improve error message for deduced executableTarget (#3254)

motivation: include the name of the target in the warning so its more actionable

changes: add the target name in the "use executableTarget in 5.4" warning

rdar://74045851

Author: tomerd

Sources/PackageLoading/PackageBuilder.swift

@@ -752,7 +752,7 @@ public final class PackageBuilder {
         default:
             targetType = sources.computeTargetType()
             if targetType == .executable && manifest.toolsVersion >= .v5_4 && warnAboutImplicitExecutableTargets {
-                diagnostics.emit(warning: "in tools version \(ToolsVersion.v5_4) and later, use 'executableTarget()' to declare executable targets")
+                diagnostics.emit(warning: "'\(potentialModule.name)' was identified as an executable target given the presence of a 'main.swift' file. Starting with tools version \(ToolsVersion.v5_4) executable targets should be declared as 'executableTarget()'")
             }
         }
 

Tests/PackageLoadingTests/PackageBuilderTests.swift

@@ -482,7 +482,7 @@ class PackageBuilderTests: XCTestCase {
             ]
         )
         PackageBuilderTester(manifest, in: fs) { package, diagnostics in
-            diagnostics.check(diagnostic: "in tools version 5.4.0 and later, use 'executableTarget()' to declare executable targets", behavior: .warning)
+            diagnostics.check(diagnostic: "'exec2' was identified as an executable target given the presence of a 'main.swift' file. Starting with tools version 5.4.0 executable targets should be declared as 'executableTarget()'", behavior: .warning)
             package.checkModule("lib") { _ in }
             package.checkModule("exec2") { _ in }
             package.checkProduct("exec2") { product in