[Emacs-diffs] scratch/raeburn-startup f01e8b5: Better fix for printing comma expressions.

[Ken Raeburn]

branch: scratch/raeburn-startup
commit f01e8b539bccd3a8404c4b7f8d058d1db82260a1
Author: Ken Raeburn <address@hidden>
Commit: Ken Raeburn <address@hidden>

    Better fix for printing comma expressions.
    
    The print-symbols-as-references processing for comma and related
    symbols works fine if they're being printed out as normal symbols.
    It's only in the special ",foo" style syntax where using "#N=" is
    likely to break things, because "#1=,foo" reads back as setting #1# to
    ,foo rather than to just the comma symbol.
    
    * src/print.c (print_object): When printing "," or related symbols
    with special syntax, don't use print_object on the special symbol
    itself.
    (PRINT_CIRCLE_CANDIDATE_P): Revert previous change.
---
 src/print.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/src/print.c b/src/print.c
index ff2e1be..38d9ac5 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1151,10 +1151,7 @@ print (Lisp_Object obj, Lisp_Object printcharfun, bool 
escapeflag)
        && ! NILP (Vprint_gensym))                                      \
    || (SYMBOLP (obj)                                                   \
        && SYMBOL_INTERNED_P (obj)                                      \
-       && ! NILP (Vprint_symbols_as_references)                                
\
-       && ! EQ (Qcomma, obj)                                           \
-       && ! EQ (Qcomma_at, obj)                                                
\
-       && ! EQ (Qcomma_dot, obj)))
+       && ! NILP (Vprint_symbols_as_references)))
 
 /* Construct Vprint_number_table according to the structure of OBJ.
    OBJ itself and all its elements will be added to Vprint_number_table
@@ -1607,7 +1604,20 @@ print_object (Lisp_Object obj, Lisp_Object printcharfun, 
bool escapeflag)
                   || EQ (XCAR (obj), Qcomma_at)
                   || EQ (XCAR (obj), Qcomma_dot)))
        {
-         print_object (XCAR (obj), printcharfun, false);
+         /* If print-symbols-as-references is enabled, symbols may
+            print with "#N=" or "#N#" form.  When we print a cons
+            cell with parens and separated elements, that's fine, but
+            for comma symbols we depend on the reader to generate the
+            cons cell from the special syntax.  The Lisp reader will
+            treat "#1=,#2=foo" as setting reference 1 to ",foo", not
+            to ",", so we can't use print_object to print out the
+            comma symbols without breaking the ability to read the
+            result back properly.  */
+         printchar (',', printcharfun);
+         if (EQ (XCAR (obj), Qcomma_at))
+           printchar ('@', printcharfun);
+         else if (EQ (XCAR (obj), Qcomma_dot))
+           printchar ('.', printcharfun);
          new_backquote_output--;
          print_object (XCAR (XCDR (obj)), printcharfun, escapeflag);
          new_backquote_output++;