Fix mishandling of symbols that look like numbers

* src/bignum.c (make_neg_biguint): New function.
* src/lread.c (read1): Do not mishandle an unquoted symbol
with name equal to something like "1\0x", i.e., a string
of numeric form followed by a NUL byte.
Formerly these symbols were misread as numbers.
(string_to_number): Change last argument from an integer flag
to a pointer to the length.  This lets the caller figure out
how much of the prefix was used.  All callers changed.
Add a fast path if the integer (sans sign) fits in uintmax_t.
Update comments and simplify now that bignums are present.
* src/print.c (print_object): Fix quoting of symbols that look
like numbers, by relying on string_to_number for the tricky
cases rather than trying to redo its logic, incorrectly.  For
example, (read (prin1-to-string '\1e+NaN)) formerly returned
"1e+NaN", which was wrong: a backslash is needed in the output
to prevent it from being read as a NaN.  Escape NO_BREAK_SPACE
too, since lread.c treats it like SPACE.
* test/src/print-tests.el (print-read-roundtrip):
Add tests illustrating the abovementioned bugs.

1 files changed, 14 insertions, 2 deletions

diff --git a/test/src/print-tests.el b/test/src/print-tests.el
index 091f1aa1afb..78e769f50e9 100644
--- a/test/src/print-tests.el
+++ b/test/src/print-tests.el
@@ -95,8 +95,20 @@ otherwise, use a different charset."
                      "--------\n"))))
 
 (ert-deftest print-read-roundtrip ()
-  (let ((sym '\’bar))
-    (should (eq (read (prin1-to-string sym)) sym))))
+  (let ((syms (list '## '& '* '+ '- '/ '0E '0e '< '= '> 'E 'E0 'NaN '\"
+                    '\# '\#x0 '\' '\'\' '\( '\) '\+00 '\, '\-0 '\. '\.0
+                    '\0 '\0.0 '\0E0 '\0e0 '\1E+ '\1E+NaN '\1e+ '\1e+NaN
+                    '\; '\? '\[ '\\ '\] '\` '_ 'a 'e 'e0 'x
+                    '{ '| '} '~ : '\’ '\’bar
+                    (intern "\t") (intern "\n") (intern " ")
+                    (intern "\N{NO-BREAK SPACE}")
+                    (intern "\N{ZERO WIDTH SPACE}")
+                    (intern "\0"))))
+    (dolist (sym syms)
+      (should (eq (read (prin1-to-string sym)) sym))
+      (dolist (sym1 syms)
+        (let ((sym2 (intern (concat (symbol-name sym) (symbol-name sym1)))))
+          (should (eq (read (prin1-to-string sym2)) sym2)))))))
 
 (ert-deftest print-bignum ()
   (let* ((str "999999999999999999999999999999999")