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>

src/git-source-provider.ts

@@ -153,23 +153,26 @@ export async function getSource(settings: IGitSourceSettings): Promise<void> {
 
     // Fetch
     core.startGroup('Fetching the repository')
+    const fetchOptions: {filter?: string; fetchDepth?: number} = {}
+    if (settings.sparseCheckout) fetchOptions.filter = 'blob:none'
     if (settings.fetchDepth <= 0) {
       // Fetch all branches and tags
       let refSpec = refHelper.getRefSpecForAllHistory(
         settings.ref,
         settings.commit
       )
-      await git.fetch(refSpec)
+      await git.fetch(refSpec, fetchOptions)
 
       // When all history is fetched, the ref we're interested in may have moved to a different
       // commit (push or force push). If so, fetch again with a targeted refspec.
       if (!(await refHelper.testRef(git, settings.ref, settings.commit))) {
         refSpec = refHelper.getRefSpec(settings.ref, settings.commit)
-        await git.fetch(refSpec)
+        await git.fetch(refSpec, fetchOptions)
       }
     } else {
+      fetchOptions.fetchDepth = settings.fetchDepth
       const refSpec = refHelper.getRefSpec(settings.ref, settings.commit)
-      await git.fetch(refSpec, settings.fetchDepth)
+      await git.fetch(refSpec, fetchOptions)
     }
     core.endGroup()
 
@@ -185,12 +188,24 @@ export async function getSource(settings: IGitSourceSettings): Promise<void> {
     // LFS fetch
     // Explicit lfs-fetch to avoid slow checkout (fetches one lfs object at a time).
     // Explicit lfs fetch will fetch lfs objects in parallel.
-    if (settings.lfs) {
+    // For sparse checkouts, let `checkout` fetch the needed objects lazily.
+    if (settings.lfs && !settings.sparseCheckout) {
       core.startGroup('Fetching LFS objects')
       await git.lfsFetch(checkoutInfo.startPoint || checkoutInfo.ref)
       core.endGroup()
     }
 
+    // Sparse checkout
+    if (settings.sparseCheckout) {
+      core.startGroup('Setting up sparse checkout')
+      if (settings.sparseCheckoutConeMode) {
+        await git.sparseCheckout(settings.sparseCheckout)
+      } else {
+        await git.sparseCheckoutNonConeMode(settings.sparseCheckout)
+      }
+      core.endGroup()
+    }
+
     // Checkout
     core.startGroup('Checking out the ref')
     await git.checkout(checkoutInfo.ref, checkoutInfo.startPoint)
@@ -261,7 +276,11 @@ export async function cleanup(repositoryPath: string): Promise<void> {
 
   let git: IGitCommandManager
   try {
-    git = await gitCommandManager.createCommandManager(repositoryPath, false)
+    git = await gitCommandManager.createCommandManager(
+      repositoryPath,
+      false,
+      false
+    )
   } catch {
     return
   }
@@ -297,7 +316,8 @@ async function getGitCommandManager(
   try {
     return await gitCommandManager.createCommandManager(
       settings.repositoryPath,
-      settings.lfs
+      settings.lfs,
+      settings.sparseCheckout != null
     )
   } catch (err) {
     // Git is required for LFS