test(tvix/cli): Make the REPL testable

Juggle around the internals of the tvix-cli crate so that we expose the
Repl as a public type with a `send` method, that sends a string to the
repl and *captures all output* so that it can be subsequently asserted
on in tests. Then, demonstrate that this works with a single (for now)
REPL test using expect-test to assert on the output of a single command
sent to the REPL.

As the REPL gets more complicated, this will allow us to make tests that
cover that complex behavior.

Change-Id: I88175bd72d8760c79faade95ebb1d956f08a7b83
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11958
Autosubmit: aspen <root@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/cli/src/args.rs

@@ -0,0 +1,72 @@
+use std::path::PathBuf;
+
+use clap::Parser;
+use tracing::Level;
+
+#[derive(Parser, Clone)]
+pub struct Args {
+    /// A global log level to use when printing logs.
+    /// It's also possible to set `RUST_LOG` according to
+    /// `tracing_subscriber::filter::EnvFilter`, which will always have
+    /// priority.
+    #[arg(long, default_value_t=Level::INFO)]
+    pub log_level: Level,
+
+    /// Path to a script to evaluate
+    pub script: Option<PathBuf>,
+
+    #[clap(long, short = 'E')]
+    pub expr: Option<String>,
+
+    /// Dump the raw AST to stdout before interpreting
+    #[clap(long, env = "TVIX_DISPLAY_AST")]
+    pub display_ast: bool,
+
+    /// Dump the bytecode to stdout before evaluating
+    #[clap(long, env = "TVIX_DUMP_BYTECODE")]
+    pub dump_bytecode: bool,
+
+    /// Trace the runtime of the VM
+    #[clap(long, env = "TVIX_TRACE_RUNTIME")]
+    pub trace_runtime: bool,
+
+    /// Capture the time (relative to the start time of evaluation) of all events traced with
+    /// `--trace-runtime`
+    #[clap(long, env = "TVIX_TRACE_RUNTIME_TIMING", requires("trace_runtime"))]
+    pub trace_runtime_timing: bool,
+
+    /// Only compile, but do not execute code. This will make Tvix act
+    /// sort of like a linter.
+    #[clap(long)]
+    pub compile_only: bool,
+
+    /// Don't print warnings.
+    #[clap(long)]
+    pub no_warnings: bool,
+
+    /// A colon-separated list of directories to use to resolve `<...>`-style paths
+    #[clap(long, short = 'I', env = "NIX_PATH")]
+    pub nix_search_path: Option<String>,
+
+    /// Print "raw" (unquoted) output.
+    #[clap(long)]
+    pub raw: bool,
+
+    /// Strictly evaluate values, traversing them and forcing e.g.
+    /// elements of lists and attribute sets before printing the
+    /// return value.
+    #[clap(long)]
+    pub strict: bool,
+
+    #[arg(long, env, default_value = "memory://")]
+    pub blob_service_addr: String,
+
+    #[arg(long, env, default_value = "memory://")]
+    pub directory_service_addr: String,
+
+    #[arg(long, env, default_value = "memory://")]
+    pub path_info_service_addr: String,
+
+    #[arg(long, env, default_value = "dummy://")]
+    pub build_service_addr: String,
+}