bug#70702: Useless error message from the reader: Error: invalid-read-syntax ("#")

[Alan Mackenzie <acm@muc.de>]

Hello, Emacs.

Recently, in my development version, I got the "error message":

    Error: invalid-read-syntax ("#")

while attempting to build Emacs.

This is an utterly useless error message:
(i) "#" is valid syntax in a .el or .elc file.  Only a subsequent
  character causes the invalidity.  The precise character sequence is not
  disclosed.
(ii) The source of the invalid character sequence, a file or buffer or
  string is kept secret.
(iii) The offset of the erring position in the file/buffer/string is not
  disclosed.  Neither is a line number or column number.
(iv) No context is given (e.g. the 32 characters before and after the
  "#").

This unhelpful message is a bug: a correct message would give at least
some of the information listed above.

The appearance, which surely must be false, is that the person
implementing the error messages was not attempting to help those affected
by them.

Come on, Emacs - we can do better than this.

-- 
Alan Mackenzie (Nuremberg, Germany).