From b56e084c77914a7fde558e8fd28a218759a4ddd7 Mon Sep 17 00:00:00 2001
From: Mark H Weaver <mhw@netris.org>
Date: Thu, 15 Mar 2018 23:22:26 -0400
Subject: [PATCH] Fix eta-conversion edge cases in peval.

Fixes <https://bugs.gnu.org/29520>.
Reported by Stefan Israelsson Tampe <stefan.itampe@gmail.com>.

* module/language/tree-il/peval.scm (peval)[lift-applied-lambda]: Before
performing eta-conversion, check that the variable(s) passed to the
inner 'apply' are not referenced from the inner lambda, and that the
number of required arguments would not be reduced by the conversion.
---
 module/language/tree-il/peval.scm | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/module/language/tree-il/peval.scm b/module/language/tree-il/peval.scm
index 993fa0ad6..13b7d9bc4 100644
--- a/module/language/tree-il/peval.scm
+++ b/module/language/tree-il/peval.scm
@@ -1585,11 +1585,15 @@ top-level bindings from ENV and return the resulting expression."
          (and (not opt) rest (not kw)
               (match body
                 (($ <primcall> _ 'apply
-                    (($ <lambda> _ _ (and lcase ($ <lambda-case>)))
+                    (($ <lambda> _ _ (and lcase ($ <lambda-case> _ req1)))
                      ($ <lexical-ref> _ _ sym)
                      ...))
                  (and (equal? sym gensyms)
                       (not (lambda-case-alternate lcase))
+                      (<= (length req) (length req1))
+                      (every (lambda (s)
+                               (= (lexical-refcount s) 1))
+                             sym)
                       lcase))
                 (_ #f))))
        (let* ((vars (map lookup-var gensyms))