fix(tvix/eval): Thunk `if` expr r/5090

Since the body of an `if` expr can refer to deferred upvalues, it needs
to be thunked so when we actually compile those deferred upvalues we
have something for the finalize op to point at. Without this all sorts
of weird things can happen due to the finalize op being run in the wrong
lambda context, up to and including a panic.

Change-Id: I040d5e1a7232fd841cfa4953539898fa49cbbb83
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6929
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI

1 files changed, 3 insertions, 1 deletions

diff --git a/tvix/eval/src/compiler/mod.rs b/tvix/eval/src/compiler/mod.rs
index cfb0ee64a6d8..fa08d626aaa3 100644
--- a/tvix/eval/src/compiler/mod.rs
+++ b/tvix/eval/src/compiler/mod.rs
@@ -212,7 +212,9 @@ impl Compiler<'_> {
             ast::Expr::Assert(assert) => {
                 self.thunk(slot, assert, move |c, s| c.compile_assert(s, assert))
             }
-            ast::Expr::IfElse(if_else) => self.compile_if_else(slot, if_else),
+            ast::Expr::IfElse(if_else) => {
+                self.thunk(slot, if_else, move |c, s| c.compile_if_else(s, if_else))
+            }
             ast::Expr::LetIn(let_in) => self.compile_let_in(slot, let_in),
             ast::Expr::Ident(ident) => self.compile_ident(slot, ident),
             ast::Expr::With(with) => self.thunk(slot, with, |c, s| c.compile_with(s, with)),