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src/eval.c: Fix bug#62419

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Yup, almost 40 years after ELisp first combined them, buffer-local
and let bindings still don't work quite right :-(

The "automatically buffer-local if set" semantics should follow the
principle that it becomes buffer-local iff the var's current binding
refers to the top-level/global/non-let binding.

* src/eval.c (let_shadows_buffer_binding_p): Disregard non-global
let-bindings.

* test/src/eval-tests.el (eval-test--bug62419): New test.
This commit is contained in:
Stefan Monnier 2023-04-02 17:45:58 -04:00
parent 00144fa287
commit 5223762e02
2 changed files with 21 additions and 1 deletions
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3
src/eval.c
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@ -3400,7 +3400,7 @@ DEFUN ("fetch-bytecode", Ffetch_bytecode, Sfetch_bytecode,
return object;
}
/* Return true if SYMBOL currently has a let-binding
/* Return true if SYMBOL's default currently has a let-binding
which was made in the buffer that is now current. */
bool
@ -3415,6 +3415,7 @@ let_shadows_buffer_binding_p (struct Lisp_Symbol *symbol)
struct Lisp_Symbol *let_bound_symbol = XSYMBOL (specpdl_symbol (p));
eassert (let_bound_symbol->u.s.redirect != SYMBOL_VARALIAS);
if (symbol == let_bound_symbol
&& p->kind != SPECPDL_LET_LOCAL /* bug#62419 */
&& EQ (specpdl_where (p), buf))
return 1;
}

19
test/src/eval-tests.el
View file

@ -247,4 +247,23 @@ expressions works for identifiers starting with period."
(should (equal (string-trim (buffer-string))
expected-messages))))))))
(defvar-local eval-test--local-var 'global)
(ert-deftest eval-test--bug62419 ()
(with-temp-buffer
(setq eval-test--local-var 'first-local)
(let ((eval-test--local-var t))
(kill-local-variable 'eval-test--local-var)
(setq eval-test--local-var 'second-local)
(should (eq eval-test--local-var 'second-local)))
;; FIXME: It's not completely clear if exiting the above `let'
;; should restore the buffer-local binding to `first-local'
;; (i.e. reset the value of the second buffer-local binding to the
;; first's initial value) or should do nothing (on the principle that
;; the first buffer-local binding doesn't exists any more so there's
;; nothing to restore). I think both semantics make sense.
;;(should (eq eval-test--local-var 'first-local))
)
(should (eq eval-test--local-var 'global)))
;;; eval-tests.el ends here