From 6aa29d1166137372ae0948d180a9f88e9edd4b94 Mon Sep 17 00:00:00 2001
From: Thomas Wolf <thomas.wolf@paranor.ch>
Date: Fri, 19 Nov 2021 19:15:46 +0100
Subject: [PATCH] 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>
(cherry picked from commit 9446e62733da5005be1d5182f0dce759a3052d4a)
---
 .../src/org/eclipse/jgit/util/FS.java         | 71 ++++++++++++++++---
 1 file 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 bf7b75369..507bd2bc9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/util/FS.java
@@ -61,6 +61,8 @@
 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;
@@ -96,6 +98,9 @@ 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;
 
 	/**
@@ -1508,26 +1513,76 @@ protected File discoverGitSystemConfig() {
 			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" }, //$NON-NLS-1$
+						Charset.defaultCharset().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" }, //$NON-NLS-1$
-				Charset.defaultCharset().name(), env);
+							"--show-origin", "--list", "-z" }, //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
+					Charset.defaultCharset().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);
+	}
 
-		return 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;
+	}
+
+	private long makeVersion(int major, int minor, int patch) {
+		return ((major * 10_000L) + minor) * 10_000L + patch;
 	}
 
 	/**