Better git system config finding

We've used "GIT_EDITOR=edit git config --system --edit" to determine
the location of the git system config for a long time. But git 2.34.0
always expects this command to have a tty, but there isn't one when
called from Java. If there isn't one, the Java process may get a
SIGTTOU from the child process and hangs.

Arguably it's a bug in C git 2.34.0 to unconditionally assume there
was a tty. But JGit needs a fix *now*, otherwise any application using
JGit will lock up if git 2.34.0 is installed on the machine.

Therefore, use a different approach if the C git found is 2.8.0 or
newer: parse the output of

  git config --system --show-origin --list -z

"--show-origin" exists since git 2.8.0; it prefixes the values with
the file name of the config file they come from, which is the system
config file for this command. (This works even if the first item in
the system config is an include.)

Bug: 577358
Change-Id: I3ef170ed3f488f63c3501468303119319b03575d
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

1 files changed, 63 insertions, 8 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
index dd656e5f2b..d0007ec219 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
@@ -59,6 +59,8 @@ import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.annotations.Nullable;
@@ -94,6 +96,9 @@ public abstract class FS {
 	 */
 	protected static final Entry[] NO_ENTRIES = {};
 
+	private static final Pattern VERSION = Pattern
+			.compile("\\s(\\d+)\\.(\\d+)\\.(\\d+)"); //$NON-NLS-1$
+
 	private volatile Boolean supportSymlinks;
 
 	/**
@@ -1516,26 +1521,76 @@ public abstract class FS {
 			return null;
 		}
 
-		// Trick Git into printing the path to the config file by using "echo"
-		// as the editor.
-		Map<String, String> env = new HashMap<>();
-		env.put("GIT_EDITOR", "echo"); //$NON-NLS-1$ //$NON-NLS-2$
+		if (parseVersion(v) < makeVersion(2, 8, 0)) {
+			// --show-origin was introduced in git 2.8.0. For older git: trick
+			// it into printing the path to the config file by using "echo" as
+			// the editor.
+			Map<String, String> env = new HashMap<>();
+			env.put("GIT_EDITOR", "echo"); //$NON-NLS-1$ //$NON-NLS-2$
+
+			String w;
+			try {
+				w = readPipe(gitExe.getParentFile(),
+						new String[] { gitExe.getPath(), "config", "--system", //$NON-NLS-1$ //$NON-NLS-2$
+								"--edit" }, //$NON-NLS-1$
+						SystemReader.getInstance().getDefaultCharset().name(),
+						env);
+			} catch (CommandFailedException e) {
+				LOG.warn(e.getMessage());
+				return null;
+			}
+			if (StringUtils.isEmptyOrNull(w)) {
+				return null;
+			}
 
+			return new File(w);
+		}
 		String w;
 		try {
 			w = readPipe(gitExe.getParentFile(),
 					new String[] { gitExe.getPath(), "config", "--system", //$NON-NLS-1$ //$NON-NLS-2$
-							"--edit" }, //$NON-NLS-1$
-					SystemReader.getInstance().getDefaultCharset().name(), env);
+							"--show-origin", "--list", "-z" }, //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
+					SystemReader.getInstance().getDefaultCharset().name());
 		} catch (CommandFailedException e) {
 			LOG.warn(e.getMessage());
 			return null;
 		}
-		if (StringUtils.isEmptyOrNull(w)) {
+		if (w == null) {
 			return null;
 		}
+		// We get NUL-terminated items; the first one will be a file name,
+		// prefixed by "file:". (Using -z is crucial, otherwise git quotes file
+		// names with special characters.)
+		int nul = w.indexOf(0);
+		if (nul <= 0) {
+			return null;
+		}
+		w = w.substring(0, nul);
+		int colon = w.indexOf(':');
+		if (colon < 0) {
+			return null;
+		}
+		w = w.substring(colon + 1);
+		return w.isEmpty() ? null : new File(w);
+	}
+
+	private long parseVersion(String version) {
+		Matcher m = VERSION.matcher(version);
+		if (m.find()) {
+			try {
+				return makeVersion(
+						Integer.parseInt(m.group(1)),
+						Integer.parseInt(m.group(2)),
+						Integer.parseInt(m.group(3)));
+			} catch (NumberFormatException e) {
+				// Ignore
+			}
+		}
+		return -1;
+	}
 
-		return new File(w);
+	private long makeVersion(int major, int minor, int patch) {
+		return ((major * 10_000L) + minor) * 10_000L + patch;
 	}
 
 	/**