From a0c126423c0de8be4e5f997b1a82e51aef953bbf Mon Sep 17 00:00:00 2001
From: Peter Bex <address@hidden>
Date: Fri, 5 Apr 2019 16:15:23 +0200
Subject: [PATCH] Reject import of module currently being defined (fixes #1506)

---
 NEWS       | 6 ++++++
 expand.scm | 6 +++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/NEWS b/NEWS
index 825acbfb..dba12ad9 100644
--- a/NEWS
+++ b/NEWS
@@ -6,6 +6,12 @@
   - When using (set-file-position!) on a port, its EOF status will now
     be reset.
 
+- Module system
+  - When you try to import the module you are currently defining into
+    itself, an error will be raised.  This prevents an infinite loop
+    in the compiler when later trying to import that same module.
+    (fixes #1506, thanks to Kristian Lein-Mathisen)
+
 5.0.1
 
 - Type system
diff --git a/expand.scm b/expand.scm
index ec302d48..7517b052 100644
--- a/expand.scm
+++ b/expand.scm
@@ -969,7 +969,11 @@
     (lambda (x r c)
       `(##core#begin
 	,@(map (lambda (x)
-		 (let-values (((name lib spec v s i) (##sys#decompose-import x r c 'import)))
+		 (let*-values (((name lib spec v s i) (##sys#decompose-import x r c 'import))
+			       ((mod) (##sys#current-module)))
+		   (when (and mod (eq? name (##sys#module-name mod)))
+		     (##sys#syntax-error-hook
+		      'import "cannot import from module currently being defined" name))
 		   (if (not spec)
 		       (##sys#syntax-error-hook
 			'import "cannot import from undefined module" name)
-- 
2.11.0