Throw error when deepen-since excludes all commits

In C Git, when a client fetches with "git fetch --shallow-since=<date>
origin <ref>", and all commits reachable from <ref> are older than
<date>, the server dies with a message "no commits selected for shallow
requests". That is, (1) the --shallow-since filter applies to the commit
pointed to by the ref itself, and (2) there is a check that at least one
commit is not filtered out. (The pack-protocol.txt documentation does
not describe this, but the C implementation does this.)

The implementation in commit 1bb430dc21 ("UploadPack: support
deepen-since in protocol v2", 2018-09-27) does neither (1) nor (2), so
do both of these.

Change-Id: I9946327a71627626ecce34ca2d017d2add8867fc
Signed-off-by: Jonathan Tan <jonathantanmy@google.com>

org.eclipse.jgit.test/tst/org/eclipse/jgit/transport/UploadPackTest.java

@@ -1279,6 +1279,26 @@ public void testV2FetchShallowSince() throws Exception {
 		assertTrue(client.hasObject(merge.toObjectId()));
 	}
 
+	@Test
+	public void testV2FetchShallowSince_noCommitsSelected() throws Exception {
+		PersonIdent person = new PersonIdent(remote.getRepository());
+
+		RevCommit tooOld = remote.commit()
+			.committer(new PersonIdent(person, 1500000000, 0)).create();
+
+		remote.update("branch1", tooOld);
+
+		thrown.expect(PackProtocolException.class);
+		thrown.expectMessage("No commits selected for shallow request");
+		uploadPackV2(
+			"command=fetch\n",
+			PacketLineIn.DELIM,
+			"deepen-since 1510000\n",
+			"want " + tooOld.toObjectId().getName() + "\n",
+			"done\n",
+			PacketLineIn.END);
+	}
+
 	@Test
 	public void testV2FetchUnrecognizedArgument() throws Exception {
 		thrown.expect(PackProtocolException.class);

org.eclipse.jgit/resources/org/eclipse/jgit/internal/JGitText.properties

@@ -467,6 +467,7 @@ newIdMustNotBeNull=New ID must not be null
 newlineInQuotesNotAllowed=Newline in quotes not allowed
 noApplyInDelete=No apply in delete
 noClosingBracket=No closing {0} found for {1} at index {2}.
+noCommitsSelectedForShallow=No commits selected for shallow request
 noCredentialsProvider=Authentication is required but no CredentialsProvider has been registered
 noHEADExistsAndNoExplicitStartingRevisionWasSpecified=No HEAD exists and no explicit starting revision was specified
 noHMACsupport=No {0} support: {1}

org.eclipse.jgit/src/org/eclipse/jgit/internal/JGitText.java

@@ -528,6 +528,7 @@ public static JGitText get() {
 	/***/ public String newlineInQuotesNotAllowed;
 	/***/ public String noApplyInDelete;
 	/***/ public String noClosingBracket;
+	/***/ public String noCommitsSelectedForShallow;
 	/***/ public String noCredentialsProvider;
 	/***/ public String noHEADExistsAndNoExplicitStartingRevisionWasSpecified;
 	/***/ public String noHMACsupport;

org.eclipse.jgit/src/org/eclipse/jgit/revwalk/DepthGenerator.java

@@ -135,6 +135,10 @@ RevCommit next() throws MissingObjectException,
 			if ((c.flags & RevWalk.PARSED) == 0)
 				c.parseHeaders(walk);
 
+			if (c.getCommitTime() < deepenSince) {
+				continue;
+			}
+
 			int newDepth = c.depth + 1;
 
 			for (RevCommit p : c.parents) {

org.eclipse.jgit/src/org/eclipse/jgit/transport/UploadPack.java

@@ -1168,8 +1168,10 @@ private void computeShallowsAndUnshallows(FetchRequest req,
 			}
 
 			RevCommit o;
+			boolean atLeastOne = false;
 			while ((o = depthWalk.next()) != null) {
 				DepthWalk.Commit c = (DepthWalk.Commit) o;
+				atLeastOne = true;
 
 				boolean isBoundary = (c.getDepth() == walkDepth) || c.isBoundary();
 
@@ -1185,6 +1187,10 @@ private void computeShallowsAndUnshallows(FetchRequest req,
 					unshallowFunc.accept(c.copy());
 				}
 			}
+			if (!atLeastOne) {
+				throw new PackProtocolException(
+					JGitText.get().noCommitsSelectedForShallow);
+			}
 		}
 	}