Emit a diagnostic if a display name string is empty

Sources/TestingMacros/CMakeLists.txt

@@ -90,6 +90,7 @@ target_sources(TestingMacros PRIVATE
   Support/Additions/FunctionDeclSyntaxAdditions.swift
   Support/Additions/IntegerLiteralExprSyntaxAdditions.swift
   Support/Additions/MacroExpansionContextAdditions.swift
+  Support/Additions/StringLiteralExprSyntaxAdditions.swift
   Support/Additions/TokenSyntaxAdditions.swift
   Support/Additions/TriviaPieceAdditions.swift
   Support/Additions/TypeSyntaxProtocolAdditions.swift

Sources/TestingMacros/Support/Additions/StringLiteralExprSyntaxAdditions.swift

@@ -0,0 +1,30 @@
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+//
+
+import SwiftSyntax
+
+extension StringLiteralExprSyntax {
+  /// Whether or not this string literal expression is completely empty.
+  ///
+  /// The value of this property is `false` even if the literal contains one or
+  /// more interpolation segments whose evaluated expressions are an empty
+  /// string. The value is only `true` if this string literal contains only one
+  /// empty string segment.
+  var isEmptyLiteral: Bool {
+    guard segments.count == 1,
+          case let .stringSegment(stringSegment) = segments.first,
+          case let .stringSegment(text) = stringSegment.content.tokenKind
+    else {
+      return false
+    }
+
+    return text.isEmpty
+  }
+}

Sources/TestingMacros/Support/AttributeDiscovery.swift

@@ -149,6 +149,14 @@ struct AttributeInfo {
       }
     }
 
+    // If there was a display name but it's completely empty, emit a warning
+    // diagnostic since this can cause confusion isn't generally recommended.
+    // Note that this is only possible for string literal display names; the
+    // compiler enforces that raw identifiers must be non-empty.
+    if let displayName, displayName.isEmptyLiteral {
+      context.diagnose(.emptyDisplayName(displayName))
+    }
+
     // Remove leading "Self." expressions from the arguments of the attribute.
     // See _SelfRemover for more information. Rewriting a syntax tree discards
     // location information from the copy, so only invoke the rewriter if the

Sources/TestingMacros/Support/DiagnosticMessage.swift

@@ -643,6 +643,22 @@ struct DiagnosticMessage: SwiftDiagnostics.DiagnosticMessage {
     )
   }
 
+  /// Create a diagnostic message stating that a string literal expression
+  /// passed as the display name to a `@Test` or `@Suite` attribute is empty
+  /// but should not be.
+  ///
+  /// - Parameters:
+  ///   - displayNameExpr: The display name string literal expression.
+  ///
+  /// - Returns: A diagnostic message.
+  static func emptyDisplayName(_ displayNameExpr: StringLiteralExprSyntax) -> Self {
+    Self(
+      syntax: Syntax(displayNameExpr),
+      message: "Display name string should not be empty",
+      severity: .warning
+    )
+  }
+
   /// Create a diagnostic message stating that a declaration has two display
   /// names.
   ///

Tests/TestingMacrosTests/TestDeclarationMacroTests.swift

@@ -304,6 +304,14 @@ struct TestDeclarationMacroTests {
       // .serialized on a non-parameterized test function
       "@Test(.serialized) func f() {}":
         "Trait '.serialized' has no effect when used with a non-parameterized test function",
+
+      // empty display name string literal
+      #"@Test("") func f() {}"#:
+        "Display name string should not be empty",
+      ##"@Test(#""#) func f() {}"##:
+        "Display name string should not be empty",
+      #"@Suite("") struct S {}"#:
+        "Display name string should not be empty",
     ]
   )
   func apiMisuseWarnings(input: String, expectedMessage: String) throws {