Merge branch 'vd/scalar-to-main'

Hoist the remainder of "scalar" out of contrib/ to the main part of
the codebase.

* vd/scalar-to-main:
  Documentation/technical: include Scalar technical doc
  t/perf: add 'GIT_PERF_USE_SCALAR' run option
  t/perf: add Scalar performance tests
  scalar-clone: add test coverage
  scalar: add to 'git help -a' command list
  scalar: implement the `help` subcommand
  git help: special-case `scalar`
  scalar: include in standard Git build & installation
  scalar: fix command documentation section header

t/perf/README

@@ -95,6 +95,10 @@ You can set the following variables (also in your config.mak):
 	Git (e.g., performance of index-pack as the number of threads
 	changes). These can be enabled with GIT_PERF_EXTRA.
 
+    GIT_PERF_USE_SCALAR
+	Boolean indicating whether to register test repo(s) with Scalar
+	before executing tests.
+
 You can also pass the options taken by ordinary git tests; the most
 useful one is:
 

t/perf/p9210-scalar.sh

@@ -0,0 +1,39 @@
+#!/bin/sh
+
+test_description='test scalar performance'
+. ./perf-lib.sh
+
+test_perf_large_repo "$TRASH_DIRECTORY/to-clone"
+
+test_expect_success 'enable server-side partial clone' '
+	git -C to-clone config uploadpack.allowFilter true &&
+	git -C to-clone config uploadpack.allowAnySHA1InWant true
+'
+
+test_perf 'scalar clone' '
+	rm -rf scalar-clone &&
+	scalar clone "file://$(pwd)/to-clone" scalar-clone
+'
+
+test_perf 'git clone' '
+	rm -rf git-clone &&
+	git clone "file://$(pwd)/to-clone" git-clone
+'
+
+test_compare_perf () {
+	command=$1
+	shift
+	args=$*
+	test_perf "$command $args (scalar)" "
+		$command -C scalar-clone/src $args
+	"
+
+	test_perf "$command $args (non-scalar)" "
+		$command -C git-clone $args
+	"
+}
+
+test_compare_perf git status
+test_compare_perf test_commit --append --no-tag A
+
+test_done

t/perf/perf-lib.sh

@@ -49,6 +49,9 @@ export TEST_DIRECTORY TRASH_DIRECTORY GIT_BUILD_DIR GIT_TEST_CMP
 MODERN_GIT=$GIT_BUILD_DIR/bin-wrappers/git
 export MODERN_GIT
 
+MODERN_SCALAR=$GIT_BUILD_DIR/bin-wrappers/scalar
+export MODERN_SCALAR
+
 perf_results_dir=$TEST_RESULTS_DIR
 test -n "$GIT_PERF_SUBSECTION" && perf_results_dir="$perf_results_dir/$GIT_PERF_SUBSECTION"
 mkdir -p "$perf_results_dir"
@@ -120,6 +123,10 @@ test_perf_create_repo_from () {
 			# status" due to a locked index. Since we have
 			# a copy it's fine to remove the lock.
 			rm .git/index.lock
+		fi &&
+		if test_bool_env GIT_PERF_USE_SCALAR false
+		then
+			"$MODERN_SCALAR" register
 		fi
 	) || error "failed to copy repository '$source' to '$repo'"
 }
@@ -130,7 +137,11 @@ test_perf_fresh_repo () {
 	"$MODERN_GIT" init -q "$repo" &&
 	(
 		cd "$repo" &&
-		test_perf_do_repo_symlink_config_
+		test_perf_do_repo_symlink_config_ &&
+		if test_bool_env GIT_PERF_USE_SCALAR false
+		then
+			"$MODERN_SCALAR" register
+		fi
 	)
 }
 

t/perf/run

@@ -171,6 +171,9 @@ run_subsection () {
 	get_var_from_env_or_config "GIT_PERF_MAKE_COMMAND" "perf" "makeCommand"
 	get_var_from_env_or_config "GIT_PERF_MAKE_OPTS" "perf" "makeOpts"
 
+	get_var_from_env_or_config "GIT_PERF_USE_SCALAR" "perf" "useScalar" "--bool"
+	export GIT_PERF_USE_SCALAR
+
 	get_var_from_env_or_config "GIT_PERF_REPO_NAME" "perf" "repoName"
 	export GIT_PERF_REPO_NAME