Add cast debug output (#3767)

<!-- Reference any GitHub issues resolved by this PR -->

Closes #3207
Closes #2879

## Introduced changes

<!-- A brief description of the changes -->

- Added support for logging in `sncast`. Currently no logs are emitted
by cast itself but various dependencies, like starknet-rs emit them, and
now they can be displayed by providing `SNCAST_LOG={trace level}`

## Checklist

<!-- Make sure all of these are complete -->

- [x] Linked relevant issue
- [x] Updated relevant documentation
- [x] Added relevant tests
- [x] Performed self-review of the code
- [x] Added changes to `CHANGELOG.md`

Author: cptartur

CHANGELOG.md

@@ -13,6 +13,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Updated the error message returned when calling a nonexistent method on a contract to better align with the format used by the network
 
+### Cast
+
+#### Added
+
+- Debug logging for `sncast` commands that can be enabled by setting `CAST_LOG` env variable.
+
 ## [0.50.0] - 2025-09-29
 
 ### Forge

Cargo.lock

@@ -125,3 +125,4 @@ chrono = "0.4.41"
 tracing-subscriber = { version = "0.3.20", features = ["env-filter"] }
 tracing = "0.1.41"
 tracing-chrome = "0.7.2"
+tracing-log = "0.2.0"

Cargo.toml

@@ -58,6 +58,9 @@ toml_edit.workspace = true
 num-traits.workspace = true
 foundry-ui = { path = "../foundry-ui" }
 universal-sierra-compiler-api = { path = "../universal-sierra-compiler-api" }
+tracing-subscriber.workspace = true
+tracing.workspace = true
+tracing-log.workspace = true
 
 [dev-dependencies]
 ctor.workspace = true

crates/sncast/Cargo.toml

@@ -211,7 +211,35 @@ impl From<DeployArguments> for Arguments {
     }
 }
 
+fn init_logging() {
+    use std::io;
+    use std::io::IsTerminal;
+    use tracing_log::LogTracer;
+    use tracing_subscriber::filter::{EnvFilter, LevelFilter};
+    use tracing_subscriber::fmt::Layer;
+    use tracing_subscriber::fmt::time::Uptime;
+    use tracing_subscriber::prelude::*;
+
+    let fmt_layer = Layer::new()
+        .with_writer(io::stderr)
+        .with_ansi(io::stderr().is_terminal())
+        .with_timer(Uptime::default())
+        .with_filter(
+            EnvFilter::builder()
+                .with_default_directive(LevelFilter::WARN.into())
+                .with_env_var("SNCAST_LOG")
+                .from_env_lossy(),
+        );
+
+    LogTracer::init().expect("could not initialize log tracer");
+
+    tracing::subscriber::set_global_default(tracing_subscriber::registry().with(fmt_layer))
+        .expect("could not set up global logger");
+}
+
 fn main() -> Result<()> {
+    init_logging();
+
     let cli = Cli::parse();
 
     let output_format = output_format_from_json_flag(cli.json);

crates/sncast/src/main.rs

@@ -59,6 +59,7 @@
 * [Verifying Contracts](starknet/verify.md)
 * [Calldata Transformation](starknet/calldata-transformation.md)
 * [Block Explorers](starknet/block_explorer.md)
+* [Developer Functionalites](starknet/developer.md)
 
 ---
 

docs/src/SUMMARY.md

@@ -0,0 +1,20 @@
+# Developer Functionalities
+
+## Logging
+
+`sncast` supports emitting logs, including the logs from the requests sent to the network.
+Logs can be enabled by setting `SNCAST_LOG` environment variable to desired log level.
+
+For example, to enable logs with level `debug` and higher, run:
+
+```shell
+$ SNCAST_LOG="debug" sncast ...
+```
+
+Additional filtering can be set to the `SNCAST_LOG` environment variable,
+see [tracing-subscriber](https://docs.rs/tracing-subscriber/0.3.20/tracing_subscriber/filter/struct.EnvFilter.html#directives)
+documentation for more details.
+
+> ⚠️ **Warning**
+>
+> Logs can expose sensitive information, such as private keys. Never use logging in production environments.