fix(downloader): Fix updating the Git working tree for a branch

The `Git.updateWorkingTree` function called only `git checkout
$revision` after fetching. In case of a local branch that was already
cloned before, this did not update the local branch.

Fix this by calling `git reset --hard FETCH_HEAD` after the checkout if
the revision is not a fixed revision.

Signed-off-by: Martin Nonnenmacher <[email protected]>

downloader/src/funTest/kotlin/vcs/GitFunTest.kt

@@ -0,0 +1,93 @@
+/*
+ * Copyright (C) 2023 The ORT Project Authors (see <https://github.com/oss-review-toolkit/ort/blob/main/NOTICE>)
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ * License-Filename: LICENSE
+ */
+
+package org.ossreviewtoolkit.downloader.vcs
+
+import io.kotest.core.spec.style.WordSpec
+import io.kotest.engine.spec.tempdir
+import io.kotest.matchers.result.shouldBeSuccess
+import io.kotest.matchers.shouldBe
+import org.ossreviewtoolkit.downloader.WorkingTree
+import org.ossreviewtoolkit.model.VcsInfo
+import org.ossreviewtoolkit.model.VcsType
+import java.io.File
+
+private val branches = mapOf(
+    "main" to "6f09f276c4426c387c6663f54bbd45aea8d81dac",
+    "branch1" to "0c58ea81d5c8112affab7a9cd6308deb4bc51589",
+    "branch2" to "7a05ad3ad30b4ddbfac22e0b768fb91383f16d8d",
+    "branch3" to "b798693a551e4d0e96d09409948327178a9abbce"
+)
+
+private val tags = mapOf(
+    "tag1" to "0c58ea81d5c8112affab7a9cd6308deb4bc51589",
+    "tag2" to "7a05ad3ad30b4ddbfac22e0b768fb91383f16d8d",
+    "tag3" to "b798693a551e4d0e96d09409948327178a9abbce"
+)
+
+class GitFunTest : WordSpec({
+    val git = Git()
+    val vcsInfo = VcsInfo(
+        type = VcsType.GIT,
+        url = "https://github.com/oss-review-toolkit/ort-test-data-git.git",
+        revision = "main"
+    )
+
+    lateinit var repoDir: File
+    lateinit var workingTree : WorkingTree
+
+    beforeEach {
+        repoDir = tempdir()
+        workingTree = git.initWorkingTree(repoDir, vcsInfo)
+    }
+
+    "updateWorkingTree" should {
+        "update the working tree to the correct revision" {
+            branches.values.forEach { revision ->
+                git.updateWorkingTree(workingTree, revision) shouldBeSuccess revision
+                workingTree.getRevision() shouldBe revision
+            }
+        }
+
+        "update the working tree to the correct tag" {
+            tags.forEach { (tag, revision) ->
+                git.updateWorkingTree(workingTree, tag) shouldBeSuccess tag
+                workingTree.getRevision() shouldBe revision
+            }
+        }
+
+        "update the working tree to the correct branch" {
+            branches.forEach { (branch, revision) ->
+                git.updateWorkingTree(workingTree, branch) shouldBeSuccess branch
+                workingTree.getRevision() shouldBe revision
+            }
+        }
+
+        "update an outdated local branch" {
+            val branch = "branch1"
+            val revision = branches.getValue(branch)
+
+            git.updateWorkingTree(workingTree, branch)
+            git.run("reset", "--hard", "HEAD~1", workingDir = repoDir)
+
+            git.updateWorkingTree(workingTree, branch) shouldBeSuccess branch
+            workingTree.getRevision() shouldBe revision
+        }
+    }
+})

downloader/src/main/kotlin/vcs/Git.kt

@@ -174,7 +174,7 @@ class Git : VersionControlSystem(), CommandLineTool {
             Git(this).use { git ->
                 logger.info { "Updating working tree from '${workingTree.getRemoteUrl()}'." }
 
-                updateWorkingTreeWithoutSubmodules(git, revision).mapCatching {
+                updateWorkingTreeWithoutSubmodules(workingTree, git, revision).mapCatching {
                     // In case this throws the exception gets encapsulated as a failure.
                     if (recursive) updateSubmodules(workingTree)
 
@@ -183,7 +183,7 @@ class Git : VersionControlSystem(), CommandLineTool {
             }
         }
 
-    private fun updateWorkingTreeWithoutSubmodules(git: Git, revision: String): Result<String> =
+    private fun updateWorkingTreeWithoutSubmodules(workingTree: WorkingTree, git: Git, revision: String): Result<String> =
         runCatching {
             logger.info { "Trying to fetch only revision '$revision' with depth limited to $GIT_HISTORY_DEPTH." }
 
@@ -222,7 +222,6 @@ class Git : VersionControlSystem(), CommandLineTool {
             logger.info { "Could not fetch everything using JGit: ${it.collectMessages()}" }
             logger.info { "Falling back to Git CLI." }
 
-            val workingTree = GitWorkingTree(git.repository.workTree, VcsType.GIT)
             if (workingTree.isShallow()) {
                 workingTree.runGit("fetch", "--unshallow", "--tags", "origin")
             } else {
@@ -234,7 +233,13 @@ class Git : VersionControlSystem(), CommandLineTool {
             logger.warn { "Failed to fetch everything: ${it.collectMessages()}" }
         }.mapCatching {
             // TODO: Migrate this to JGit once https://bugs.eclipse.org/bugs/show_bug.cgi?id=383772 is implemented.
-            run("checkout", revision, workingDir = git.repository.workTree)
+            run("checkout", revision, workingDir = workingTree.workingDir)
+
+            // In case of a non-fixed revision (branch or tag) reset the working tree to ensure that the previously
+            // fetched changes are applied.
+            if (!isFixedRevision(workingTree, revision).getOrThrow()) {
+                run("reset", "--hard", "FETCH_HEAD", workingDir = workingTree.workingDir)
+            }
 
             revision
         }