Print a warning and don't create an output file if there is no input

to <concat>.

PR: 14310
Submitted by:	Gus Heck <gus.heck at olin.edu>


git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@273539 13f79535-47bb-0310-9956-ffa450edef68

src/etc/testcases/taskdefs/concat.xml

@@ -35,7 +35,9 @@
     <concat destfile="TESTDEST" append="true">
       <filelist dir="${basedir}" files="thisfiledoesnotexist"/>
     </concat>
-    <delete file="TESTDEST"/>
+    <available file="TESTDEST" property="TESTDEST.was.created"/>
+    <fail message="TESTDEST created for nonexistant files"
+          if="TESTDEST.was.created"/>
   </target>
 
 </project>

src/main/org/apache/tools/ant/taskdefs/Concat.java

@@ -266,6 +266,9 @@ public class Concat extends Task {
                 // Concatenate the files.
                 if (srcFiles != null) {
                     catFiles(fileSetBase, srcFiles);
+                } else {
+                    log("Warning: Concat received empty fileset.", 
+                        Project.MSG_WARN);
                 }
             }
         } finally {
@@ -317,6 +320,12 @@ public class Concat extends Task {
         }
 
         final int len = inputFileNames.size();
+        if (len == 0) {
+            log("Warning: Could not find any of the files specified " +
+                "in concat task.", Project.MSG_WARN);
+            return;
+        }
+
         String[] input = new String[len];
         inputFileNames.copyInto(input);