Show the reason why a join request was declined

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

crates/project/Cargo.toml

@@ -45,6 +45,7 @@ serde_json = { version = "1.0.64", features = ["preserve_order"] }
 sha2 = "0.10"
 similar = "1.3"
 smol = "1.2.5"
+thiserror = "1.0.29"
 toml = "0.5"
 
 [dev-dependencies]

crates/project/src/project.rs

@@ -49,6 +49,7 @@ use std::{
     },
     time::Instant,
 };
+use thiserror::Error;
 use util::{post_inc, ResultExt, TryFutureExt as _};
 
 pub use fs::*;
@@ -90,6 +91,18 @@ pub struct Project {
     nonce: u128,
 }
 
+#[derive(Error, Debug)]
+pub enum JoinProjectError {
+    #[error("host declined join request")]
+    HostDeclined,
+    #[error("host closed the project")]
+    HostClosedProject,
+    #[error("host went offline")]
+    HostWentOffline,
+    #[error("{0}")]
+    Other(#[from] anyhow::Error),
+}
+
 enum OpenBuffer {
     Strong(ModelHandle<Buffer>),
     Weak(WeakModelHandle<Buffer>),
@@ -356,7 +369,7 @@ impl Project {
         languages: Arc<LanguageRegistry>,
         fs: Arc<dyn Fs>,
         cx: &mut AsyncAppContext,
-    ) -> Result<ModelHandle<Self>> {
+    ) -> Result<ModelHandle<Self>, JoinProjectError> {
         client.authenticate_and_connect(true, &cx).await?;
 
         let response = client
@@ -367,7 +380,20 @@ impl Project {
 
         let response = match response.variant.ok_or_else(|| anyhow!("missing variant"))? {
             proto::join_project_response::Variant::Accept(response) => response,
-            proto::join_project_response::Variant::Decline(_) => Err(anyhow!("rejected"))?,
+            proto::join_project_response::Variant::Decline(decline) => {
+                match proto::join_project_response::decline::Reason::from_i32(decline.reason) {
+                    Some(proto::join_project_response::decline::Reason::Declined) => {
+                        Err(JoinProjectError::HostDeclined)?
+                    }
+                    Some(proto::join_project_response::decline::Reason::Closed) => {
+                        Err(JoinProjectError::HostClosedProject)?
+                    }
+                    Some(proto::join_project_response::decline::Reason::WentOffline) => {
+                        Err(JoinProjectError::HostWentOffline)?
+                    }
+                    None => Err(anyhow!("missing decline reason"))?,
+                }
+            }
         };
 
         let replica_id = response.replica_id as ReplicaId;