GitWorkingTree: First try to use the pull remote of the current branch

Git supports multiple remotes per working tree. Previously, simply the
first remote in the order reported by Git was used, but this is not
necessarily the remote that we want. We are interested in where the code
in the working tree comes from, so first try to use the remote that the
currently checked out branch pulls from, and only afterwards fall back
to "origin", if present, or the first other remote.

Signed-off-by: Sebastian Schuberth <sebastian.schuberth@bosch-si.com>

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

@@ -25,6 +25,8 @@ import com.here.ort.utils.ProcessCapture
 
 import java.io.File
 
+private const val GIT_STATUS_BRANCH_UPSTREAM_PREFIX = "# branch.upstream "
+
 open class GitWorkingTree(workingDir: File, private val gitBase: GitBase) : WorkingTree(workingDir, gitBase.type) {
     override fun isValid(): Boolean {
         if (!workingDir.isDirectory) {
@@ -49,7 +51,8 @@ open class GitWorkingTree(workingDir: File, private val gitBase: GitBase) : Work
         return paths.associateWith { GitWorkingTree(root.resolve(it), gitBase).getInfo() }
     }
 
-    override fun getRemoteUrl() = gitBase.run(workingDir, "remote", "get-url", getFirstRemote()).stdout.trimEnd()
+    override fun getRemoteUrl() =
+        gitBase.run(workingDir, "remote", "get-url", getRemoteForCheckout()).stdout.trimEnd()
 
     override fun getRevision() = gitBase.run(workingDir, "rev-parse", "HEAD").stdout.trimEnd()
 
@@ -58,7 +61,7 @@ open class GitWorkingTree(workingDir: File, private val gitBase: GitBase) : Work
 
     private fun listRemoteRefs(namespace: String): List<String> {
         val tags = gitBase.run(workingDir, "-c", "credential.helper=", "-c", "core.askpass=echo", "ls-remote",
-            "--refs", getFirstRemote(), "refs/$namespace/*").stdout.trimEnd()
+            "--refs", getRemoteForCheckout(), "refs/$namespace/*").stdout.trimEnd()
         return tags.lines().map {
             it.split('\t').last().removePrefix("refs/$namespace/")
         }
@@ -68,5 +71,18 @@ open class GitWorkingTree(workingDir: File, private val gitBase: GitBase) : Work
 
     override fun listRemoteTags() = listRemoteRefs("tags")
 
-    private fun getFirstRemote() = gitBase.run(workingDir, "remote", "show", "-n").stdout.lineSequence().first()
+    private fun getRemoteForCheckout(): String {
+        // Get the remote the current branch (if any) is configured to pull from.
+        val status = gitBase.run(workingDir, "status", "-sb", "--porcelain=v2").stdout
+        status.lineSequence().find { line ->
+            line.startsWith(GIT_STATUS_BRANCH_UPSTREAM_PREFIX)
+        }?.let { upstreamBranch ->
+            return upstreamBranch.substringAfter(GIT_STATUS_BRANCH_UPSTREAM_PREFIX).substringBefore('/')
+        }
+
+        // In case we are not on a branch, fall back to listing all remotes. Prefer "origin" if present but otherwise
+        // return the first remote.
+        val remotes = gitBase.run(workingDir, "remote", "show", "-n").stdout.lines()
+        return remotes.find { it == "origin" } ?: remotes.first()
+    }
 }