refactor(version-control-systems): Extract Git's CommandLineTool

Follow the pattern of `MercurialCommand` [1] and introduce a `GitCommand`.
Besides providing a better overview, this favors composition over
inheritance to emphasize that ORT's `Git` class is not a
`CommandLineTool`, but uses a `CommandLineTool`. Also, this allows to run
the Git CLI statically without the need to create a `Git` instance.

[1]: 5531820

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

plugins/package-managers/gradle-inspector/src/funTest/kotlin/GradleFunTest.kt

@@ -30,7 +30,7 @@ import io.kotest.matchers.should
 import org.ossreviewtoolkit.analyzer.create
 import org.ossreviewtoolkit.analyzer.resolveSingleProject
 import org.ossreviewtoolkit.model.toYaml
-import org.ossreviewtoolkit.plugins.versioncontrolsystems.git.Git
+import org.ossreviewtoolkit.plugins.versioncontrolsystems.git.GitCommand
 import org.ossreviewtoolkit.utils.common.Os
 import org.ossreviewtoolkit.utils.common.ProcessCapture
 import org.ossreviewtoolkit.utils.test.ExpensiveTag
@@ -61,7 +61,7 @@ class GradleFunTest : StringSpec() {
 
     override suspend fun afterSpec(spec: Spec) {
         // Reset the Gradle wrapper files to the committed state.
-        Git().run(projectDir, "checkout", "gradle/", "gradlew*")
+        GitCommand.run(projectDir, "checkout", "gradle/", "gradlew*")
     }
 
     init {

plugins/package-managers/gradle/src/funTest/kotlin/GradleFunTest.kt

@@ -30,7 +30,7 @@ import io.kotest.matchers.should
 import org.ossreviewtoolkit.analyzer.create
 import org.ossreviewtoolkit.analyzer.resolveSingleProject
 import org.ossreviewtoolkit.model.toYaml
-import org.ossreviewtoolkit.plugins.versioncontrolsystems.git.Git
+import org.ossreviewtoolkit.plugins.versioncontrolsystems.git.GitCommand
 import org.ossreviewtoolkit.utils.common.Os
 import org.ossreviewtoolkit.utils.common.ProcessCapture
 import org.ossreviewtoolkit.utils.test.ExpensiveTag
@@ -61,7 +61,7 @@ class GradleFunTest : StringSpec() {
 
     override suspend fun afterSpec(spec: Spec) {
         // Reset the Gradle wrapper files to the committed state.
-        Git().run(projectDir, "checkout", "gradle/", "gradlew*")
+        GitCommand.run(projectDir, "checkout", "gradle/", "gradlew*")
     }
 
     init {

plugins/package-managers/sbt/src/funTest/kotlin/SbtFunTest.kt

@@ -24,7 +24,7 @@ import io.kotest.matchers.shouldBe
 
 import org.ossreviewtoolkit.analyzer.analyze
 import org.ossreviewtoolkit.model.toYaml
-import org.ossreviewtoolkit.plugins.versioncontrolsystems.git.Git
+import org.ossreviewtoolkit.plugins.versioncontrolsystems.git.GitCommand
 import org.ossreviewtoolkit.utils.test.getAssetFile
 import org.ossreviewtoolkit.utils.test.matchExpectedResult
 import org.ossreviewtoolkit.utils.test.patchActualResult
@@ -36,7 +36,7 @@ class SbtFunTest : StringSpec({
         val expectedResult = matchExpectedResult(expectedResultFile, definitionFile)
 
         // Clean any previously generated POM files / target directories.
-        Git().run(definitionFile.parentFile, "clean", "-fd")
+        GitCommand.run(definitionFile.parentFile, "clean", "-fd")
 
         val ortResult = analyze(definitionFile.parentFile, packageManagers = setOf(Sbt.Factory()))
 
@@ -49,7 +49,7 @@ class SbtFunTest : StringSpec({
         val expectedResult = matchExpectedResult(expectedResultFile, definitionFile)
 
         // Clean any previously generated POM files / target directories.
-        Git().run(definitionFile.parentFile, "clean", "-fd")
+        GitCommand.run(definitionFile.parentFile, "clean", "-fd")
 
         val ortResult = analyze(definitionFile.parentFile, packageManagers = setOf(Sbt.Factory()))
 

plugins/version-control-systems/git/src/funTest/kotlin/GitFunTest.kt

@@ -86,7 +86,7 @@ class GitFunTest : WordSpec({
             val revision = branches.getValue(branch)
 
             git.updateWorkingTree(workingTree, branch)
-            git.run("reset", "--hard", "HEAD~1", workingDir = repoDir)
+            GitCommand.run("reset", "--hard", "HEAD~1", workingDir = repoDir)
 
             git.updateWorkingTree(workingTree, branch) shouldBeSuccess branch
             workingTree.getRevision() shouldBe revision

plugins/version-control-systems/git/src/main/kotlin/Git.kt

@@ -67,7 +67,22 @@ private val REPOSITORY_URL_PREFIX_REPLACEMENTS = listOf(
     "git://" to "https://"
 )
 
-class Git : VersionControlSystem(), CommandLineTool {
+object GitCommand : CommandLineTool {
+    private val versionRegex = Regex("[Gg]it [Vv]ersion (?<version>[\\d.a-z-]+)(\\s.+)?")
+
+    override fun command(workingDir: File?) = "git"
+
+    // Require at least Git 2.29 on the client side as it has protocol "v2" enabled by default.
+    override fun getVersionRequirement(): RangesList = RangesListFactory.create(">=2.29")
+
+    override fun transformVersion(output: String): String =
+        versionRegex.matchEntire(output.lineSequence().first())?.let { match ->
+            @Suppress("UnsafeCallOnNullableType")
+            match.groups["version"]!!.value
+        }.orEmpty()
+}
+
+class Git : VersionControlSystem() {
     companion object {
         init {
             // Make sure that JGit uses the exact same authentication information as ORT itself. This addresses
@@ -99,30 +114,17 @@ class Git : VersionControlSystem(), CommandLineTool {
         }
     }
 
-    private val versionRegex = Regex("[Gg]it [Vv]ersion (?<version>[\\d.a-z-]+)(\\s.+)?")
-
     override val type = VcsType.GIT.toString()
     override val priority = 100
     override val latestRevisionNames = listOf("HEAD", "@")
 
-    override fun command(workingDir: File?) = "git"
-
-    override fun getVersion() = getVersion(null)
-
-    // Require at least Git 2.29 on the client side as it has protocol "v2" enabled by default.
-    override fun getVersionRequirement(): RangesList = RangesListFactory.create(">=2.29")
+    override fun getVersion() = GitCommand.getVersion(null)
 
     override fun getDefaultBranchName(url: String): String {
         val refs = Git.lsRemoteRepository().setRemote(url).callAsMap()
         return (refs["HEAD"] as? SymbolicRef)?.target?.name?.removePrefix("refs/heads/") ?: "master"
     }
 
-    override fun transformVersion(output: String): String =
-        versionRegex.matchEntire(output.lineSequence().first())?.let { match ->
-            @Suppress("UnsafeCallOnNullableType")
-            match.groups["version"]!!.value
-        }.orEmpty()
-
     override fun getWorkingTree(vcsDirectory: File): WorkingTree = GitWorkingTree(vcsDirectory, VcsType.forName(type))
 
     override fun isApplicableUrlInternal(vcsUrl: String): Boolean =
@@ -238,7 +240,7 @@ class Git : VersionControlSystem(), CommandLineTool {
         }.mapCatching { fetchResult ->
             // TODO: Migrate this to JGit once sparse checkout (https://bugs.eclipse.org/bugs/show_bug.cgi?id=383772) is
             //       implemented. Also see the "reset" call below.
-            run("checkout", revision, workingDir = workingTree.workingDir)
+            GitCommand.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.
@@ -262,7 +264,7 @@ class Git : VersionControlSystem(), CommandLineTool {
                     "Requested revision '$revision' not found in refs advertised by the server."
                 }
 
-                run("reset", "--hard", resolvedRevision, workingDir = workingTree.workingDir)
+                GitCommand.run("reset", "--hard", resolvedRevision, workingDir = workingTree.workingDir)
             }
 
             revision
@@ -288,7 +290,7 @@ class Git : VersionControlSystem(), CommandLineTool {
         }
     }
 
-    private fun WorkingTree.runGit(vararg args: String) = run(*args, workingDir = workingDir)
+    private fun WorkingTree.runGit(vararg args: String) = GitCommand.run(*args, workingDir = workingDir)
 }
 
 /**