feat(forge fmt): add watch mode (foundry-rs#9838)

* feat(forge): add watch mode to forge fmt

* keen fmt run sync

Author: PanGan21

crates/forge/bin/cmd/fmt.rs

@@ -1,3 +1,4 @@
+use super::watch::WatchArgs;
 use clap::{Parser, ValueHint};
 use eyre::{Context, Result};
 use forge_fmt::{format_to, parse};
@@ -39,6 +40,9 @@ pub struct FmtArgs {
     /// In 'check' and stdin modes, outputs raw formatted code instead of the diff.
     #[arg(long, short)]
     raw: bool,
+
+    #[command(flatten)]
+    pub watch: WatchArgs,
 }
 
 impl_figment_convert_basic!(FmtArgs);
@@ -186,6 +190,11 @@ impl FmtArgs {
 
         Ok(())
     }
+
+    /// Returns whether `FmtArgs` was configured with `--watch`
+    pub fn is_watch(&self) -> bool {
+        self.watch.watch.is_some()
+    }
 }
 
 struct Line(Option<usize>);

crates/forge/bin/cmd/watch.rs

@@ -1,6 +1,6 @@
 use super::{
-    build::BuildArgs, coverage::CoverageArgs, doc::DocArgs, snapshot::GasSnapshotArgs,
-    test::TestArgs,
+    build::BuildArgs, coverage::CoverageArgs, doc::DocArgs, fmt::FmtArgs,
+    snapshot::GasSnapshotArgs, test::TestArgs,
 };
 use alloy_primitives::map::HashSet;
 use clap::Parser;
@@ -325,6 +325,14 @@ pub async fn watch_coverage(args: CoverageArgs) -> Result<()> {
     run(config).await
 }
 
+pub async fn watch_fmt(args: FmtArgs) -> Result<()> {
+    let config = args.watch.watchexec_config(|| {
+        let config = args.load_config()?;
+        Ok([config.src, config.test, config.script])
+    })?;
+    run(config).await
+}
+
 /// Executes a [`Watchexec`] that listens for changes in the project's sources directory
 pub async fn watch_doc(args: DocArgs) -> Result<()> {
     let config = args.watch.watchexec_config(|| {

crates/forge/bin/main.rs

@@ -104,7 +104,13 @@ fn run() -> Result<()> {
                 utils::block_on(cmd.run())
             }
         }
-        ForgeSubcommand::Fmt(cmd) => cmd.run(),
+        ForgeSubcommand::Fmt(cmd) => {
+            if cmd.is_watch() {
+                utils::block_on(watch::watch_fmt(cmd))
+            } else {
+                cmd.run()
+            }
+        }
         ForgeSubcommand::Config(cmd) => cmd.run(),
         ForgeSubcommand::Flatten(cmd) => cmd.run(),
         ForgeSubcommand::Inspect(cmd) => cmd.run(),