From: Mattias Engdegård <mattiase@acm.org>
Date: Thu, 27 May 2021 12:03:14 +0000 (+0200)
Subject: Don't propagate lexical variables into inlined functions
X-Git-Tag: emacs-28.0.90~2314
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=40d2970f4360bd942ffc3f86db9ff1499a5a5393;p=emacs.git

Don't propagate lexical variables into inlined functions

Functions compiled when inlined (thus from inside the optimiser)
mustn't retain the lexical environment of the caller or there will be
tears.  See discussion at
https://lists.gnu.org/archive/html/emacs-devel/2021-05/msg01227.html .

Bug found by Stefan Monnier.

* lisp/emacs-lisp/byte-opt.el (byte-compile-inline-expand):
Bind byte-optimize--lexvars to nil when re-entering the compiler
recursively.
* test/lisp/emacs-lisp/bytecomp-resources/bc-test-alpha.el:
* test/lisp/emacs-lisp/bytecomp-resources/bc-test-beta.el: New files.
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-defsubst): New test.
---

diff --git a/lisp/emacs-lisp/byte-opt.el b/lisp/emacs-lisp/byte-opt.el
index 99b5319ab3d..842697c7245 100644
--- a/lisp/emacs-lisp/byte-opt.el
+++ b/lisp/emacs-lisp/byte-opt.el
@@ -278,7 +278,10 @@
          ;; first, and then inline its byte-code.  This also has the advantage
          ;; that the final code does not depend on the order of compilation
          ;; of ELisp files, making the build more reproducible.
-         (byte-compile name)
+         ;; Since we are called from inside the optimiser, we need to make
+         ;; sure not to propagate lexvar values.
+         (dlet ((byte-optimize--lexvars nil))
+           (byte-compile name))
          `(,(symbol-function name) ,@(cdr form))))
 
       (_ ;; Give up on inlining.
diff --git a/test/lisp/emacs-lisp/bytecomp-resources/bc-test-alpha.el b/test/lisp/emacs-lisp/bytecomp-resources/bc-test-alpha.el
new file mode 100644
index 00000000000..6997d91b26a
--- /dev/null
+++ b/test/lisp/emacs-lisp/bytecomp-resources/bc-test-alpha.el
@@ -0,0 +1,9 @@
+;;; -*- lexical-binding: t -*-
+
+(require 'bc-test-beta)
+
+(defun bc-test-alpha-f (x)
+  (let ((y nil))
+    (list y (bc-test-beta-f x))))
+
+(provide 'bc-test-alpha)
diff --git a/test/lisp/emacs-lisp/bytecomp-resources/bc-test-beta.el b/test/lisp/emacs-lisp/bytecomp-resources/bc-test-beta.el
new file mode 100644
index 00000000000..9205a13d7d5
--- /dev/null
+++ b/test/lisp/emacs-lisp/bytecomp-resources/bc-test-beta.el
@@ -0,0 +1,6 @@
+;;; -*- lexical-binding: t -*-
+
+(defsubst bc-test-beta-f (y)
+  y)
+
+(provide 'bc-test-beta)
diff --git a/test/lisp/emacs-lisp/bytecomp-tests.el b/test/lisp/emacs-lisp/bytecomp-tests.el
index c9ab3ec1f1b..33413f5a002 100644
--- a/test/lisp/emacs-lisp/bytecomp-tests.el
+++ b/test/lisp/emacs-lisp/bytecomp-tests.el
@@ -1312,6 +1312,24 @@ compiled correctly."
                    (funcall f 3))
                  4)))
 
+(declare-function bc-test-alpha-f (ert-resource-file "bc-test-alpha.el"))
+
+(ert-deftest bytecomp-defsubst ()
+  ;; Check that lexical variables don't leak into inlined code.  See
+  ;; https://lists.gnu.org/archive/html/emacs-devel/2021-05/msg01227.html
+
+  ;; First, remove any trace of the functions and package defined:
+  (fmakunbound 'bc-test-alpha-f)
+  (fmakunbound 'bc-test-beta-f)
+  (setq features (delq 'bc-test-beta features))
+  ;; Byte-compile one file that uses a function from another file that isn't
+  ;; compiled.
+  (let ((file (ert-resource-file "bc-test-alpha.el"))
+        (load-path (cons (ert-resource-directory) load-path)))
+    (byte-compile-file file)
+    (load-file (concat file "c"))
+    (should (equal (bc-test-alpha-f 'a) '(nil a)))))
+
 ;; Local Variables:
 ;; no-byte-compile: t
 ;; End: