feat(tvix/repl): Allow binding variables at the top-level r/8346

Allow binding variables at the REPL's toplevel in the same way the Nix
REPL does, using the syntax <ident> = <expr>. This fully, strictly
evaluates the value and sets it in the repl's "env", which gets passed
in at the toplevel when evaluating expressions.

The laziness behavior differs from Nix's, but I think this is good:

    ❯ nix repl
    Welcome to Nix version 2.3.18. Type :? for help.

    nix-repl> x = builtins.trace "x" 1

    nix-repl> x
    trace: x
    1

    nix-repl> x
    1

vs tvix:

    tvix-repl> x = builtins.trace "x" 1
    trace: "x" :: string
    tvix-repl> x
    => 1 :: int
    tvix-repl> x
    => 1 :: int

Bug: https://b.tvl.fyi/issues/371
Change-Id: Ieb2d626b7195fa87be638c9a4dae2eee45eb9ab1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11954
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Autosubmit: aspen <root@gws.fyi>

1 files changed, 2 insertions, 0 deletions

diff --git a/tvix/cli/Cargo.toml b/tvix/cli/Cargo.toml
index 644393a7c4ed..f6d03ce5ab8f 100644
--- a/tvix/cli/Cargo.toml
+++ b/tvix/cli/Cargo.toml
@@ -20,6 +20,8 @@ clap = { version = "4.0", features = ["derive", "env"] }
 dirs = "4.0.0"
 rustyline = "10.0.0"
 rnix = "0.11.0"
+rowan = "*"
+smol_str = "0.2.0"
 thiserror = "1.0.38"
 tokio = "1.28.0"
 tracing = "0.1.40"