49906 (Bart), 49911: Fixes to querying jobs in subshell.

Don't attempt to query invalid job off end of table, resulting in
crashes from $jobtstates.

If background task started in subshell, look at tatsks within subshell
instead of main shell.  Document and add test.

ChangeLog

@@ -1,3 +1,11 @@
+2022-03-30  Peter Stephenson  <p.stephenson@samsung.com>
+
+	* 49906 (Bart), 49911: Doc/Zsh/builtins.yo,
+	Doc/Zsh/mod_parameter.yo, Src/exec.c, Src/jobs.c,
+	Test/W03jobparameters.ztst: Fix querying jobs in subshell.
+	Don't uery invalid job at end, if background job started in
+	subshell query jobs in subshell instead of main shell.
+
 2022-03-30  Mikael Magnusson  <mikachu@gmail.com>
 
 	* 49893: Src/Zle/comp.h, Src/Zle/compcore.c: Fix comments for

Doc/Zsh/builtins.yo

@@ -1114,6 +1114,24 @@ The tt(-Z) option replaces the shell's argument and environment space with
 the given string, truncated if necessary to fit.  This will normally be
 visible in tt(ps) (manref(ps)(1)) listings.  This feature is typically
 used by daemons, to indicate their state.
+
+Full job control is only available in the top-level interactive shell,
+not in commands run in the left hand side of pipelines or within
+the tt(LPAR())var(...)tt(RPAR()) construct.  However, a snapshot
+of the job state at that point is taken, so it is still possible
+to use the tt(jobs) builtin, or any parameter providing job information.
+This gives information about the state of jobs at the point the subshell
+was created.  If background processes are created within the subshell,
+then instead information about those processes is provided.
+
+For example,
+
+example(sleep 10 &    # Job in background
+LPAR()             # Shell forks
+jobs          # Shows information about "sleep 10 &"
+sleep 5 &     # Process in background (no job control)
+jobs          # Shows information about "sleep 5 &"
+RPAR())
 )
 findex(kill)
 cindex(killing jobs)

Doc/Zsh/mod_parameter.yo

@@ -165,6 +165,8 @@ The keys of the associative arrays are usually valid job numbers,
 and these are the values output with, for example, tt(${(k)jobdirs}).
 Non-numeric job references may be used when looking up a value;
 for example, tt(${jobdirs[%+]}) refers to the current job.
+
+See the tt(jobs) builtin for how job information is provided in a subshell.
 )
 vindex(jobtexts)
 item(tt(jobtexts))(
@@ -173,6 +175,8 @@ that were used to start the jobs.
 
 Handling of the keys of the associative array is as described for
 tt(jobdirs) above.
+
+See the tt(jobs) builtin for how job information is provided in a subshell.
 )
 vindex(jobstates)
 item(tt(jobstates))(
@@ -189,6 +193,8 @@ the var(state) describes the state of that process.
 
 Handling of the keys of the associative array is as described for
 tt(jobdirs) above.
+
+See the tt(jobs) builtin for how job information is provided in a subshell.
 )
 vindex(nameddirs)
 item(tt(nameddirs))(

Src/exec.c

@@ -1689,6 +1689,7 @@ execpline(Estate state, wordcode slcode, int how, int last1)
     execpline2(state, code, how, opipe[0], ipipe[1], last1);
     pline_level--;
     if (how & Z_ASYNC) {
+	clearoldjobtab();
 	lastwj = newjob;
 
         if (thisjob == list_pipe_job)

Src/jobs.c

@@ -1718,8 +1718,15 @@ clearjobtab(int monitor)
 	/* Don't report any job we're part of */
 	if (thisjob != -1 && thisjob < oldmaxjob)
 	    memset(oldjobtab+thisjob, 0, sizeof(struct job));
+
+	/* oldmaxjob is now the size of the table, but outside
+	 * this function, it's used as a job number, which must
+	 * be the largest index available in the table.
+	 */
+	--oldmaxjob;
     }
 
+
     memset(jobtab, 0, jobtabsize * sizeof(struct job)); /* zero out table */
     maxjob = 0;
 
@@ -1733,6 +1740,18 @@ clearjobtab(int monitor)
     thisjob = initjob();
 }
 
+/* In a subshell, decide we want our own job table after all. */
+
+/**/
+mod_export void
+clearoldjobtab(void)
+{
+    if (oldjobtab)
+	free(oldjobtab);
+    oldjobtab = NULL;
+    oldmaxjob = 0;
+}
+
 static int initnewjob(int i)
 {
     jobtab[i].stat = STAT_INUSE;
@@ -2449,6 +2468,7 @@ bin_fg(char *name, char **argv, Options ops, int func)
 	case BIN_BG:
 	case BIN_WAIT:
 	    if (func == BIN_BG) {
+		clearoldjobtab();
 		jobtab[job].stat |= STAT_NOSTTY;
 		jobtab[job].stat &= ~STAT_CURSH;
 	    }

Test/W03jobparameters.ztst

@@ -48,3 +48,31 @@
 *>running:+:*=running
 *>running:+:*=running
 *>zsh:*SIGHUPed*
+
+# $jobstates refers to a job started in the main shell unless
+# one has been started in the subshell.  In the latter case,
+# the subshell has no job control so the job is not marked as current.
+  zpty_start
+  zpty_input "MODULE_PATH=${(q)MODULE_PATH}"
+  zpty_input 'sleep 3 &'
+  zpty_input '(print main; print $jobstates; sleep 2& print sub; print $jobstates)'
+  zpty_input 'jobs -s'
+  zpty_stop
+0:$jobstate shows one job started in main shell or one started in subshell
+*>\[1] [0-9]##
+>main
+*>running:+:*=running
+>sub
+*>running::*=running
+*>zsh:*SIGHUPed*
+
+# output from zpty removes empty lines
+  zpty_start
+  zpty_input "MODULE_PATH=${(q)MODULE_PATH}"
+  zpty_input '(print main; print $jobstates; sleep 2& print sub; print $jobstates)'
+  zpty_input 'jobs -s'
+  zpty_stop
+0:$jobstate shows no job started in main shell but one started in subshell
+>main
+>sub
+*>running::*=running