Index: portlint.tcl
===================================================================
--- portlint.tcl	(revision 48714)
+++ portlint.tcl	(working copy)
@@ -287,6 +287,13 @@
             incr warnings
         }
 
+        foreach phase {fetch checksum extract} {
+            if {[regexp "(^|\\s)${phase}\\s+\\{\\s*\\}" $line]} {
+                ui_warn "Line $lineno should not override the ${phase} phase; clear \"distfiles\" if the port has no distfiles"
+                incr warnings
+            }
+        }
+
         ### TODO: more checks to Portfile syntax
 
         incr lineno