Fix [9b47029467631832]: testing existence of env(some_thing) destroys traces. With test-case demonstrating the problem.

2 files changed, 16 insertions, 3 deletions

diff --git a/generic/tclEnv.c b/generic/tclEnv.c
index 2cb240d..66ddb57 100644
--- a/generic/tclEnv.c
+++ b/generic/tclEnv.c
@@ -551,7 +551,8 @@ TclGetEnv(
  *	array.
  *
  * Results:
- *	Always returns NULL to indicate success.
+ *	Returns NULL to indicate success, or an error-message if the array
+ *	element being handled doesn't exist.
  *
  * Side effects:
  *	Environment variable changes get propagated. If the whole "env" array
@@ -609,8 +610,7 @@ EnvTraceProc(
 	const char *value = TclGetEnv(name2, &valueString);
 
 	if (value == NULL) {
-	    Tcl_UnsetVar2(interp, name1, name2, 0);
-	    return NULL;
+	    return (char *) "no such variable";
 	}
 	Tcl_SetVar2(interp, name1, name2, value, 0);
 	Tcl_DStringFree(&valueString);
diff --git a/tests/env.test b/tests/env.test
index 83d99e0..f9df4d6 100644
--- a/tests/env.test
+++ b/tests/env.test
@@ -314,6 +314,19 @@ test env-7.2 {[219226]: links to env elements should not be removed by read} {
     }}
 } ok
 
+test env-7.3 {[9b4702]: testing existence of env(some_thing) should not destroy trace} {
+    apply {{} {
+      catch {unset ::env(test7_3)}
+      proc foo args {
+        set ::env(test7_3) ok
+      }
+      trace add variable ::env(not_yet_existent) write foo
+      info exists ::env(not_yet_existent)
+      set ::env(not_yet_existent) "Now I'm here";
+      info exists ::env(test7_3)
+    }}
+} 1
+
 # Restore the environment variables at the end of the test.
 
 foreach name [array names env] {