Set error message for missing build targets in scheme

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 #### Fixed
 - Fixed regression on **.storekit** configuration files' default build phase. [#1026](https://github.com/yonaskolb/XcodeGen/pull/1026) @jcolicchio
+- Fixed bug where schemes without a build target would crash instead of displaying an error [#1040](https://github.com/yonaskolb/XcodeGen/pull/1040) @dalemyers
 
 #### Internal
 - Build universal binaries for release. XcodeGen now runs natively on Apple Silicon. [#1024](https://github.com/yonaskolb/XcodeGen/pull/1024) @thii

Sources/XcodeGenKit/SchemeGenerator.swift

@@ -165,7 +165,10 @@ public class SchemeGenerator {
         if let targetName = scheme.run?.executable {
             schemeTarget = project.getTarget(targetName)
         } else {
-            let name = scheme.build.targets.first { $0.buildTypes.contains(.running) }?.target.name ?? scheme.build.targets.first!.target.name
+            guard let firstTarget = scheme.build.targets.first else {
+                throw SchemeGenerationError.missingBuildTargets(scheme.name)
+            }
+            let name = scheme.build.targets.first { $0.buildTypes.contains(.running) }?.target.name ?? firstTarget.target.name
             schemeTarget = target ?? project.getTarget(name)
         }
 
@@ -350,13 +353,16 @@ enum SchemeGenerationError: Error, CustomStringConvertible {
 
     case missingTarget(TargetReference, projectPath: String)
     case missingProject(String)
+    case missingBuildTargets(String)
 
     var description: String {
         switch self {
         case .missingTarget(let target, let projectPath):
             return "Unable to find target named \"\(target)\" in \"\(projectPath)\""
         case .missingProject(let project):
             return "Unable to find project reference named \"\(project)\" in project.yml"
+        case .missingBuildTargets(let name):
+            return "Unable to find at least one build target in scheme \"\(name)\""
         }
     }
 }