bz-63874 Fix regression introduced by commit "Use commandline argument file for all options, but -J, for case javac"

This closes #105 pull request at github/apache/ant repo

WHATSNEW

@@ -10,6 +10,10 @@ Fixed bugs:
 
  * sshexec failed to write output to a file if the file didn't exist
 
+ * Fixes a regression in javac task involving command line argument
+   files.
+   Bugzilla Report 63874
+
 Other changes:
 --------------
 

src/main/org/apache/tools/ant/taskdefs/compilers/JavacExternal.java

@@ -66,7 +66,7 @@ public class JavacExternal extends DefaultCompilerAdapter {
         int firstFileName;
 
         if (assumeJava1_2Plus()) {
-            firstFileName = moveJOptionsToBeginning(commandLine);
+            firstFileName = moveArgFileEligibleOptionsToEnd(commandLine);
         } else {
             firstFileName = -1;
         }
@@ -77,31 +77,36 @@ public class JavacExternal extends DefaultCompilerAdapter {
     }
 
     /**
-     * Moves all -J arguments to the beginning
-     * So that all command line arguments could be written to file, but -J
+     * Moves all -J and @argfiles arguments to the beginning
+     * So that all command line arguments could be written to file, but -J and @argfile
      * As per javac documentation:
      *      you can specify one or more files that contain arguments to the javac command (except -J options)
      * @param commandLine command line to process
-     * @return int index of first non -J argument
+     * @return int index of first argument that could be put into argfile
      */
-    private int moveJOptionsToBeginning(String[] commandLine) {
-        int nonJArgumentIdx = 1; // 0 for javac executable
-        while(nonJArgumentIdx < commandLine.length && commandLine[nonJArgumentIdx].startsWith("-J")) {
-            nonJArgumentIdx++;
+    private int moveArgFileEligibleOptionsToEnd(String[] commandLine) {
+        int nonArgFileOptionIdx = 1; // 0 for javac executable
+        while(nonArgFileOptionIdx < commandLine.length &&
+                !isArgFileEligible(commandLine[nonArgFileOptionIdx])) {
+            nonArgFileOptionIdx++;
         }
 
-        for(int i = nonJArgumentIdx + 1; i < commandLine.length; i++) {
-            if (commandLine[i].startsWith("-J")) {
-                String jArgument = commandLine[i];
-                for(int j = i - 1; j >= nonJArgumentIdx; j--) {
+        for(int i = nonArgFileOptionIdx + 1; i < commandLine.length; i++) {
+            if (!isArgFileEligible(commandLine[i])) {
+                String option = commandLine[i];
+                for(int j = i - 1; j >= nonArgFileOptionIdx; j--) {
                     commandLine[j + 1] = commandLine[j];
                 }
-                commandLine[nonJArgumentIdx] = jArgument;
-                nonJArgumentIdx++;
+                commandLine[nonArgFileOptionIdx] = option;
+                nonArgFileOptionIdx++;
             }
         }
 
-        return nonJArgumentIdx;
+        return nonArgFileOptionIdx;
+    }
+
+    private static boolean isArgFileEligible(String option) {
+        return !(option.startsWith("-J") || option.startsWith("@"));
     }
 
     /**

src/tests/junit/org/apache/tools/ant/taskdefs/compilers/JavacExternalTest.java

@@ -28,6 +28,7 @@ import org.junit.Test;
 import java.io.File;
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.stream.Stream;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
@@ -131,6 +132,47 @@ public class JavacExternalTest {
         }
     }
 
+    @Test
+    public void argFileOptionIsMovedToBeginning() throws Exception {
+        final File workDir = createWorkDir("testSMC");
+        try {
+            final File src = new File(workDir, "src");
+            src.mkdir();
+            createFile(src, "org/apache/ant/tests/J1.java");
+            createFile(src, "org/apache/ant/tests/J2.java");
+            final File modules = new File(workDir, "modules");
+            modules.mkdir();
+            final Project prj = new Project();
+            prj.setBaseDir(workDir);
+            final Javac javac = new Javac();
+            javac.setProject(prj);
+            final Commandline[] cmd = new Commandline[1];
+            final TestJavacExternal impl = new TestJavacExternal();
+            final Path srcPath = new Path(prj);
+            srcPath.setLocation(src);
+            javac.setSrcdir(srcPath);
+            javac.createModulepath().setLocation(modules);
+            javac.setSource("9");
+            javac.setTarget("9");
+            javac.setFork(true);
+            javac.setMemoryInitialSize("80m");
+            javac.setExecutable("javacExecutable");
+            javac.add(impl);
+            javac.createCompilerArg().setValue("-g");
+            javac.createCompilerArg().setValue("@/home/my-compiler.args");
+            javac.execute();
+            assertEquals("javacExecutable", impl.getArgs()[0]);
+            assertEquals("-J-Xms80m", impl.getArgs()[1]);
+            assertEquals("@/home/my-compiler.args", impl.getArgs()[2]);
+            assertTrue(Stream.of(impl.getArgs()).anyMatch(x -> x.equals("-g")));
+            assertTrue(impl.getArgs()[impl.getArgs().length - 2].endsWith("J1.java"));
+            assertTrue(impl.getArgs()[impl.getArgs().length - 1].endsWith("J2.java"));
+            assertEquals(3, impl.getFirstFileName());
+        } finally {
+            delete(workDir);
+        }
+    }
+
     private File createWorkDir(String testName) {
         final File tmp = new File(System.getProperty("java.io.tmpdir"));   //NOI18N
         final File destDir = new File(tmp, String.format("%s%s%d",