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bug#46387: 28.0.50; Compiled code making a variable dynamic stopped work
From: |
Stefan Monnier |
Subject: |
bug#46387: 28.0.50; Compiled code making a variable dynamic stopped working |
Date: |
Tue, 09 Feb 2021 10:31:24 -0500 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/28.0.50 (gnu/linux) |
> There's a lack of clarity regarding the exact semantics of local
> `defvar`. The manual says that its effect is confined to the current
> lexical scope, but what exactly does that mean?
Adding a variable to the context creates a new scope.
A `progn` should not introduce a new scope.
> As it turns out, parts of the implementation have different opinions
> about that.
Indeed, there's a fair bit a space between my above two statements.
> As you observed, the recently added optimisation on master takes
> a strict syntactic view: even a `progn` is a lexical scope,
I think that's clearly an error. Adding/removing `progn` shouldn't make
any difference in this respect.
> (Stefan, it looks like your latest Gnus patch may fall in the same trap. Or?)
The (with-suppressed-warnings (...) (defvar)) form is used at
several places. It's the preferred way to declare a variable
dynamically scoped without incurring the "not prefixed" warning and
without making the `with-suppressed-warnings` silencer cover more code
than intended.
Stefan