fix(tvix/eval): wrap asserts in a thunk

As the new test case demonstrates, asserts need to be evaluated lazily.

Change-Id: I808046722c5a504e9497855ca5026d255c7a4c34
Reviewed-on: https://cl.tvl.fyi/c/depot/+/6494
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: sterni <sternenseemann@systemli.org>

tvix/eval/src/compiler/mod.rs

@@ -168,7 +168,9 @@ impl Compiler<'_, '_> {
                 c.compile_select(s, sel.clone())
             }),
 
-            ast::Expr::Assert(assert) => self.compile_assert(slot, assert),
+            ast::Expr::Assert(assert) => {
+                self.thunk(slot, &assert, move |c, a, s| c.compile_assert(s, a.clone()))
+            }
             ast::Expr::IfElse(if_else) => self.compile_if_else(slot, if_else),
             ast::Expr::LetIn(let_in) => self.compile_let_in(slot, let_in),
             ast::Expr::Ident(ident) => self.compile_ident(slot, ident),