From 6e78cc90d3415694ec15bd273b47d21bb1be96ad Mon Sep 17 00:00:00 2001
From: Sergei Zimmerman <xokdvium@proton.me>
Date: Fri, 11 Jul 2025 20:20:48 +0300
Subject: [PATCH] libexpr: Fix invalid handling of errors for imported
 functions

c39cc004043b95d55a0c2c2bdba58d6d3e0db846 has added assertions for
all Value accesses and the following case has started failing with
an `unreachable`:

(/tmp/fun.nix):

```nix
{a}: a
```

```
$ nix eval --impure --expr 'import /tmp/fun.nix {a="a";b="b";}'
```

This would crash:

```
terminating due to unexpected unrecoverable internal error: Unexpected condition in getStorage at ../include/nix/expr/value.hh:844
```

This is not a regression, but rather surfaces an existing problem, which previously
was left undiagnosed. In the case of an import `fun` is the `import` primOp, so that read is invalid
and previously this resulted in an access into an inactive union member, which is UB.
The correct thing to use is `vCur`. Identical problem also affected the case of a missing argument.

Add previously failing test cases to the functional/lang test suite.

Fixes #13448.
---
 src/libexpr/eval.cc                                 |  4 ++--
 .../lang/eval-fail-missing-arg-import.err.exp       | 12 ++++++++++++
 .../lang/eval-fail-missing-arg-import.nix           |  1 +
 .../lang/eval-fail-undeclared-arg-import.err.exp    | 13 +++++++++++++
 .../lang/eval-fail-undeclared-arg-import.nix        |  4 ++++
 .../lang/non-eval-trivial-lambda-formals.nix        |  1 +
 6 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 tests/functional/lang/eval-fail-missing-arg-import.err.exp
 create mode 100644 tests/functional/lang/eval-fail-missing-arg-import.nix
 create mode 100644 tests/functional/lang/eval-fail-undeclared-arg-import.err.exp
 create mode 100644 tests/functional/lang/eval-fail-undeclared-arg-import.nix
 create mode 100644 tests/functional/lang/non-eval-trivial-lambda-formals.nix

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 1321e00a5..47cc35daa 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -1602,7 +1602,7 @@ void EvalState::callFunction(Value & fun, std::span<Value *> args, Value & vRes,
                                              symbols[i.name])
                                     .atPos(lambda.pos)
                                     .withTrace(pos, "from call site")
-                                    .withFrame(*fun.lambda().env, lambda)
+                                    .withFrame(*vCur.lambda().env, lambda)
                                     .debugThrow();
                         }
                         env2.values[displ++] = i.def->maybeThunk(*this, env2);
@@ -1629,7 +1629,7 @@ void EvalState::callFunction(Value & fun, std::span<Value *> args, Value & vRes,
                                 .atPos(lambda.pos)
                                 .withTrace(pos, "from call site")
                                 .withSuggestions(suggestions)
-                                .withFrame(*fun.lambda().env, lambda)
+                                .withFrame(*vCur.lambda().env, lambda)
                                 .debugThrow();
                         }
                     unreachable();
diff --git a/tests/functional/lang/eval-fail-missing-arg-import.err.exp b/tests/functional/lang/eval-fail-missing-arg-import.err.exp
new file mode 100644
index 000000000..45774f003
--- /dev/null
+++ b/tests/functional/lang/eval-fail-missing-arg-import.err.exp
@@ -0,0 +1,12 @@
+error:
+       … from call site
+         at /pwd/lang/eval-fail-missing-arg-import.nix:1:1:
+            1| import ./non-eval-trivial-lambda-formals.nix { }
+             | ^
+            2|
+
+       error: function 'anonymous lambda' called without required argument 'a'
+       at /pwd/lang/non-eval-trivial-lambda-formals.nix:1:1:
+            1| { a }: a
+             | ^
+            2|
diff --git a/tests/functional/lang/eval-fail-missing-arg-import.nix b/tests/functional/lang/eval-fail-missing-arg-import.nix
new file mode 100644
index 000000000..7cb33f2b5
--- /dev/null
+++ b/tests/functional/lang/eval-fail-missing-arg-import.nix
@@ -0,0 +1 @@
+import ./non-eval-trivial-lambda-formals.nix { }
diff --git a/tests/functional/lang/eval-fail-undeclared-arg-import.err.exp b/tests/functional/lang/eval-fail-undeclared-arg-import.err.exp
new file mode 100644
index 000000000..ca797d3ec
--- /dev/null
+++ b/tests/functional/lang/eval-fail-undeclared-arg-import.err.exp
@@ -0,0 +1,13 @@
+error:
+       … from call site
+         at /pwd/lang/eval-fail-undeclared-arg-import.nix:1:1:
+            1| import ./non-eval-trivial-lambda-formals.nix {
+             | ^
+            2|   a = "a";
+
+       error: function 'anonymous lambda' called with unexpected argument 'b'
+       at /pwd/lang/non-eval-trivial-lambda-formals.nix:1:1:
+            1| { a }: a
+             | ^
+            2|
+       Did you mean a?
diff --git a/tests/functional/lang/eval-fail-undeclared-arg-import.nix b/tests/functional/lang/eval-fail-undeclared-arg-import.nix
new file mode 100644
index 000000000..e8454c725
--- /dev/null
+++ b/tests/functional/lang/eval-fail-undeclared-arg-import.nix
@@ -0,0 +1,4 @@
+import ./non-eval-trivial-lambda-formals.nix {
+  a = "a";
+  b = "b";
+}
diff --git a/tests/functional/lang/non-eval-trivial-lambda-formals.nix b/tests/functional/lang/non-eval-trivial-lambda-formals.nix
new file mode 100644
index 000000000..46a7ea4f4
--- /dev/null
+++ b/tests/functional/lang/non-eval-trivial-lambda-formals.nix
@@ -0,0 +1 @@
+{ a }: a