Read user.name and email from environment first

According to [1] user name and email are taken first from the
environment variables:
GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL
GIT_COMMITTER_NAME, GIT_COMMITTER_EMAIL

In case (some of) these environment variables are not set, the
information is taken from the git configuration.

JGit doesn not yet support the environment variables GIT_AUTHOR_DATE and
GIT_COMMITTER_DATE.

[1] https://www.kernel.org/pub/software/scm/git/docs/git-commit-tree.html#_commit_information

Bug: 460586
Change-Id: I3ba582b4ae13674cf319652b5b13ebcbb96dd8ec
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ConfigTest.java

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ConfigTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ConfigTest.java
index 69926f9..db31fd3 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ConfigTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/lib/ConfigTest.java
@@ -186,6 +186,9 @@ public void test007_readUserConfig() {
 		assertFalse(localConfig.get(UserConfig.KEY).isAuthorEmailImplicit());
 
 		// the values are defined in the global configuration
+		// first clear environment variables since they would override
+		// configuration files
+		mockSystemReader.clearProperties();
 		userGitConfig.setString("user", null, "name", "global username");
 		userGitConfig.setString("user", null, "email", "author@globalemail");
 		authorName = localConfig.get(UserConfig.KEY).getAuthorName();
@@ -211,6 +214,20 @@ public void test007_readUserConfig() {
 		assertEquals("author@localemail", authorEmail);
 		assertFalse(localConfig.get(UserConfig.KEY).isCommitterNameImplicit());
 		assertFalse(localConfig.get(UserConfig.KEY).isCommitterEmailImplicit());
+
+		// also git environment variables are defined
+		mockSystemReader.setProperty(Constants.GIT_AUTHOR_NAME_KEY,
+				"git author name");
+		mockSystemReader.setProperty(Constants.GIT_AUTHOR_EMAIL_KEY,
+				"author@email");
+		localConfig.setString("user", null, "name", "local username");
+		localConfig.setString("user", null, "email", "author@localemail");
+		authorName = localConfig.get(UserConfig.KEY).getAuthorName();
+		authorEmail = localConfig.get(UserConfig.KEY).getAuthorEmail();
+		assertEquals("git author name", authorName);
+		assertEquals("author@email", authorEmail);
+		assertFalse(localConfig.get(UserConfig.KEY).isAuthorNameImplicit());
+		assertFalse(localConfig.get(UserConfig.KEY).isAuthorEmailImplicit());
 	}
 
 	@Test

org.eclipse.jgit/src/org/eclipse/jgit/lib/UserConfig.java

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/UserConfig.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/UserConfig.java
index 60ac6f1..b8d236c 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/UserConfig.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/UserConfig.java
@@ -172,12 +172,13 @@ public boolean isCommitterEmailImplicit() {
 	}
 
 	private static String getNameInternal(Config rc, String envKey) {
-		// try to get the user name from the local and global configurations.
-		String username = rc.getString("user", null, "name"); //$NON-NLS-1$ //$NON-NLS-2$
+		// try to get the user name for the system property GIT_XXX_NAME
+		String username = system().getenv(envKey);
 
 		if (username == null) {
-			// try to get the user name for the system property GIT_XXX_NAME
-			username = system().getenv(envKey);
+			// try to get the user name from the local and global
+			// configurations.
+			username = rc.getString("user", null, "name"); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 
 		return stripInvalidCharacters(username);
@@ -196,12 +197,12 @@ private static String getDefaultUserName() {
 	}
 
 	private static String getEmailInternal(Config rc, String envKey) {
-		// try to get the email from the local and global configurations.
-		String email = rc.getString("user", null, "email"); //$NON-NLS-1$ //$NON-NLS-2$
+		// try to get the email for the system property GIT_XXX_EMAIL
+		String email = system().getenv(envKey);
 
 		if (email == null) {
-			// try to get the email for the system property GIT_XXX_EMAIL
-			email = system().getenv(envKey);
+			// try to get the email from the local and global configurations.
+			email = rc.getString("user", null, "email"); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 
 		return stripInvalidCharacters(email);