Merge branch 'ab/fetch-nego'

Update to a few other topics around 'git fetch'.

* ab/fetch-nego:
  fetch doc: cross-link two new negotiation options
  negotiator: unknown fetch.negotiationAlgorithm should error out

Documentation/config.txt

@@ -1550,9 +1550,12 @@ fetch.negotiationAlgorithm::
 	sent when negotiating the contents of the packfile to be sent by the
 	server. Set to "skipping" to use an algorithm that skips commits in an
 	effort to converge faster, but may result in a larger-than-necessary
-	packfile; any other value instructs Git to use the default algorithm
+	packfile; The default is "default" which instructs Git to use the default algorithm
 	that never skips commits (unless the server has acknowledged it or one
 	of its descendants).
+	Unknown values will cause 'git fetch' to error out.
++
+See also the `--negotiation-tip` option for linkgit:git-fetch[1].
 
 format.attach::
 	Enable multipart/mixed attachments as the default for

Documentation/fetch-options.txt

@@ -57,6 +57,9 @@ commits reachable from any of the given commits.
 The argument to this option may be a glob on ref names, a ref, or the (possibly
 abbreviated) SHA-1 of a commit. Specifying a glob is equivalent to specifying
 this option multiple times, one for each matching ref name.
++
+See also the `fetch.negotiationAlgorithm` configuration variable
+documented in linkgit:git-config[1].
 
 ifndef::git-pull[]
 --dry-run::

fetch-negotiator.c

@@ -6,9 +6,15 @@
 void fetch_negotiator_init(struct fetch_negotiator *negotiator,
 			   const char *algorithm)
 {
-	if (algorithm && !strcmp(algorithm, "skipping")) {
-		skipping_negotiator_init(negotiator);
-		return;
+	if (algorithm) {
+		if (!strcmp(algorithm, "skipping")) {
+			skipping_negotiator_init(negotiator);
+			return;
+		} else if (!strcmp(algorithm, "default")) {
+			/* Fall through to default initialization */
+		} else {
+			die("unknown fetch negotiation algorithm '%s'", algorithm);
+		}
 	}
 	default_negotiator_init(negotiator);
 }

t/t5552-skipping-fetch-negotiator.sh

@@ -47,6 +47,29 @@ test_expect_success 'commits with no parents are sent regardless of skip distanc
 	have_not_sent c6 c4 c3
 '
 
+test_expect_success 'unknown fetch.negotiationAlgorithm values error out' '
+	rm -rf server client trace &&
+	git init server &&
+	test_commit -C server to_fetch &&
+
+	git init client &&
+	test_commit -C client on_client &&
+	git -C client checkout on_client &&
+
+	test_config -C client fetch.negotiationAlgorithm invalid &&
+	test_must_fail git -C client fetch "$(pwd)/server" 2>err &&
+	test_i18ngrep "unknown fetch negotiation algorithm" err &&
+
+	# Explicit "default" value
+	test_config -C client fetch.negotiationAlgorithm default &&
+	git -C client -c fetch.negotiationAlgorithm=default fetch "$(pwd)/server" &&
+
+	# Implementation detail: If there is nothing to fetch, we will not error out
+	test_config -C client fetch.negotiationAlgorithm invalid &&
+	git -C client fetch "$(pwd)/server" 2>err &&
+	test_i18ngrep ! "unknown fetch negotiation algorithm" err
+'
+
 test_expect_success 'when two skips collide, favor the larger one' '
 	rm -rf server client trace &&
 	git init server &&