If no sparse-checkout parameter is specified, disable it

This should allow users to reuse existing folders when running
`actions/checkout` where a previous run asked for a sparse checkout but
the current run does not ask for a sparse checkout.

This fixes actions#1475

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

__test__/git-auth-helper.test.ts

@@ -727,6 +727,7 @@ async function setup(testName: string): Promise<void> {
     branchDelete: jest.fn(),
     branchExists: jest.fn(),
     branchList: jest.fn(),
+    disableSparseCheckout: jest.fn(),
     sparseCheckout: jest.fn(),
     sparseCheckoutNonConeMode: jest.fn(),
     checkout: jest.fn(),

__test__/git-directory-helper.test.ts

@@ -462,6 +462,7 @@ async function setup(testName: string): Promise<void> {
     branchList: jest.fn(async () => {
       return []
     }),
+    disableSparseCheckout: jest.fn(),
     sparseCheckout: jest.fn(),
     sparseCheckoutNonConeMode: jest.fn(),
     checkout: jest.fn(),

src/git-command-manager.ts

@@ -17,6 +17,7 @@ export interface IGitCommandManager {
   branchDelete(remote: boolean, branch: string): Promise<void>
   branchExists(remote: boolean, pattern: string): Promise<boolean>
   branchList(remote: boolean): Promise<string[]>
+  disableSparseCheckout(): Promise<void>
   sparseCheckout(sparseCheckout: string[]): Promise<void>
   sparseCheckoutNonConeMode(sparseCheckout: string[]): Promise<void>
   checkout(ref: string, startPoint: string): Promise<void>
@@ -171,6 +172,10 @@ class GitCommandManager {
     return result
   }
 
+  async disableSparseCheckout(): Promise<void> {
+    await this.execGit(['sparse-checkout', 'disable'])
+  }
+
   async sparseCheckout(sparseCheckout: string[]): Promise<void> {
     await this.execGit(['sparse-checkout', 'set', ...sparseCheckout])
   }

src/git-source-provider.ts

@@ -208,7 +208,9 @@ export async function getSource(settings: IGitSourceSettings): Promise<void> {
     }
 
     // Sparse checkout
-    if (settings.sparseCheckout) {
+    if (!settings.sparseCheckout) {
+      await git.disableSparseCheckout()
+    } else {
       core.startGroup('Setting up sparse checkout')
       if (settings.sparseCheckoutConeMode) {
         await git.sparseCheckout(settings.sparseCheckout)