[push, lfs] Tell the pre-push hook whether the push is a dry run

This is a feature that does not exist in C git: an external pre-push
hook doesn't know whether the push is run as a dry run. But for
internal hooks written in Java it is entirely possible to give a hook
this information.

In JGit with its internal LFS implementation, this enables us to not
perform LFS uploads in a dry run. This is kind of important because
EGit frequently does a dry-run before doing the actual push to give the
user a way to review what would be pushed before it actually happens.

Doing an LFS upload of potentially huge files during a dry-run is
wasteful, makes the dry run not actually a dry run, and leads to
uploading the same file twice if followed by a real push.

Use the information in the LfsPrePushHook to only do the initial call
to the LFS server, but then skipping the actual upload if the push is
a dry run. That way, a failure to contact the LFS server leads to an
error in the dry run, as it should.

Bug: 546567
Change-Id: I155430f27c4979d91096ba72fd95c3775dd3f28b
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

2 files changed, 26 insertions, 2 deletions

diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PrePushHook.java b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PrePushHook.java
index 535c6b9483..43dbc37f4f 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PrePushHook.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/hooks/PrePushHook.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2015 Obeo. and others
+ * Copyright (C) 2015, 2022 Obeo and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -38,6 +38,8 @@ public class PrePushHook extends GitHook<String> {
 
 	private String refs;
 
+	private boolean dryRun;
+
 	/**
 	 * Constructor for PrePushHook
 	 * <p>
@@ -145,6 +147,27 @@ public class PrePushHook extends GitHook<String> {
 	}
 
 	/**
+	 * Sets whether the push is a dry run.
+	 *
+	 * @param dryRun
+	 *            {@code true} if the push is a dry run, {@code false} otherwise
+	 * @since 6.2
+	 */
+	public void setDryRun(boolean dryRun) {
+		this.dryRun = dryRun;
+	}
+
+	/**
+	 * Tells whether the push is a dry run.
+	 *
+	 * @return {@code true} if the push is a dry run, {@code false} otherwise
+	 * @since 6.2
+	 */
+	protected boolean isDryRun() {
+		return dryRun;
+	}
+
+	/**
 	 * Set Refs
 	 *
 	 * @param toRefs
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PushProcess.java b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PushProcess.java
index 942dad46e0..b59ae0c450 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/transport/PushProcess.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/transport/PushProcess.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008, Marek Zawirski <marek.zawirski@gmail.com> and others
+ * Copyright (C) 2008, 2022 Marek Zawirski <marek.zawirski@gmail.com> and others
  *
  * This program and the accompanying materials are made available under the
  * terms of the Eclipse Distribution License v. 1.0 which is available at
@@ -166,6 +166,7 @@ class PushProcess {
 					if (prePush != null) {
 						try {
 							prePush.setRefs(willBeAttempted);
+							prePush.setDryRun(transport.isDryRun());
 							prePush.call();
 						} catch (AbortedByHookException | IOException e) {
 							throw new TransportException(e.getMessage(), e);