Add support for sparse checkouts (#1369)

* Add support for sparse checkouts

* sparse-checkout: optionally turn off cone mode

While it _is_ true that cone mode is the default nowadays (mainly for
performance reasons: code mode is much faster than non-cone mode), there
_are_ legitimate use cases where non-cone mode is really useful.

Let's add a flag to optionally disable cone mode.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

* Verify minimum Git version for sparse checkout

The `git sparse-checkout` command is available only since Git version
v2.25.0. The `actions/checkout` Action actually supports older Git
versions than that; As of time of writing, the minimum version is
v2.18.0.

Instead of raising this minimum version even for users who do not
require a sparse checkout, only check for this minimum version
specifically when a sparse checkout was asked for.

Suggested-by: Tingluo Huang <tingluohuang@github.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

* Support sparse checkout/LFS better

Instead of fetching all the LFS objects present in the current revision
in a sparse checkout, whether they are needed inside the sparse cone or
not, let's instead only pull the ones that are actually needed.

To do that, let's avoid running that preemptive `git lfs fetch` call in
case of a sparse checkout.

An alternative that was considered during the development of this patch
(and ultimately rejected) was to use `git lfs pull --include <path>...`,
but it turned out to be too inflexible because it requires exact paths,
not the patterns that are available via the sparse checkout definition,
and that risks running into command-line length limitations.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

---------

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Co-authored-by: Daniel <daniel.fernandez@feverup.com>

1 files changed, 51 insertions, 0 deletions

diff --git a/__test__/verify-sparse-checkout-non-cone-mode.sh b/__test__/verify-sparse-checkout-non-cone-mode.sh
new file mode 100755
index 0000000..0d5d56f
--- /dev/null
+++ b/__test__/verify-sparse-checkout-non-cone-mode.sh
@@ -0,0 +1,51 @@
+#!/bin/sh
+
+# Verify .git folder
+if [ ! -d "./sparse-checkout-non-cone-mode/.git" ]; then
+  echo "Expected ./sparse-checkout-non-cone-mode/.git folder to exist"
+  exit 1
+fi
+
+# Verify sparse-checkout (non-cone-mode)
+cd sparse-checkout-non-cone-mode
+
+ENABLED=$(git config --local --get-all core.sparseCheckout)
+
+if [ "$?" != "0" ]; then
+    echo "Failed to verify that sparse-checkout is enabled"
+    exit 1
+fi
+
+# Check that sparse-checkout is enabled
+if [ "$ENABLED" != "true" ]; then
+  echo "Expected sparse-checkout to be enabled (is: $ENABLED)"
+  exit 1
+fi
+
+SPARSE_CHECKOUT_FILE=$(git rev-parse --git-path info/sparse-checkout)
+
+if [ "$?" != "0" ]; then
+    echo "Failed to validate sparse-checkout"
+    exit 1
+fi
+
+# Check that sparse-checkout list is not empty
+if [ ! -f "$SPARSE_CHECKOUT_FILE" ]; then
+  echo "Expected sparse-checkout file to exist"
+  exit 1
+fi
+
+# Check that all folders from sparse-checkout exists
+for pattern in $(cat "$SPARSE_CHECKOUT_FILE")
+do
+  if [ ! -d "${pattern#/}" ]; then
+    echo "Expected directory '${pattern#/}' to exist"
+    exit 1
+  fi
+done
+
+# Verify that the root directory is not checked out
+if [ -f README.md ]; then
+  echo "Expected top-level files not to exist"
+  exit 1
+fi
\ No newline at end of file