From 01987c093e2cfbd46115cc58e4ff9f789efb9d0d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Hugo=20H=C3=B6rnquist?= <hugo@lysator.liu.se>
Date: Thu, 7 Sep 2023 18:03:40 +0200
Subject: Enable let-env to unset variables.

---
 doc/ref/guile/util.texi | 3 +++
 module/hnh/util/env.scm | 6 +++++-
 tests/test/let-env.scm  | 5 +++++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/doc/ref/guile/util.texi b/doc/ref/guile/util.texi
index 72463407..7536a9bc 100644
--- a/doc/ref/guile/util.texi
+++ b/doc/ref/guile/util.texi
@@ -315,6 +315,9 @@ Converts @var{any} to a string, as per @var{display}.
 @defmac let-env bindings body ...
 Similar to @var{let}, but sets environment variables for the code in
 body. Restores the old values once we leave.
+
+A variable can also be removed from the environment, by setting its
+value to @code{#f}.
 @end defmac
 
 @defmac catch* thunk (symbol proc) ...
diff --git a/module/hnh/util/env.scm b/module/hnh/util/env.scm
index 18ec0543..bb42d966 100644
--- a/module/hnh/util/env.scm
+++ b/module/hnh/util/env.scm
@@ -14,7 +14,11 @@
                     (list n new-value (getenv n)))
                   (list (symbol->string (quote name)) ...)
                   (list value ...)))
-           (for-each (lambda (pair) (setenv (car pair) (cadr pair)))
+           (for-each (lambda (pair)
+                       (if (cadr pair)
+                           (setenv (car pair)
+                                   (cadr pair))
+                           (unsetenv (car pair))))
                      env-pairs))
          (lambda () body ...)
          (lambda ()
diff --git a/tests/test/let-env.scm b/tests/test/let-env.scm
index e3dc5927..a989776a 100644
--- a/tests/test/let-env.scm
+++ b/tests/test/let-env.scm
@@ -41,3 +41,8 @@
   (getenv "CALP_TEST_ENV"))
 
 
+(test-group "Unsetting environment"
+  (setenv "TEST" "A")
+  (let-env ((TEST #f))
+           (test-assert (not (getenv "TEST"))))
+  (test-equal "A" (getenv "TEST")))
-- 
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