Add changes-since command to eden notify subcommand

Summary:
# Context

We are introducing EdenFS notifications to support scalable and ergonomic file system notifications for EdenFS mounts.

# This Diff

Adds a new command (`changes-since`) to the `eden nofity` subcommand. This command will return all of the changes since the provided position for the given mount.

# Technical Details

Added new module for changes since command that does nothing - yet

# Next Steps

Implement the `changes-since` command to `eden notify` then iterate on the `streamChangesSinceV2` Thrift endpoint.

# Discussion Points

None

Differential Revision: D65774220

fbshipit-source-id: 0ef4005345c5c5f8ab7dd50c599371b259b4ec84

eden/fs/cli_rs/edenfs-commands/src/notify.rs

@@ -14,6 +14,7 @@ use clap::Parser;
 use crate::ExitCode;
 use crate::Subcommand;
 
+mod changes_since;
 mod get_position;
 
 #[derive(Parser, Debug)]
@@ -26,6 +27,7 @@ pub struct NotifyCmd {
 #[derive(Parser, Debug)]
 pub enum NotifySubcommand {
     GetPosition(get_position::GetPositionCmd),
+    ChangesSince(changes_since::ChangesSinceCmd),
 }
 
 #[async_trait]
@@ -34,6 +36,7 @@ impl Subcommand for NotifyCmd {
         use NotifySubcommand::*;
         let sc: &(dyn Subcommand + Send + Sync) = match &self.subcommand {
             GetPosition(cmd) => cmd,
+            ChangesSince(cmd) => cmd,
         };
         sc.run().await
     }

eden/fs/cli_rs/edenfs-commands/src/notify/changes_since.rs

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This software may be used and distributed according to the terms of the
+ * GNU General Public License version 2.
+ */
+
+//! edenfsctl notify changes-since
+
+use std::path::PathBuf;
+
+use anyhow::anyhow;
+use anyhow::Context;
+use anyhow::Result;
+use async_trait::async_trait;
+use clap::Parser;
+use edenfs_client::EdenFsInstance;
+use edenfs_utils::bytes_from_path;
+use hg_util::path::expand_path;
+
+use crate::util::locate_repo_root;
+use crate::ExitCode;
+
+// TODO: add a --json flag to print the output in JSON format
+#[derive(Parser, Debug)]
+#[clap(about = "Returns the changes since the given EdenFS journal position")]
+pub struct ChangesSinceCmd {
+    #[clap(parse(from_str = expand_path))]
+    /// Path to the mount point
+    mount_point: Option<PathBuf>,
+}
+
+impl ChangesSinceCmd {
+    fn get_mount_point(&self) -> Result<PathBuf> {
+        if let Some(path) = &self.mount_point {
+            Ok(path.clone())
+        } else {
+            locate_repo_root(
+                &std::env::current_dir().context("Unable to retrieve current working directory")?,
+            )
+            .map(|p| p.to_path_buf())
+            .ok_or_else(|| anyhow!("Unable to locate repository root"))
+        }
+    }
+}
+
+#[async_trait]
+impl crate::Subcommand for ChangesSinceCmd {
+    #[cfg(not(fbcode_build))]
+    async fn run(&self) -> Result<ExitCode> {
+        eprintln!("not supported in non-fbcode build");
+        Ok(1)
+    }
+
+    #[cfg(fbcode_build)]
+    async fn run(&self) -> Result<ExitCode> {
+        let instance = EdenFsInstance::global();
+        let _client = instance.connect(None).await?;
+        let mount_point_path = self.get_mount_point()?;
+        let _mount_point = bytes_from_path(mount_point_path)?;
+
+        Ok(0)
+    }
+}