Support for grabbing multiple outputs in swank:eval-and-grab-output

It is often desirable to get output from time and trace in Emacs,
particularly in org-babel.  This patch extends
swank:eval-and-grab-output to support emitting *trace-output*; it also
introduces *error-output*, for good measure.

We check whether eval-and-grab-output caller presumes older interface
to it and return a legacy list of two elements instead of alist in
those cases.

This check can very likely be dropped when either Emacs 27 or Org 9.4
become unsupported.

slime.el

@@ -4058,22 +4058,39 @@ inserted in the current buffer."
      (run-hooks 'slime-transcript-stop-hook)
      (message "Evaluation aborted on %s." condition))))
 
-(defun slime-eval-print (string)
-  "Eval STRING in Lisp; insert any output and the result at point."
-  (slime-eval-async `(swank:eval-and-grab-output ,string)
-    (lambda (result)
-      (cl-destructuring-bind (output value) result
-        (push-mark)
-        (insert output value)))))
-
-(defun slime-eval-save (string)
-  "Evaluate STRING in Lisp and save the result in the kill ring."
-  (slime-eval-async `(swank:eval-and-grab-output ,string)
-    (lambda (result)
-      (cl-destructuring-bind (output value) result
-        (let ((string (concat output value)))
-          (kill-new string)
-          (message "Evaluation finished; pushed result to kill ring."))))))
+(defconst slime-output-targets
+  '(common-lisp:values
+    common-lisp:*standard-output*
+    common-lisp:*trace-output*
+    common-lisp:*error-output*)
+  "Possible keys in the alist returned by Common Lisp function `swank:eval-and-grab-output'.")
+
+(cl-defun slime-eval-print
+    (string &optional (targets-to-print '(common-lisp:*standard-output*
+                                          common-lisp:values)))
+  "Eval STRING in Lisp; insert standard output and the result at point.
+
+Contents to be inserted may be specified via optional parameter TARGETS-TO-PRINT which should be a (multi)subset of list `slime-output-targets'."
+  (cl-assert (null (cl-set-difference targets-to-print slime-output-targets)))
+  (slime-eval-async `(swank:eval-and-grab-output ,string ',targets-to-print)
+    (lambda (results-alist)
+      (push-mark)
+      (dolist (target targets-to-print)
+        (insert (cdr (assoc target results-alist)))))))
+
+(cl-defun slime-eval-save
+    (string &optional (targets-to-save '(common-lisp:*standard-output*
+                                         common-lisp:values)))
+  "Evaluate STRING in Lisp and save the result in the kill ring.
+
+Contents to be saved may be specified via optional parameter `targets-to-save' which should be a (multi)subset of list `slime-output-targets'."
+  (cl-assert (null (cl-set-difference targets-to-save slime-output-targets)))
+  (slime-eval-async `(swank:eval-and-grab-output ,string ',targets-to-save)
+    (lambda (results-alist)
+      (kill-new
+       (mapconcat (lambda (target) (cdr (assoc target results-alist)))
+                  targets-to-save ""))
+      (message "Evaluation finished; pushed result to kill ring."))))
 
 (defun slime-eval-describe (form)
   "Evaluate FORM in Lisp and display the result in a new buffer."

swank.lisp

@@ -1761,14 +1761,52 @@ Errors are trapped and invoke our debugger."
         (finish-output)
         (format-values-for-echo-area values)))))
 
-(defslimefun eval-and-grab-output (string)
+(defslimefun eval-and-grab-output
+    (string &optional (targets-to-capture '(*standard-output* values)
+                                          targets-provided-p))
+  "Evaluate contents of STRING, return alist of results including various output streams. Possible keys in the returned alist should be listed in the value of `slime-output-targets' variable in `slime.el'."
   (with-buffer-syntax ()
     (with-retry-restart (:msg "Retry SLIME evaluation request.")
-      (let* ((s (make-string-output-stream))
-             (*standard-output* s)
-             (values (multiple-value-list (eval (from-string string)))))
-        (list (get-output-stream-string s) 
-              (format nil "~{~S~^~%~}" values))))))
+      (macrolet ((maybe-value-string (form)
+                   `(if (member 'values targets-to-capture)
+                        ,form
+                        ""))
+                 (maybe-output-stream-string (stream-symbol)
+                   `(if (member ',stream-symbol targets-to-capture)
+                        (get-output-stream-string ,stream-symbol)
+                        ""))
+                 (maybe-make-string-output-stream (stream-symbol)
+                   `(if (member ',stream-symbol targets-to-capture)
+                        (make-string-output-stream)
+                        ,stream-symbol)))
+        (let* ((*trace-output*
+                 (maybe-make-string-output-stream *trace-output*))
+               (*error-output*
+                 (maybe-make-string-output-stream *error-output*))
+               (*standard-output*
+                 (maybe-make-string-output-stream *standard-output*))
+               (values (multiple-value-list (eval (from-string string)))))
+          (if targets-provided-p
+              ;; It is not clear what would be the most natural order here.
+              ;; We picked the reversed binding order.
+              (list
+               (cons 'values
+                     (maybe-value-string (format nil "~{~S~^~%~}" values)))
+               (cons '*standard-output*
+                     (maybe-output-stream-string *standard-output*))
+               (cons '*error-output*
+                     (maybe-output-stream-string *error-output*))
+               (cons '*trace-output*
+                     (maybe-output-stream-string *trace-output*)))
+              ;; targets are not provided by callers
+              ;; who presume older interface (slime 2.26 or earlier)
+              ;; to eval-and-grab-output
+              ;; This check (and targets-provided-p argument itself)
+              ;; - can be dropped when Emacs 27 becomes unsupported
+              ;; - can very likely be dropped when Org 9.4 becomes unsupported
+              (list (maybe-output-stream-string *standard-output*)
+                    (maybe-value-string
+                     (format nil "~{~S~^~%~}" values)))))))))
 
 (defun eval-region (string)
   "Evaluate STRING.