Make supportsAtomicCreateNewFile return true as default

The method org.eclipse.jgit.util.FS.supportsAtomicCreateNewFile()
should default to true as mentioned in docs [1]

org.eclipse.jgit.util.FS_POSIX.supportsAtomicCreateNewFile() method
will set the value to false if the git config
core.supportsatomiccreatenewfile is not set.

It should default to true if the configuration is undefined.

[1]
4169a95a65/org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java (L372)

Bug: 544164
Change-Id: I16ccf989a89da2cf4975c200b3228b25ba4c0d55
Signed-off-by: Vishal Devgire <vishaldevgire@gmail.com>
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/META-INF/MANIFEST.MF

@@ -68,6 +68,8 @@ Import-Package: com.googlecode.javaewah;version="[1.1.6,2.0.0)",
  org.junit.rules;version="[4.12,5.0.0)",
  org.junit.runner;version="[4.12,5.0.0)",
  org.junit.runners;version="[4.12,5.0.0)",
+ org.mockito;version="[2.23.0,3.0.0)",
+ org.mockito.stubbing;version="2.23.0",
  org.slf4j;version="[1.7.0,2.0.0)",
  org.tukaani.xz;version="[1.6.0,2.0)"
 Require-Bundle: org.hamcrest.core;bundle-version="[1.1.0,2.0.0)",

org.eclipse.jgit.test/tst/org/eclipse/jgit/util/FS_POSIXTest.java

@@ -0,0 +1,125 @@
+/*
+ * Copyright (C) 2019, Vishal Devgire <vishaldevgire@gmail.com>
+ * and other copyright owners as documented in the project's IP log.
+ *
+ * This program and the accompanying materials are made available
+ * under the terms of the Eclipse Distribution License v1.0 which
+ * accompanies this distribution, is reproduced below, and is
+ * available at http://www.eclipse.org/org/documents/edl-v10.php
+ *
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or
+ * without modification, are permitted provided that the following
+ * conditions are met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above
+ *   copyright notice, this list of conditions and the following
+ *   disclaimer in the documentation and/or other materials provided
+ *   with the distribution.
+ *
+ * - Neither the name of the Eclipse Foundation, Inc. nor the
+ *   names of its contributors may be used to endorse or promote
+ *   products derived from this software without specific prior
+ *   written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
+ * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+ * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
+ * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
+ * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.eclipse.jgit.util;
+
+import org.eclipse.jgit.lib.ConfigConstants;
+import org.eclipse.jgit.storage.file.FileBasedConfig;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mockito;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class FS_POSIXTest {
+	private SystemReader originalSystemReaderInstance;
+
+	private FileBasedConfig mockSystemConfig;
+
+	private FileBasedConfig mockUserConfig;
+
+	@Before
+	public void setUp() throws Exception {
+		SystemReader systemReader = Mockito.mock(SystemReader.class);
+
+		originalSystemReaderInstance = SystemReader.getInstance();
+		SystemReader.setInstance(systemReader);
+
+		mockSystemConfig = mock(FileBasedConfig.class);
+		mockUserConfig = mock(FileBasedConfig.class);
+		when(systemReader.openSystemConfig(any(), any()))
+				.thenReturn(mockSystemConfig);
+		when(systemReader.openUserConfig(any(), any()))
+				.thenReturn(mockUserConfig);
+
+		when(mockSystemConfig.getString(ConfigConstants.CONFIG_CORE_SECTION,
+				null, ConfigConstants.CONFIG_KEY_SUPPORTSATOMICFILECREATION))
+						.thenReturn(null);
+	}
+
+	@After
+	public void tearDown() {
+		SystemReader.setInstance(originalSystemReaderInstance);
+	}
+
+	@Test
+	public void supportsAtomicCreateNewFile_shouldReturnSupportedAsDefault() {
+		assertTrue(new FS_POSIX().supportsAtomicCreateNewFile());
+	}
+
+	@Test
+	public void supportsAtomicCreateNewFile_shouldReturnTrueIfFlagIsSetInUserConfig() {
+		setAtomicCreateCreationFlag(mockUserConfig, "true");
+		assertTrue(new FS_POSIX().supportsAtomicCreateNewFile());
+	}
+
+	@Test
+	public void supportsAtomicCreateNewFile_shouldReturnTrueIfFlagIsSetInSystemConfig() {
+		setAtomicCreateCreationFlag(mockSystemConfig, "true");
+		assertTrue(new FS_POSIX().supportsAtomicCreateNewFile());
+	}
+
+	@Test
+	public void supportsAtomicCreateNewFile_shouldReturnFalseIfFlagUnsetInUserConfig() {
+		setAtomicCreateCreationFlag(mockUserConfig, "false");
+		assertFalse(new FS_POSIX().supportsAtomicCreateNewFile());
+	}
+
+	@Test
+	public void supportsAtomicCreateNewFile_shouldReturnFalseIfFlagUnsetInSystemConfig() {
+		setAtomicCreateCreationFlag(mockSystemConfig, "false");
+		assertFalse(new FS_POSIX().supportsAtomicCreateNewFile());
+	}
+
+	private void setAtomicCreateCreationFlag(FileBasedConfig config,
+			String value) {
+		when(config.getString(ConfigConstants.CONFIG_CORE_SECTION, null,
+				ConfigConstants.CONFIG_KEY_SUPPORTSATOMICFILECREATION))
+						.thenReturn(value);
+	}
+}

org.eclipse.jgit/src/org/eclipse/jgit/util/FS_POSIX.java

@@ -122,6 +122,10 @@ public class FS_POSIX extends FS {
 			ret = getAtomicFileCreationSupportOption(
 					SystemReader.getInstance().openSystemConfig(null, this));
 		}
+
+		if (ret == AtomicFileCreation.UNDEFINED) {
+			ret = AtomicFileCreation.SUPPORTED;
+		}
 		supportsAtomicCreateNewFile = ret;
 	}
 
@@ -139,7 +143,8 @@ public class FS_POSIX extends FS {
 					? AtomicFileCreation.SUPPORTED
 					: AtomicFileCreation.NOT_SUPPORTED;
 		} catch (IOException | ConfigInvalidException e) {
-			return AtomicFileCreation.SUPPORTED;
+			LOG.error(e.getMessage(), e);
+			return AtomicFileCreation.UNDEFINED;
 		}
 	}