allow overriding the project version with -Pversion=1.2.3, and add a fallback if there's no git repo

Author: aSemy

settings.gradle.kts

@@ -96,6 +96,17 @@ val currentCommitHash: Provider<String> =
     isIgnoreExitValue = true
   }.standardOutput.asText.map { it.trim() }
 
+/**
+ * The standard Gradle way of setting the version, which can be set on the CLI with
+ *
+ * ```shell
+ * ./gradlew -Pversion=1.2.3
+ * ```
+ *
+ * This can be used to override [gitVersion].
+ */
+val standardVersion: Provider<String> = providers.gradleProperty("version")
+
 /** Match simple SemVer tags. The first group is the `major.minor.patch` digits. */
 val semverRegex = Regex("""v((?:0|[1-9][0-9]*)\.(?:0|[1-9][0-9]*)\.(?:0|[1-9][0-9]*))""")
 
@@ -110,11 +121,13 @@ val gitVersion: Provider<String> =
       val head = descriptions.singleOrNull() ?: ""
       // drop the leading `v`, try to find the `major.minor.patch` digits group
       val headVersion = semverRegex.matchEntire(head)?.groupValues?.last()
-      headVersion ?: currentCommitHash.get() // fall back to using the git commit hash
+      headVersion
+        ?: currentCommitHash.orNull // fall back to using the git commit hash
+        ?: "unknown" // just in case there's no git repo, e.g. someone downloaded a zip archive
     }
   }
 
 gradle.allprojects {
-  extensions.add<Provider<String>>("gitVersion", gitVersion)
+  extensions.add<Provider<String>>("gitVersion", standardVersion.orElse(gitVersion))
 }
 //endregion