int -f - < "./eval.nix") == 123 ]]
 [[ "$(nix eval --expr '{"assert"=1;bar=2;}')" == '{ "assert" = 1; bar = 2; }' ]]
 
+# Top-level eval errors should be printed to stderr with a traceback.
+topLevelThrow="$(expectStderr 1 nix eval --expr 'throw "a sample throw message"')"
+[[ "$topLevelThrow" =~ "a sample throw message" ]]
+[[ "$topLevelThrow" =~ "while calling the 'throw' builtin" ]]
+
+# But errors inside something should print an elided version, and exit with 0.
+outputOfNestedThrow="$(nix eval --expr '{ throws = throw "a sample throw message"; }')"
+[[ "${outputOfNestedThrow}" == "{ throws = «error: a sample throw message»; }" ]]
+
 # Check if toFile can be utilized during restricted eval
 [[ $(nix eval --restrict-eval --expr 'import (builtins.toFile "source" "42")') == 42 ]]
 
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