8198317: Enhance JavacTool.getTask for flexibility

Co-authored-by: Guoxiong Li <lgxbslgx@gmail.com>
Reviewed-by: jfranck

src/jdk.compiler/share/classes/com/sun/tools/javac/api/JavacTool.java

@@ -166,9 +166,15 @@ public final class JavacTool implements JavaCompiler {
             if (diagnosticListener != null)
                 context.put(DiagnosticListener.class, ccw.wrap(diagnosticListener));
 
-            if (out == null)
+            // If out is null and the value is set in the context, we need to do nothing.
+            if (out == null && context.get(Log.errKey) == null)
+                // Situation: out is null and the value is not set in the context.
                 context.put(Log.errKey, new PrintWriter(System.err, true));
-            else
+            else if (out instanceof PrintWriter pw)
+                // Situation: out is not null and out is a PrintWriter.
+                context.put(Log.errKey, pw);
+            else if (out != null)
+                // Situation: out is not null and out is not a PrintWriter.
                 context.put(Log.errKey, new PrintWriter(out, true));
 
             if (fileManager == null) {

test/langtools/tools/javac/api/TestContextLoggingOutput.java

@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8198317
+ * @summary Enhance JavacTool.getTask for flexibility
+ * @library /tools/lib
+ * @modules jdk.compiler/com.sun.tools.javac.api
+ *          jdk.compiler/com.sun.tools.javac.main
+ *          jdk.compiler/com.sun.tools.javac.util
+ * @build toolbox.ToolBox
+ * @run main TestContextLoggingOutput
+ */
+
+import java.io.StringWriter;
+import java.io.PrintWriter;
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.net.URI;
+import java.util.List;
+import java.util.Arrays;
+import javax.tools.ToolProvider;
+import javax.tools.SimpleJavaFileObject;
+import javax.tools.JavaFileObject;
+
+import toolbox.ToolBox;
+import toolbox.TestRunner;
+import static toolbox.ToolBox.lineSeparator;
+
+public class TestContextLoggingOutput extends TestRunner {
+    ToolBox tb;
+
+    public TestContextLoggingOutput() {
+        super(System.err);
+        tb = new ToolBox();
+    }
+
+    public static void main(String[] args) throws Exception {
+        TestContextLoggingOutput t = new TestContextLoggingOutput();
+        t.runTests();
+    }
+
+    @Test
+    public void testLogSettingInJavacTool() throws Exception {
+        String code = """
+                import java.io.Serializable;
+                class Test implements Serializable {
+                    public static final int serialVersionUID = 1;
+                }""";
+
+        List<String> expected = Arrays.asList(
+                "Test.java:3:29: compiler.warn.long.SVUID: Test",
+                "1 warning");
+
+        List<? extends JavaFileObject> files = Arrays.asList(new MemFile("Test.java", code));
+
+        // Situation: out is null and the value is not set in the context.
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        PrintStream printStream = new PrintStream(baos);
+        PrintStream prev = System.err;
+        try {
+            System.setErr(printStream);
+            ToolProvider.getSystemJavaCompiler()
+                    .getTask(null, null, null, Arrays.asList("-XDrawDiagnostics", "-Xlint:serial"), null, files)
+                    .call();
+            tb.checkEqual(expected, Arrays.asList(baos.toString().split(lineSeparator)));
+        } finally {
+            System.setErr(prev);
+        }
+
+        // Situation: out is not null and out is a PrintWriter.
+        StringWriter stringWriter2 = new StringWriter();
+        PrintWriter expectedPW2 = new PrintWriter(stringWriter2);
+        ToolProvider.getSystemJavaCompiler()
+                .getTask(expectedPW2, null, null, Arrays.asList("-XDrawDiagnostics", "-Xlint:serial"), null, files)
+                .call();
+        tb.checkEqual(expected, Arrays.asList(stringWriter2.toString().split(lineSeparator)));
+
+        // Situation: out is not null and out is not a PrintWriter.
+        StringWriter stringWriter3 = new StringWriter();
+        ToolProvider.getSystemJavaCompiler()
+                .getTask(stringWriter3, null, null, Arrays.asList("-XDrawDiagnostics", "-Xlint:serial"), null, files)
+                .call();
+        tb.checkEqual(expected, Arrays.asList(stringWriter3.toString().split(lineSeparator)));
+    }
+
+    class MemFile extends SimpleJavaFileObject {
+        public final String text;
+
+        MemFile(String name, String text) {
+            super(URI.create(name), JavaFileObject.Kind.SOURCE);
+            this.text = text;
+        }
+
+        @Override
+        public String getName() {
+            return uri.toString();
+        }
+
+        @Override
+        public String getCharContent(boolean ignoreEncodingErrors) {
+            return text;
+        }
+    }
+}