lib: automatic title: replace fg with description from jobs (#7982)

* Automatic title: Replace fg with description from jobs

* Avoid error messages when there is no job

* Use $jobstates and $jobtexts to look for jobs

`jobs %string` doesn't work correctly when run inside `$()`. `$jobstates` and
`$jobtexts` is available in the current shell process, so even though we need
to replicate a bit more logic, every type of `fg` invocation works correctly.

* lib: clean up termsupport.zsh
Co-authored-by: Marc Cornellà <marc.cornella@live.com>

lib/termsupport.zsh

@@ -50,22 +50,52 @@ fi
 
 # Runs before showing the prompt
 function omz_termsupport_precmd {
-  emulate -L zsh
-
-  if [[ "$DISABLE_AUTO_TITLE" == true ]]; then
-    return
-  fi
-
+  [[ "$DISABLE_AUTO_TITLE" == true ]] && return
   title $ZSH_THEME_TERM_TAB_TITLE_IDLE $ZSH_THEME_TERM_TITLE_IDLE
 }
 
 # Runs before executing the command
 function omz_termsupport_preexec {
+  [[ "$DISABLE_AUTO_TITLE" == true ]] && return
+
   emulate -L zsh
   setopt extended_glob
 
-  if [[ "$DISABLE_AUTO_TITLE" == true ]]; then
-    return
+  # split command into array of arguments
+  local -a cmdargs
+  cmdargs=("${(z)2}")
+  # if running fg, extract the command from the job description
+  if [[ "${cmdargs[1]}" = fg ]]; then
+    # get the job id from the first argument passed to the fg command
+    local job_id jobspec="${cmdargs[2]#%}"
+    # logic based on jobs arguments:
+    # http://zsh.sourceforge.net/Doc/Release/Jobs-_0026-Signals.html#Jobs
+    # https://www.zsh.org/mla/users/2007/msg00704.html
+    case "$jobspec" in
+      <->) # %number argument:
+        # use the same <number> passed as an argument
+        job_id=${jobspec} ;;
+      ""|%|+) # empty, %% or %+ argument:
+        # use the current job, which appears with a + in $jobstates:
+        # suspended:+:5071=suspended (tty output)
+        job_id=${(k)jobstates[(r)*:+:*]} ;;
+      -) # %- argument:
+        # use the previous job, which appears with a - in $jobstates:
+        # suspended:-:6493=suspended (signal)
+        job_id=${(k)jobstates[(r)*:-:*]} ;;
+      [?]*) # %?string argument:
+        # use $jobtexts to match for a job whose command *contains* <string>
+        job_id=${(k)jobtexts[(r)*${(Q)jobspec}*]} ;;
+      *) # %string argument:
+        # use $jobtexts to match for a job whose command *starts with* <string>
+        job_id=${(k)jobtexts[(r)${(Q)jobspec}*]} ;;
+    esac
+
+    # override preexec function arguments with job command
+    if [[ -n "${jobtexts[$job_id]}" ]]; then
+      1="${jobtexts[$job_id]}"
+      2="${jobtexts[$job_id]}"
+    fi
   fi
 
   # cmd name only, or if this is sudo or ssh, the next cmd