From d68748648b03905612a28cdc59f9c07e75290611 Mon Sep 17 00:00:00 2001
From: Christopher Vogt <oss.nsp@cvogt.org>
Date: Fri, 7 Mar 2025 12:04:13 -0500
Subject: [PATCH] improve error messages when no main classes can be found

---
 .../internal/metals/WorkspaceLspService.scala    | 16 +++++++++++++---
 .../metals/debug/DiscoveryFailures.scala         |  4 ++--
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/metals/src/main/scala/scala/meta/internal/metals/WorkspaceLspService.scala b/metals/src/main/scala/scala/meta/internal/metals/WorkspaceLspService.scala
index c22d39d91e4..868d46c20dc 100644
--- a/metals/src/main/scala/scala/meta/internal/metals/WorkspaceLspService.scala
+++ b/metals/src/main/scala/scala/meta/internal/metals/WorkspaceLspService.scala
@@ -882,10 +882,20 @@ class WorkspaceLspService(
                   }
               }(_ => true)
               .flatMap { mains =>
-                mains.headOption.fold(
+                mains.fold(
                   Future.failed[DebugSessionParams](
-                    DiscoveryFailures
-                      .NoMainClassFoundException(unresolvedParams.mainClass)
+                    Option(unresolvedParams.buildTarget)
+                      .map(buildTarget =>
+                        DiscoveryFailures
+                          .ClassNotFoundInBuildTargetException(
+                            unresolvedParams.mainClass,
+                            buildTarget,
+                          )
+                      )
+                      .getOrElse(
+                        DiscoveryFailures
+                          .NoMainClassFoundException(unresolvedParams.mainClass)
+                      )
                   )
                 )(Future.successful(_))
               }
diff --git a/metals/src/main/scala/scala/meta/internal/metals/debug/DiscoveryFailures.scala b/metals/src/main/scala/scala/meta/internal/metals/debug/DiscoveryFailures.scala
index 4e2c9d7ca63..b9ffd4fbb84 100644
--- a/metals/src/main/scala/scala/meta/internal/metals/debug/DiscoveryFailures.scala
+++ b/metals/src/main/scala/scala/meta/internal/metals/debug/DiscoveryFailures.scala
@@ -21,13 +21,13 @@ object DiscoveryFailures {
       className: String,
       buildTarget: String,
   ) extends Exception(
-        s"Class '$className' not found in build target '${buildTarget}'"
+        s"Main class '$className' not found in build target '${buildTarget}' (not considering dependencies)"
       )
 
   case class NoMainClassFoundException(
       className: String
   ) extends Exception(
-        s"Class '$className' not found in any build target"
+        s"Main class '$className' not found in any build target (not considering dependencies)"
       )
 
   case class BuildTargetNotFoundForPathException(path: AbsolutePath)