From 3aa73c21e3afc91522a6121b0d591af6925b4ba6 Mon Sep 17 00:00:00 2001
From: Rodrigo Arias Mallo <rodarima@gmail.com>
Date: Mon, 13 Oct 2025 16:05:30 +0200
Subject: [PATCH] Add builtins.catchAll to catch all types of errors

Allows fetching multiple Git repositories with builtin.fetchGit and
catching any errors thrown by the builtin, in opposition to the builtin
tryEval.
---
 src/libexpr/primops.cc | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index 36a67a39d..3b26f9f43 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -849,6 +849,44 @@ static RegisterPrimOp primop_tryEval({
     .fun = prim_tryEval,
 });
 
+/* Like tryEval but catch all errors. Success => {success=true; value=something;},
+ * else => {success=false; value=false;} */
+static void prim_catchAll(EvalState & state, const PosIdx pos, Value * * args, Value & v)
+{
+    auto attrs = state.buildBindings(3);
+    try {
+        state.forceValue(*args[0], pos);
+        attrs.insert(state.sValue, args[0]);
+        attrs.alloc("success").mkBool(true);
+        attrs.alloc("msg").mkNull();
+    } catch (Error & e) {
+        attrs.alloc(state.sValue).mkBool(false);
+        attrs.alloc("success").mkBool(false);
+        attrs.alloc("msg").mkString(e.msg());
+    }
+    v.mkAttrs(attrs);
+}
+
+static RegisterPrimOp primop_catchAll({
+    .name = "__catchAll",
+    .args = {"e"},
+    .doc = R"(
+      Try to shallowly evaluate *e*. Return a set containing the
+      attributes `success` (`true` if *e* evaluated successfully,
+      `false` if an error was thrown) and `value`, equalling *e* if
+      successful and `false` otherwise. In contrast with `tryEval`,
+      `catchAll` will prevent all errors from being thrown, including
+      for those created by `abort` and type errors generated by
+      builtins. Also note that this doesn't evaluate *e* deeply, so
+      `let e = { x = throw ""; }; in (builtins.catchAll e).success`
+      will be `true`. Using `builtins.deepSeq` one can get the expected
+      result: `let e = { x = throw ""; }; in
+      (builtins.catchAll (builtins.deepSeq e e)).success` will be
+      `false`.
+    )",
+    .fun = prim_catchAll,
+});
+
 /* Return an environment variable.  Use with care. */
 static void prim_getEnv(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
-- 
2.51.0