fix open_port with many unset env vars

The erlang:open_port spawn and spawn_executable directives can include
    an {env, Env} directive to set up environment variables for the
    spawned process. Variables can be unset with {"NameOfVariable",false}.
    A bug in ert/emulator/sys/unix/sys.c could cause unset variables
    to not be unset. This would typically happen if there where more
    variables to be unset than there where already set variables in the
    destination evironment.

    Fix this problem for unix and add a new regression test for it to
    the port test suite. Windows does not seem to have the same problem.

2 files changed, 18 insertions, 3 deletions

diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index 151fa06e8e..737ffd9f94 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -1328,10 +1328,18 @@ static char **build_unix_environment(char *block)
 	}
     }
 
-    for (j = 0; j < i; j++) {
+    for (j = 0; j < i; ) {
         size_t last = strlen(cpp[j])-1;
 	if (cpp[j][last] == '=' && strchr(cpp[j], '=') == cpp[j]+last) {
 	    cpp[j] = cpp[--len];
+	    if (len < i) {
+		i--;
+	    } else {
+		j++;
+	    }
+	}
+	else {
+	    j++;
 	}
     }
 
diff --git a/erts/emulator/test/port_SUITE.erl b/erts/emulator/test/port_SUITE.erl
index 66aff307a3..77fa75b78f 100644
--- a/erts/emulator/test/port_SUITE.erl
+++ b/erts/emulator/test/port_SUITE.erl
@@ -878,13 +878,20 @@ env2(Config) ->
 			    "nisse" = os:getenv(Long)
 		    end),
 
-
+    
     ?line env_slave(Temp, [{"must_define_something","some_value"},
-			   {"certainly_not_existing",false},
+			    {"certainly_not_existing",false},
                            {"ends_with_equal", "value="},
 			   {Long,false},
 			   {"glurf","a glorfy string"}]),
 
+    %% A lot of non existing variables (mingled with existing)
+    NotExistingList = [{lists:flatten(io_lib:format("V~p_not_existing",[X])),false} 
+                        ||  X <- lists:seq(1,150)],
+    ExistingList = [{lists:flatten(io_lib:format("V~p_existing",[X])),"a_value"} 
+                        ||  X <- lists:seq(1,150)],
+    ?line env_slave(Temp, lists:sort(ExistingList ++ NotExistingList)),
+
     ?line test_server:timetrap_cancel(Dog),
     ok.