Disable clearing echo-area when 'inhibit-message' is non-nil

* src/xdisp.c (clear_message): Don't clear echo-area if
'inhibit-message' is non-nil.

* etc/NEWS:
* doc/lispref/display.texi (Displaying Messages): Document the
above change.  (Bug#77257)

doc/lispref/display.texi

@@ -404,8 +404,10 @@ elapsed since the time the first message was emitted.
 
 @defvar inhibit-message
 When this variable is non-@code{nil}, @code{message} and related functions
-will not display any messages in the Echo Area.  Echo-area messages
-are still logged in the @file{*Messages*} buffer, though.
+will not display any messages in the Echo Area, and will also not clear
+previous echo-area messages when @code{message} is called with a
+@code{nil} or an empty argument.  Echo-area messages are still logged in
+the @file{*Messages*} buffer, though.
 @end defvar
 
 @defmac with-temp-message message &rest body

etc/NEWS

@@ -2154,6 +2154,12 @@ provide instructions for finding the definition.
 New convenience function 'find-function-update-type-alist' offers a
 concise way to update a symbol's 'find-function-type-alist' property.
 
++++
+** 'inhibit-message' can now inhibit clearing of the echo-area.
+Binding 'inhibit-message' to a non-nil value will now suppress both
+the display of messages and the clearing of the echo-area, such as
+caused by calling 'message' with a nil argument.
+
 ** Special Events
 
 +++

src/xdisp.c

@@ -13405,7 +13405,7 @@ clear_message (bool current_p, bool last_displayed_p)
 {
   Lisp_Object preserve = Qnil;
 
-  if (current_p)
+  if (current_p && !inhibit_message)
     {
       if (FUNCTIONP (Vclear_message_function)
           /* FIXME: (bug#63253) Same as for `set-message-function` above.  */