From b3e24cb3e53eabf47b5857043e13cc6473aebaa7 Mon Sep 17 00:00:00 2001
From: Qyriad <qyriad@qyriad.me>
Date: Tue, 18 Nov 2025 12:23:53 +0100
Subject: [PATCH] new option: abort-on-warn

Co-authored-by: Emilia Bopp <contact@ebopp.de>

Change-Id: I3c3347e51d8543fbeb2b4e6ed12b0f556a6a6964
---
 doc/manual/rl-next/builtins-warn.md                    |  4 +++-
 lix/libexpr/meson.build                                |  1 +
 lix/libexpr/primops.cc                                 |  5 +++++
 lix/libexpr/settings/abort-on-warn.md                  | 10 ++++++++++
 .../lang/builtins.warn/eval-fail-abort.err.exp         |  9 +++++++++
 tests/functional2/lang/builtins.warn/in-abort.nix      |  1 +
 tests/functional2/lang/builtins.warn/test.toml         |  5 +++++
 7 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 lix/libexpr/settings/abort-on-warn.md
 create mode 100644 tests/functional2/lang/builtins.warn/eval-fail-abort.err.exp
 create mode 100644 tests/functional2/lang/builtins.warn/in-abort.nix

diff --git a/doc/manual/rl-next/builtins-warn.md b/doc/manual/rl-next/builtins-warn.md
index b474866d0..c5c6e2b9e 100644
--- a/doc/manual/rl-next/builtins-warn.md
+++ b/doc/manual/rl-next/builtins-warn.md
@@ -10,4 +10,6 @@ Like `builtins.trace`, it takes two arguments: the message to emit, and the expr
 _Unlike_ `builtins.trace`, `builtins.warn` requires the first argument — the message — to be a string.
 In the future we may extend `builtins.warn` to accept a more structured API.
 
-To go along with this, we also have a new config setting [`debugger-on-warn`](@docroot@/command-ref/conf-file.md#conf-debugger-on-warn), which, when used with `--debugger`, makes `builtins.warn` also function like [`builtins.break`](@docroot@/language/builtins.md#builtins-break).
+To go along with this, we also have two new config settings:
+- [`debugger-on-warn`](@docroot@/command-ref/conf-file.md#conf-debugger-on-warn), which, when used with `--debugger`, makes `builtins.warn` also function like [`builtins.break`](@docroot@/language/builtins.md#builtins-break).
+- [`abort-on-warn`](@docroot@/command-ref/conf-file.md#conf-abort-on-warn), which aborts evaluation entirely after the warning is emitted.
diff --git a/lix/libexpr/meson.build b/lix/libexpr/meson.build
index 0e56b9139..c33d35022 100644
--- a/lix/libexpr/meson.build
+++ b/lix/libexpr/meson.build
@@ -15,6 +15,7 @@ subdir('flake')
 
 libexpr_setting_definitions = files(
   # keep-sorted start
+  'settings/abort-on-warn.md',
   'settings/allow-import-from-derivation.md',
   'settings/allow-unsafe-native-code-during-evaluation.md',
   'settings/allowed-uris.md',
diff --git a/lix/libexpr/primops.cc b/lix/libexpr/primops.cc
index 32d65dbd7..8a472aaef 100644
--- a/lix/libexpr/primops.cc
+++ b/lix/libexpr/primops.cc
@@ -779,6 +779,11 @@ static void prim_warn(EvalState & state, Value ** args, Value & v)
 
     printTaggedWarning("%s", Uncolored(msg));
 
+    if (evalSettings.abortOnWarn) {
+        state.ctx.errors.make<Abort>("evaluation aborted (abort-on-warn)")
+            .debugThrow();
+    }
+
     if (evalSettings.debuggerOnWarn) {
         if (auto const trace = state.ctx.nextDebugTrace()) {
             auto const error = EvalError(ErrorInfo{
diff --git a/lix/libexpr/settings/abort-on-warn.md b/lix/libexpr/settings/abort-on-warn.md
new file mode 100644
index 000000000..61d881273
--- /dev/null
+++ b/lix/libexpr/settings/abort-on-warn.md
@@ -0,0 +1,10 @@
+---
+name: abort-on-warn
+internalName: abortOnWarn
+type: bool
+default: false
+---
+If set to true, [`builtins.warn`](@docroot@/language/builtins.md#builtins-warn) will throw an error when logging a warning.
+This will give you a stack trace that leads to the location of the warning.
+This is useful for finding information about warnings in third-party Nix code when you can not start the interactive debugger, such as when Nix is called from a non-interactive script. See [`debugger-on-warn`](#conf-debugger-on-warn).
+Currently, a stack trace can only be produced when the debugger is enabled, or when evaluation is aborted.
diff --git a/tests/functional2/lang/builtins.warn/eval-fail-abort.err.exp b/tests/functional2/lang/builtins.warn/eval-fail-abort.err.exp
new file mode 100644
index 000000000..0dbea23c8
--- /dev/null
+++ b/tests/functional2/lang/builtins.warn/eval-fail-abort.err.exp
@@ -0,0 +1,9 @@
+warning: meow
+error:
+       … while calling the 'warn' builtin
+         at /pwd/in.nix:1:1:
+            1| builtins.warn "meow" (throw "must abort before this")
+             | ^
+            2|
+
+       error: evaluation aborted (abort-on-warn)
diff --git a/tests/functional2/lang/builtins.warn/in-abort.nix b/tests/functional2/lang/builtins.warn/in-abort.nix
new file mode 100644
index 000000000..e838bbd46
--- /dev/null
+++ b/tests/functional2/lang/builtins.warn/in-abort.nix
@@ -0,0 +1 @@
+builtins.warn "meow" (throw "must abort before this")
diff --git a/tests/functional2/lang/builtins.warn/test.toml b/tests/functional2/lang/builtins.warn/test.toml
index db3224037..06af43cfb 100644
--- a/tests/functional2/lang/builtins.warn/test.toml
+++ b/tests/functional2/lang/builtins.warn/test.toml
@@ -4,3 +4,8 @@ runner = "eval-okay"
 [[test]]
 runner = "eval-fail"
 in = "in-reject-non-string.nix"
+
+[[test]]
+runner = "eval-fail"
+flags = ["--option", "abort-on-warn", "true"]
+in = "in-abort.nix"