From f4c92f8872006dd95985589a229bb532943d6a89 Mon Sep 17 00:00:00 2001
From: eldritch horrors <pennae@lix.systems>
Date: Sat, 28 Feb 2026 13:19:13 +0100
Subject: [PATCH] testing: migrate function-trace.sh

Change-Id: I44bd28165070f55f21b052bc02ba6f2ea5787a1d
---
 tests/functional/function-trace.sh            | 69 -------------------
 tests/functional/meson.build                  |  1 -
 tests/functional2/eval/test_function_trace.py | 42 +++++++++++
 3 files changed, 42 insertions(+), 70 deletions(-)
 delete mode 100755 tests/functional/function-trace.sh
 create mode 100644 tests/functional2/eval/test_function_trace.py

diff --git a/tests/functional/function-trace.sh b/tests/functional/function-trace.sh
deleted file mode 100755
index 71f18b67f..000000000
--- a/tests/functional/function-trace.sh
+++ /dev/null
@@ -1,69 +0,0 @@
-#!/usr/bin/env bash
-
-source common.sh
-
-set +x
-
-expect_trace() {
-    expr="$1"
-    expect="$2"
-    actual=$(
-        nix-instantiate \
-            --trace-function-calls \
-            --expr "$expr" 2>&1 \
-            | grep "function-trace" \
-            | sed -e 's/ [0-9]*$//' \
-            || true
-    )
-
-    echo -n "Tracing expression '$expr'"
-    msg=$(diff -swB \
-               <(echo "$expect") \
-               <(echo "$actual")
-    ) && result=0 || result=$?
-    if [ $result -eq 0 ]; then
-        echo " ok."
-    else
-        echo " failed. difference:"
-        echo "$msg"
-        return $result
-    fi
-}
-
-# failure inside a tryEval
-expect_trace 'builtins.tryEval (throw "example")' "
-function-trace entered «string»:1:1 at
-function-trace entered «string»:1:19 at
-function-trace exited «string»:1:19 at
-function-trace exited «string»:1:1 at
-"
-
-# Missing argument to a formal function
-expect_trace '({ x }: x) { }' "
-function-trace entered «string»:1:1 at
-function-trace exited «string»:1:1 at
-"
-
-# Too many arguments to a formal function
-expect_trace '({ x }: x) { x = "x"; y = "y"; }' "
-function-trace entered «string»:1:1 at
-function-trace exited «string»:1:1 at
-"
-
-# Not enough arguments to a lambda
-expect_trace '(x: y: x + y) 1' "
-function-trace entered «string»:1:1 at
-function-trace exited «string»:1:1 at
-"
-
-# Too many arguments to a lambda
-expect_trace '(x: x) 1 2' "
-function-trace entered «string»:1:1 at
-function-trace exited «string»:1:1 at
-"
-
-# Not a function
-expect_trace '1 2' "
-function-trace entered «string»:1:1 at
-function-trace exited «string»:1:1 at
-"
diff --git a/tests/functional/meson.build b/tests/functional/meson.build
index e1af80e6b..816ee6cdc 100644
--- a/tests/functional/meson.build
+++ b/tests/functional/meson.build
@@ -92,7 +92,6 @@ functional_tests_scripts = [
   'nix-copy-ssh-ng.sh',
   'pre-hook.sh',
   'post-hook.sh',
-  'function-trace.sh',
   'eval-store.sh',
   'derivation-json.sh',
   'import-derivation.sh',
diff --git a/tests/functional2/eval/test_function_trace.py b/tests/functional2/eval/test_function_trace.py
new file mode 100644
index 000000000..55eed127a
--- /dev/null
+++ b/tests/functional2/eval/test_function_trace.py
@@ -0,0 +1,42 @@
+import pytest
+from testlib.fixtures.nix import Nix
+
+
+class TestFunctionTrace:
+    @pytest.fixture(autouse=True)
+    def setup(self, nix: Nix):
+        self.nix = nix
+
+    def call(self, expr: str) -> list[str]:
+        trace = (
+            self.nix.nix_instantiate(["--trace-function-calls", "--expr", expr]).run().stderr_plain
+        )
+        return [
+            " ".join(line.split(" ")[:-1])
+            for line in trace.splitlines()
+            if line.startswith("function-trace")
+        ]
+
+    def test_try_eval(self):
+        assert self.call('builtins.tryEval (throw "example")') == [
+            "function-trace entered «string»:1:1 at",
+            "function-trace entered «string»:1:19 at",
+            "function-trace exited «string»:1:19 at",
+            "function-trace exited «string»:1:1 at",
+        ]
+
+    @pytest.mark.parametrize(
+        "expr",
+        [
+            "({ x }: x) { }",
+            '({ x }: x) { x = "x"; y = "y"; }',
+            "(x: y: x + y) 1",
+            "(x: x) 1 2",
+            "1 2",
+        ],
+    )
+    def test_single_call(self, expr: str):
+        assert self.call(expr) == [
+            "function-trace entered «string»:1:1 at",
+            "function-trace exited «string»:1:1 at",
+        ]