Merge pull request #16 from adamnfish/copilot/fix-empty-user-config-parsing

Handle empty user config files in YAML parser

Author: adamnfish

core/src/main/scala/com/gu/devenv/Config.scala

@@ -39,10 +39,14 @@ object Config {
     } yield projectConfig
 
   def parseUserConfig(contents: String): Try[UserConfig] =
-    for {
-      json       <- parser.parse(contents).toTry
-      userConfig <- json.as[UserConfig].toTry
-    } yield userConfig
+    if (yamlIsEmpty(contents)) {
+      scala.util.Success(UserConfig(None, None))
+    } else {
+      for {
+        json       <- parser.parse(contents).toTry
+        userConfig <- json.as[UserConfig].toTry
+      } yield userConfig
+    }
 
   def mergeConfigs(
       projectConfig: ProjectConfig,
@@ -177,6 +181,15 @@ object Config {
       envList.map(env => env.name -> Json.fromString(env.value)): _*
     )
 
+  /** Parsing an empty YAML file throws an exception, but an empty YAML file is valid and should
+    * result in an empty configuration. We check for empty contents here.
+    */
+  private def yamlIsEmpty(text: String): Boolean =
+    text.linesIterator
+      .map(_.trim)
+      .filter(_.nonEmpty)
+      .forall(_.startsWith("#"))
+
   private def applyPlugins(
       projectPlugins: Plugins,
       userPlugins: Option[Plugins]

core/src/main/scala/com/gu/devenv/models.scala

@@ -30,6 +30,9 @@ case class UserConfig(
     plugins: Option[Plugins],
     dotfiles: Option[Dotfiles]
 )
+object UserConfig {
+  val empty = UserConfig(None, None)
+}
 
 enum ForwardPort {
   case SamePort(port: Int)

core/src/test/scala/com/gu/devenv/ConfigTest.scala

@@ -92,6 +92,23 @@ class ConfigTest
         )
       )
     }
+
+    "parses an empty user config file" in {
+      val emptyConfig = ""
+      val Success(userConfig) =
+        Config.parseUserConfig(emptyConfig).success
+      userConfig shouldBe UserConfig.empty
+    }
+
+    "parses a user config file with only comments" in {
+      val commentsOnlyConfig = """# This is a comment
+                                 |# Another comment
+                                 |""".stripMargin
+      val Success(userConfig) =
+        Config.parseUserConfig(commentsOnlyConfig).success
+
+      userConfig shouldBe UserConfig.empty
+    }
   }
 
   "mergeConfigs" - {