From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Paul Eggert Newsgroups: gmane.emacs.devel Subject: Re: scratch/accurate-warning-pos: Solid progress: the branch now bootstraps. 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: emacs-devel-bounces+ged-emacs-devel=m.gmane.org@gnu.org Original-Sender: "Emacs-devel" Xref: news.gmane.org gmane.emacs.devel:231466 Archived-At: On 11/27/18 1:53 PM, Alan Mackenzie wrote: > Macros would mess things up. For example, after expanding a macro like=20 > the contrived > (defmacro dehash (form) > (copy-tree form)) > > , how would the recorded cons locations be linked up with the resulting > form? People typically don't write macros like that, so we needn't tune our=20 design for it. More commonly, people write macros containing errors,=20 such as: =C2=A0 (defmacro face-attribute-specified-or (value default &rest body) =C2=A0=C2=A0=C2=A0 (let ((temp (make-symbol "value"))) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 `(or =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (let ((,temp ,value)) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 (if (eq ,te= mp 'unspecified) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0 (progn ,@body) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= default)) =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ,temp))) This has a parenthesization typo and the macro doesn't mean what the=20 user probably intended. For these macros, as I understand it the=20 symbols-with-pos approach messes up because the symbol associated with=20 the error was built by make-symbol and doesn't have a source code=20 position. In contrast, the cons-with-pos approach should return a good=20 location in the macro itself for the undeclared symbol (i.e., just=20 before the last ",temp"). One can also come up with examples where the symbols-with-pos approach=20 is better than the cons-with-pos approach. That is, neither approach=20 dominates the other. So, which approach would be better in practice? I=20 don't think we know. > the "slow" Emacs would somehow need to be used by the byte compiler=20 > after Emacs has been built, to continue to get accurate warning locatio= ns. That's easy enough: the fast Emacs can fork and exec the slow one, which=20 can be installed next to movemail etc. (Again, not that I like this=20 approach.)