[PATCH] Fix handling of the "else" case in the r7rs cond-expand form

[Otto Jung <otto.jung@vauplace.com>]

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Hello!

I found a bug and want to propose my fix for it.

Basically, when using --r7rs compatibility mode,
the "else" case of cond-expand in (define-library ...)
would not work correctly - it would simply be treated as "false".

I added a test case that demonstrates this.
Then applied the attached patch and tested it by running:

$ ./check-guile r7rs.test
Testing /home/user1/my/devel/guile/meta/guile ... r7rs.test
with GUILE_LOAD_PATH=/home/user1/my/devel/guile/test-suite
Running r7rs.test

Totals for this test run:
passes:                 1093
failures:               0
unexpected passes:      0
expected failures:      14
unresolved test cases:  0
untested test cases:    0
unsupported test cases: 0
errors:                 0

Thanks.


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From c729a264d952c0acb101ef941c7c021475f81a89 Mon Sep 17 00:00:00 2001
From: Otto Jung <otto.jung@vauplace.com>
Date: Wed, 14 Jun 2023 18:36:55 -0700
Subject: [PATCH 1/2] Fix handling of the "else" case in the r7rs cond-expand
 form

Ensure proper handling of the "else" clause in the cond-expand form of
r7rs' define-library.

According to the r7rs specification, ``the last clause of cond-expand can
be an "else clause" with the form (else expression ...)''[1]. Additionally,
``the cond-expand declaration follows the same syntax and semantics as the
cond-expand expression type''[2].

The default cond-expand of Guile and the cond-expand of (scheme base)
work correctly, but they were not used during the expansion of r7rs
define-library macro. Instead, it has special handling for it.

This commit fixes the handling of the else case whereas
previously an "else" found in cond-expand was treated like a feature
name.

* module/ice-9/r7rs-libraries.scm (define-library): handle the "else"
case properly.

[1] page 15 of the report
[1] page 28 of the report
---
 module/ice-9/r7rs-libraries.scm | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/module/ice-9/r7rs-libraries.scm b/module/ice-9/r7rs-libraries.scm
index 63a300a26..428b22035 100644
--- a/module/ice-9/r7rs-libraries.scm
+++ b/module/ice-9/r7rs-libraries.scm
@@ -64,8 +64,9 @@
            ;; FIXME: R7RS (features) isn't quite the same as
            ;; %cond-expand-features; see scheme/base.scm.
            (memq (syntax->datum #'id) %cond-expand-features))))
-      (syntax-case clauses ()
+      (syntax-case clauses (else)
         (() #'())  ; R7RS says this is not specified :-/
+        (((else decl ...)) #'(decl ...))
         (((test decl ...) . clauses)
          (if (has-req? #'test)
              #'(decl ...)
-- 
2.40.1


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From fa052f4b7cb2d3b28f8c8061326eeedea87af756 Mon Sep 17 00:00:00 2001
From: Otto Jung <otto.jung@vauplace.com>
Date: Thu, 15 Jun 2023 19:00:08 -0700
Subject: [PATCH 2/2] Add simple tests for r7rs define-library

* test-suite/tests/r7rs.test: add define-library test cases
---
 test-suite/tests/r7rs.test                     | 17 +++++++++++++++++
 test-suite/tests/test-libs/cond-expand-lib.sld |  7 +++++++
 test-suite/tests/test-libs/lib1.sld            |  5 +++++
 3 files changed, 29 insertions(+)
 create mode 100644 test-suite/tests/test-libs/cond-expand-lib.sld
 create mode 100644 test-suite/tests/test-libs/lib1.sld

diff --git a/test-suite/tests/r7rs.test b/test-suite/tests/r7rs.test
index 1cc8cd31e..5e404b6a7 100644
--- a/test-suite/tests/r7rs.test
+++ b/test-suite/tests/r7rs.test
@@ -45,6 +45,7 @@
 (define-module (test-suite r7rs)
   #:pure
   #:use-module ((guile) #:select (install-r7rs!
+                                  (eval . guile:eval) current-module
                                   define-syntax-rule quote read-disable
                                   import))
   #:use-module (test-suite lib))
@@ -741,6 +742,22 @@
           (set-kar! k 3)
           (kar k)))
 
+;; define-library
+
+(test 42
+      (guile:eval
+       `(begin
+          (import (tests test-libs lib1))
+          lib1-var)
+       (current-module)))
+
+(test 42
+      (guile:eval
+       `(begin
+          (import (tests test-libs cond-expand-lib))
+          cond-expand-var)
+       (current-module)))
+
 (test-end)
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
diff --git a/test-suite/tests/test-libs/cond-expand-lib.sld b/test-suite/tests/test-libs/cond-expand-lib.sld
new file mode 100644
index 000000000..2d8351384
--- /dev/null
+++ b/test-suite/tests/test-libs/cond-expand-lib.sld
@@ -0,0 +1,7 @@
+
+(define-library (tests test-libs cond-expand-lib)
+  (import (only (scheme base) begin define cond-expand))
+  (export cond-expand-var)
+  (cond-expand
+   (unsuported-feature (begin (define cond-expand-var 1)))
+   (else (begin (define cond-expand-var 42)))))
diff --git a/test-suite/tests/test-libs/lib1.sld b/test-suite/tests/test-libs/lib1.sld
new file mode 100644
index 000000000..ae83f5a68
--- /dev/null
+++ b/test-suite/tests/test-libs/lib1.sld
@@ -0,0 +1,5 @@
+
+(define-library (tests test-libs lib1)
+  (import (scheme base))
+  (export lib1-var)
+  (begin (define lib1-var 42)))
-- 
2.40.1