Implement job id command

This cmomit also modifies run_external and job_unfreeze because the
engine_state stores the id of the current job in the
current_thread_job field, so its usages are accessed differently now.

crates/nu-command/src/default_context.rs

@@ -451,6 +451,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             JobSpawn,
             JobList,
             JobKill,
+            JobId,
             Job,
         };
 

crates/nu-command/src/experimental/job_id.rs

@@ -0,0 +1,54 @@
+use nu_engine::command_prelude::*;
+
+#[derive(Clone)]
+pub struct JobId;
+
+impl Command for JobId {
+    fn name(&self) -> &str {
+        "job id"
+    }
+
+    fn description(&self) -> &str {
+        "Get id of current job."
+    }
+
+    fn extra_description(&self) -> &str {
+        "This command returns the job id for the current background job. 
+The special id 0 indicates that this command was not called from a background job thread, and 
+was instead spawned by main nushell execution thread."
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("job id")
+            .category(Category::Experimental)
+            .input_output_types(vec![(Type::Nothing, Type::Int)])
+    }
+
+    fn search_terms(&self) -> Vec<&str> {
+        vec!["self", "this", "my-id", "this-id"]
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        _stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        let head = call.head;
+
+        if let Some((id, _)) = &engine_state.thread_job_entry {
+            Ok(Value::int(id.get() as i64, head).into_pipeline_data())
+        } else {
+            Ok(Value::int(0, head).into_pipeline_data())
+        }
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            example: "job id",
+            description: "Get id of current job",
+            result: None,
+        }]
+    }
+}

crates/nu-command/src/experimental/job_spawn.rs

@@ -69,8 +69,11 @@ impl Command for JobSpawn {
 
         let id = {
             let thread_job = ThreadJob::new(job_signals);
-            job_state.current_thread_job = Some(thread_job.clone());
-            jobs.add_job(Job::Thread(thread_job))
+            let id = jobs.add_job(Job::Thread(thread_job.clone()));
+
+            job_state.thread_job_entry = Some((id, thread_job));
+
+            id
         };
 
         let result = thread::Builder::new()

crates/nu-command/src/experimental/job_unfreeze.rs

@@ -115,7 +115,7 @@ fn unfreeze_job(
         Job::Frozen(FrozenJob { unfreeze: handle }) => {
             let pid = handle.pid();
 
-            if let Some(thread_job) = &state.current_thread_job {
+            if let Some(thread_job) = &state.current_thread_job() {
                 if !thread_job.try_add_pid(pid) {
                     kill_by_pid(pid.into()).map_err(|err| {
                         ShellError::Io(IoError::new_internal(
@@ -133,7 +133,7 @@ fn unfreeze_job(
                     .then(|| state.pipeline_externals_state.clone()),
             );
 
-            if let Some(thread_job) = &state.current_thread_job {
+            if let Some(thread_job) = &state.current_thread_job() {
                 thread_job.remove_pid(pid);
             }
 

crates/nu-command/src/experimental/mod.rs

@@ -1,5 +1,6 @@
 mod is_admin;
 mod job;
+mod job_id;
 mod job_kill;
 mod job_list;
 mod job_spawn;
@@ -9,9 +10,9 @@ mod job_unfreeze;
 
 pub use is_admin::IsAdmin;
 pub use job::Job;
+pub use job_id::JobId;
 pub use job_kill::JobKill;
 pub use job_list::JobList;
-
 pub use job_spawn::JobSpawn;
 
 #[cfg(all(unix, feature = "os"))]

crates/nu-command/src/system/run_external.rs

@@ -279,7 +279,7 @@ impl Command for External {
             )
         })?;
 
-        if let Some(thread_job) = &engine_state.current_thread_job {
+        if let Some(thread_job) = engine_state.current_thread_job() {
             if !thread_job.try_add_pid(child.pid()) {
                 kill_by_pid(child.pid().into()).map_err(|err| {
                     ShellError::Io(IoError::new_internal(
@@ -312,8 +312,8 @@ impl Command for External {
         }
 
         let jobs = engine_state.jobs.clone();
-        let this_job = engine_state.current_thread_job.clone();
         let is_interactive = engine_state.is_interactive;
+        let this_job = engine_state.current_thread_job().cloned();
         let child_pid = child.pid();
 
         // Wrap the output into a `PipelineData::ByteStream`.

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

@@ -8,9 +8,9 @@ use crate::{
     },
     eval_const::create_nu_constant,
     shell_error::io::IoError,
-    BlockId, Category, Config, DeclId, FileId, GetSpan, Handlers, HistoryConfig, Module, ModuleId,
-    OverlayId, ShellError, SignalAction, Signals, Signature, Span, SpanId, Type, Value, VarId,
-    VirtualPathId,
+    BlockId, Category, Config, DeclId, FileId, GetSpan, Handlers, HistoryConfig, JobId, Module,
+    ModuleId, OverlayId, ShellError, SignalAction, Signals, Signature, Span, SpanId, Type, Value,
+    VarId, VirtualPathId,
 };
 use fancy_regex::Regex;
 use lru::LruCache;
@@ -117,7 +117,7 @@ pub struct EngineState {
     pub jobs: Arc<Mutex<Jobs>>,
 
     // The job being executed with this engine state, or None if main thread
-    pub current_thread_job: Option<ThreadJob>,
+    pub thread_job_entry: Option<(JobId, ThreadJob)>,
 
     // When there are background jobs running, the interactive behavior of `exit` changes depending on
     // the value of this flag:
@@ -196,7 +196,7 @@ impl EngineState {
             is_debugging: IsDebugging::new(false),
             debugger: Arc::new(Mutex::new(Box::new(NoopDebugger))),
             jobs: Arc::new(Mutex::new(Jobs::default())),
-            current_thread_job: None,
+            thread_job_entry: None,
             exit_warning_given: Arc::new(AtomicBool::new(false)),
         }
     }
@@ -1080,7 +1080,12 @@ impl EngineState {
 
     // Determines whether the current state is being held by a background job
     pub fn is_background_job(&self) -> bool {
-        self.current_thread_job.is_some()
+        self.thread_job_entry.is_some()
+    }
+
+    // Gets the thread job entry
+    pub fn current_thread_job(&self) -> Option<&ThreadJob> {
+        self.thread_job_entry.as_ref().map(|(_, job)| job)
     }
 }