Merge pull request #77477 from DougGregor/result-builder-empty-case-crash

[Result builder transform] Don't abort when we encounter a case with no statements

Author: DougGregor

lib/Sema/BuilderTransform.cpp

@@ -630,19 +630,6 @@ class ResultBuilderTransform
   transformCase(CaseStmt *caseStmt) {
     auto *body = caseStmt->getBody();
 
-    // Explicitly disallow `case` statements with empty bodies
-    // since that helps to diagnose other issues with switch
-    // statements by excluding invalid cases.
-    if (auto *BS = dyn_cast<BraceStmt>(body)) {
-      if (BS->getNumElements() == 0) {
-        // HACK: still allow empty bodies if typechecking for code
-        // completion. Code completion ignores diagnostics
-        // and won't get any types if we fail.
-        if (!ctx.SourceMgr.hasIDEInspectionTargetBuffer())
-          return std::nullopt;
-      }
-    }
-
     NullablePtr<Expr> caseVarRef;
     std::optional<UnsupportedElt> unsupported;
     SmallVector<ASTNode, 4> newBody;

test/Constraints/result_builder_empty_case.swift

@@ -0,0 +1,41 @@
+// RUN: %target-swift-emit-silgen %s -verify | %FileCheck %s
+
+// Tests for a crash that occurred when the result builder transform encountered
+// an empty case statement.
+protocol V { }
+
+struct EV: V { }
+
+@resultBuilder
+struct VB {
+  static func buildBlock(_ components: any V...) -> any V { EV() }
+  static func buildEither(first: any V) -> any V { first }
+  static func buildEither(second: any V) -> any V { second }
+}
+
+extension String: V { }
+
+enum E {
+    case a(Int)
+    case b(String)
+}
+
+struct S {
+  var flag: E
+
+  // CHECK-LABEL: sil hidden [ossa] @$s25result_builder_empty_case1SV4testAA1V_pyF
+  // CHECK: switch_enum
+  @VB
+  func test() -> any V {
+    switch flag {
+    case .a:
+      // When NOT_DEFINED is... not defined... this ends up being an empty case.
+      // We permit this
+#if NOT_DEFINED
+      EV()
+#endif
+    case .b:
+      EV()
+    }
+  }
+}