Index: openacs-4/packages/acs-tcl/tcl/00-canisue-procs.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/acs-tcl/tcl/Attic/00-canisue-procs.tcl,v
diff -u -N
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ openacs-4/packages/acs-tcl/tcl/00-canisue-procs.tcl	5 Jun 2019 10:26:31 -0000	1.1.2.1
@@ -0,0 +1,72 @@
+ad_library {
+
+    An API for checking optional features (name inspired by caniuse.com)
+
+    @creation-date 4th June 2019
+    @author Gustaf Neumann
+}
+
+namespace eval ::acs {
+    ad_proc -public icanuse {feature} {
+
+        Check, if a (previously registered) feature can be used in an
+        installation. These features are typically version dependent
+        features of NaviServer. The checking of the availability of
+        these feratures is typically more complex than a plain "info
+        commands ...".
+
+        @param feature name for a feature, can contain blanks
+        @return boolean value
+
+    } {
+        return [info exists ::acs::caniuse($feature)]
+    }
+
+    ad_proc -public register_icanuse {feature condition} {
+
+        Registry function for acs::caniuse.
+
+        @param feature name for a feature, can contain blanks
+        @param condition expression to determine availability
+    } {
+        set success 0
+        try {
+            expr $condition
+        } on ok {result} {
+            set success $result
+        } on error {errorMsg} {
+            # just use the default
+            ns_log warning "registry for caniuse $feature -> $errorMsg"
+        }
+        if {$success} {
+            set ::acs::caniuse($feature) 1
+        }
+        ns_log notice "... I can use $feature -> $success"
+    }
+
+    ad_proc -private cmd_has_subcommand {cmd subcommand} {
+
+        Helper proc abusing error messages to determine, whether as
+        submethod is available.
+
+    } {
+        catch [list $cmd ""] errorMsg
+        return [expr {" $subcommand" in [split $errorMsg ","]}]
+    }
+}
+# Notice: can use 'ns_db currenthandles'
+
+::acs::register_icanuse "ns_db currenthandles" [acs::cmd_has_subcommand ns_db currenthandles]
+::acs::register_icanuse "ns_server ummap" [acs::cmd_has_subcommand ns_server unmap]
+#
+# "ns_server ummap" was introduced in NaviServer at the same time as
+# "ns_conn partialtimes" but the latter would requires a connection
+# (which is not available during loading).
+#
+::acs::register_icanuse "ns_conn partialtimes" [acs::icanuse "ns_server ummap"]
+
+# Local variables:
+#    mode: tcl
+#    tcl-indent-level: 4
+#    indent-tabs-mode: nil
+# End: