From a09619f2598a1658feac6794e85bc61a07c4855f Mon Sep 17 00:00:00 2001
From: =?utf8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Thu, 2 Nov 2023 11:10:24 +0100
Subject: [PATCH] * src/print.c (print_object): Don't print empty hash-table
 data

Since no data is the default, this preserves bidirectional compatibility.
---
 src/print.c             | 37 +++++++++++++++++++++++--------------
 test/src/print-tests.el |  7 -------
 2 files changed, 23 insertions(+), 21 deletions(-)

diff --git a/src/print.c b/src/print.c
index 0a5f2ee48d4..d011962d85b 100644
--- a/src/print.c
+++ b/src/print.c
@@ -2603,21 +2603,30 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag)
 	    if (h->purecopy)
 	      print_c_string (" purecopy t", printcharfun);
 
-	    print_c_string (" data (", printcharfun);
-
 	    ptrdiff_t size = h->count;
-	    /* Don't print more elements than the specified maximum.  */
-	    if (FIXNATP (Vprint_length) && XFIXNAT (Vprint_length) < size)
-	      size = XFIXNAT (Vprint_length);
-
-	    print_stack_push ((struct print_stack_entry){
-		.type = PE_hash,
-		.u.hash.obj = obj,
-		.u.hash.nobjs = size * 2,
-		.u.hash.idx = 0,
-		.u.hash.printed = 0,
-		.u.hash.truncated = (size < h->count),
-	      });
+	    if (size > 0)
+	      {
+		print_c_string (" data (", printcharfun);
+
+		/* Don't print more elements than the specified maximum.  */
+		if (FIXNATP (Vprint_length) && XFIXNAT (Vprint_length) < size)
+		  size = XFIXNAT (Vprint_length);
+
+		print_stack_push ((struct print_stack_entry){
+		    .type = PE_hash,
+		    .u.hash.obj = obj,
+		    .u.hash.nobjs = size * 2,
+		    .u.hash.idx = 0,
+		    .u.hash.printed = 0,
+		    .u.hash.truncated = (size < h->count),
+		  });
+	      }
+	    else
+	      {
+		/* Empty table: we can omit the data entirely.  */
+		printchar (')', printcharfun);
+		--print_depth;   /* Done with this.  */
+	      }
 	    goto next_obj;
 	  }
 
diff --git a/test/src/print-tests.el b/test/src/print-tests.el
index aedaa9a4e06..ff3a6fe7483 100644
--- a/test/src/print-tests.el
+++ b/test/src/print-tests.el
@@ -367,13 +367,6 @@ otherwise, use a different charset."
       (remhash 1 h)
       (format "%S" h))))
 
-  (should
-   (string-match
-    "data ()"
-    (let ((h (make-hash-table)))
-      (let ((print-length 0))
-        (format "%S" h)))))
-
   (should
    (string-match
     "data (99 99)"
-- 
2.39.2