Add job tags (#15555)

# Description

This PR implements job tagging through the usage of a new `job tag`
command and a `--tag` for `job spawn`

Closes #15354

# User-Facing Changes

- New `job tag` command
- Job list may now have an additional `tag` column for the tag of jobs
(rows representing jobs without tags do not have this column filled)
- New `--tag` flag for `job spawn`

# Tests + Formatting

Integration tests are provided to test the newly implemented features

# After Submitting

Possibly document job tagging in the jobs documentation

crates/nu-protocol/src/engine/jobs.rs

@@ -38,6 +38,10 @@ impl Jobs {
         self.jobs.get(&id)
     }
 
+    pub fn lookup_mut(&mut self, id: JobId) -> Option<&mut Job> {
+        self.jobs.get_mut(&id)
+    }
+
     pub fn remove_job(&mut self, id: JobId) -> Option<Job> {
         if self.last_frozen_job_id.is_some_and(|last| id == last) {
             self.last_frozen_job_id = None;
@@ -134,13 +138,15 @@ pub enum Job {
 pub struct ThreadJob {
     signals: Signals,
     pids: Arc<Mutex<HashSet<u32>>>,
+    tag: Option<String>,
 }
 
 impl ThreadJob {
-    pub fn new(signals: Signals) -> Self {
+    pub fn new(signals: Signals, tag: Option<String>) -> Self {
         ThreadJob {
             signals,
             pids: Arc::new(Mutex::new(HashSet::default())),
+            tag,
         }
     }
 
@@ -197,10 +203,25 @@ impl Job {
             Job::Frozen(frozen_job) => frozen_job.kill(),
         }
     }
+
+    pub fn tag(&self) -> Option<&String> {
+        match self {
+            Job::Thread(thread_job) => thread_job.tag.as_ref(),
+            Job::Frozen(frozen_job) => frozen_job.tag.as_ref(),
+        }
+    }
+
+    pub fn assign_tag(&mut self, tag: Option<String>) {
+        match self {
+            Job::Thread(thread_job) => thread_job.tag = tag,
+            Job::Frozen(frozen_job) => frozen_job.tag = tag,
+        }
+    }
 }
 
 pub struct FrozenJob {
     pub unfreeze: UnfreezeHandle,
+    pub tag: Option<String>,
 }
 
 impl FrozenJob {

crates/nu-protocol/src/process/child.rs

@@ -182,12 +182,18 @@ impl PostWaitCallback {
         PostWaitCallback(Box::new(f))
     }
 
-    /// Creates a PostWaitCallback that checks creates a frozen job in the job table
+    /// Creates a PostWaitCallback that creates a frozen job in the job table
     /// if the incoming wait status indicates that the job was frozen.
     ///
     /// If `child_pid` is provided, the returned callback will also remove
     /// it from the pid list of the current running job.
-    pub fn for_job_control(engine_state: &EngineState, child_pid: Option<u32>) -> Self {
+    ///
+    /// The given `tag` argument will be used as the tag for the newly created job table entry.
+    pub fn for_job_control(
+        engine_state: &EngineState,
+        child_pid: Option<u32>,
+        tag: Option<String>,
+    ) -> Self {
         let this_job = engine_state.current_thread_job.clone();
         let jobs = engine_state.jobs.clone();
         let is_interactive = engine_state.is_interactive;
@@ -200,7 +206,7 @@ impl PostWaitCallback {
             if let ForegroundWaitStatus::Frozen(unfreeze) = status {
                 let mut jobs = jobs.lock().expect("jobs lock is poisoned!");
 
-                let job_id = jobs.add_job(Job::Frozen(FrozenJob { unfreeze }));
+                let job_id = jobs.add_job(Job::Frozen(FrozenJob { unfreeze, tag }));
 
                 if is_interactive {
                     println!("\nJob {} is frozen", job_id.get());