(pp): Indent lines right when starting in col > 0

This refines the fix for bug#72561: commit 0a50019308 fixes
the bug by changing `ert--pp-with-indentation-and-newline`,
but it turns out that `pp` was inconsistent (it sometimes
indented the subsequent lines correctly and sometimes not,
depending on the current-buffer's major mode).
So the fix really should be in `pp`, which is what this patch does.

* lisp/emacs-lisp/pp.el (pp): Appropriately indent subsequent lines
if the first line is not inserted in column 0 (tho only when
printing into a buffer since otherwise it's somewhere between
ill-defined and impossible to implement).
* lisp/emacs-lisp/ert.el (ert--pp-with-indentation-and-newline):
Remove the indentation code after `pp` which was just working
around the bug in `pp`.  Also remove the redundant addition of
`\n` since `pp` always does it nowadays.
* test/lisp/help-mode-tests.el (help-mode-tests-xref-on-pp):
Fix thinko.

lisp/emacs-lisp/ert.el

@@ -1316,13 +1316,9 @@ empty string."
 (defun ert--pp-with-indentation-and-newline (object)
   "Pretty-print OBJECT, indenting it to the current column of point.
 Ensures a final newline is inserted."
-  (let ((begin (point))
-        (cols (current-column))
-        (pp-escape-newlines t)
+  (let ((pp-escape-newlines t)
         (print-escape-control-characters t))
-    (pp object (current-buffer))
-    (unless (bolp) (insert "\n"))
-    (indent-rigidly begin (point) cols)))
+    (pp object (current-buffer))))
 
 (defun ert--insert-infos (result)
   "Insert `ert-info' infos from RESULT into current buffer.

lisp/emacs-lisp/pp.el

@@ -308,17 +308,24 @@ can handle, whenever this is possible.
 Uses the pretty-printing code specified in `pp-default-function'.
 
 Output stream is STREAM, or value of `standard-output' (which see)."
-  (cond
-   ((and (eq (or stream standard-output) (current-buffer))
-         ;; Make sure the current buffer is setup sanely.
-         (eq (syntax-table) emacs-lisp-mode-syntax-table)
-         (eq indent-line-function #'lisp-indent-line))
-    ;; Skip the buffer->string->buffer middle man.
-    (funcall pp-default-function object)
-    ;; Preserve old behavior of (usually) finishing with a newline.
-    (unless (bolp) (insert "\n")))
-   (t
-    (princ (pp-to-string object) (or stream standard-output)))))
+  (let ((stream (or stream standard-output)))
+    (cond
+     ((and (eq stream (current-buffer))
+           ;; Make sure the current buffer is setup sanely.
+           (eq (syntax-table) emacs-lisp-mode-syntax-table)
+           (eq indent-line-function #'lisp-indent-line))
+      ;; Skip the buffer->string->buffer middle man.
+      (funcall pp-default-function object)
+      ;; Preserve old behavior of (usually) finishing with a newline.
+      (unless (bolp) (insert "\n")))
+     (t
+      (save-current-buffer
+        (when (bufferp stream) (set-buffer stream))
+        (let ((begin (point))
+              (cols (current-column)))
+          (princ (pp-to-string object) (or stream standard-output))
+          (when (and (> cols 0) (bufferp stream))
+            (indent-rigidly begin (point) cols))))))))
 
 ;;;###autoload
 (defun pp-display-expression (expression out-buffer-name &optional lisp)

test/lisp/help-mode-tests.el

@@ -92,7 +92,7 @@ Lisp concepts such as car, cdr, cons cell and list.")
 
 (ert-deftest help-mode-tests-xref-on-pp ()
   (with-temp-buffer
-    (insert (pp '(cons fill-column)))
+    (pp '(cons fill-column) (current-buffer))
     (help-xref-on-pp (point-min) (point-max))
     (goto-char (point-min))
     (search-forward "co")