[Diagnostics] Result Builders: Improve diagnostic for unsupported observed vars

Author: xedin

include/swift/AST/DiagnosticsSema.def

@@ -5886,7 +5886,7 @@ ERROR(result_builder_requires_explicit_var_initialization,none,
       "local variable%select{| '%1'}0 requires explicit initializer to be used with "
       "result builder %2", (bool, StringRef, DeclName))
 ERROR(cannot_declare_computed_var_in_result_builder,none,
-      "cannot declare local %select{lazy|wrapped|computed}0 variable "
+      "cannot declare local %select{lazy|wrapped|computed|observed}0 variable "
       "in result builder", (unsigned))
 
 //------------------------------------------------------------------------------

lib/Sema/CSDiagnostics.cpp

@@ -5877,7 +5877,8 @@ bool SkipUnhandledConstructInResultBuilderFailure::diagnosePatternBinding(
   for (unsigned i : range(PB->getNumPatternEntries())) {
     auto *pattern = PB->getPattern(i);
 
-    // Each variable bound by the pattern must be stored.
+    // Each variable bound by the pattern must be stored and cannot have
+    // observers.
     {
       SmallVector<VarDecl *, 8> variables;
       pattern->collectVariables(variables);
@@ -5917,7 +5918,7 @@ bool SkipUnhandledConstructInResultBuilderFailure::diagnosePatternBinding(
 
 bool SkipUnhandledConstructInResultBuilderFailure::diagnoseStorage(
     VarDecl *var) const {
-  enum class PropertyKind : unsigned { lazy, wrapped, computed };
+  enum class PropertyKind : unsigned { lazy, wrapped, computed, observed };
 
   if (var->getImplInfo().isSimpleStored())
     return false;
@@ -5927,6 +5928,8 @@ bool SkipUnhandledConstructInResultBuilderFailure::diagnoseStorage(
     kind = PropertyKind::lazy;
   } else if (var->hasAttachedPropertyWrapper()) {
     kind = PropertyKind::wrapped;
+  } else if (var->hasObservers()) {
+    kind = PropertyKind::observed;
   } else {
     kind = PropertyKind::computed;
   }

test/Constraints/result_builder_invalid_vars.swift

@@ -20,15 +20,15 @@ dummy {
 }
 
 dummy {
-  var observedVar: Int = 123 { // expected-error {{closure containing a declaration cannot be used with result builder 'DummyBuilder'}}
+  var observedVar: Int = 123 { // expected-error {{cannot declare local observed variable in result builder}}
     didSet {}
   }
 
   ()
 }
 
 dummy {
-  var observedVar: Int = 123 { // expected-error {{closure containing a declaration cannot be used with result builder 'DummyBuilder'}}
+  var observedVar: Int = 123 { // expected-error {{cannot declare local observed variable in result builder}}
     willSet {}
   }