[CSDiagnostics] Tailor diagnostic for define missing member when involves array literal and unresolved member

Author: LucianoPAlmeida

lib/Sema/CSDiagnostics.cpp

@@ -3212,6 +3212,9 @@ bool MissingMemberFailure::diagnoseAsError() {
 
   if (diagnoseForDynamicCallable())
     return true;
+  
+  if (diagnoseForDefaultAnyArrayLiteral())
+    return true;
 
   auto baseType = resolveType(getBaseType())->getWithoutSpecifierType();
 
@@ -3399,6 +3402,29 @@ bool MissingMemberFailure::diagnoseForDynamicCallable() const {
   return false;
 }
 
+bool MissingMemberFailure::diagnoseForDefaultAnyArrayLiteral() const {
+  auto &cs = getConstraintSystem();
+  auto *expr = getAsExpr(getAnchor());
+  auto *parentExpr = cs.getParentExpr(expr);
+  auto contextualType = getContextualType(parentExpr);
+  auto baseType = resolveType(getBaseType())->getWithoutSpecifierType();
+
+  if (contextualType)
+    return false;
+  
+  if (isa<UnresolvedMemberExpr>(expr) && isa<ArrayExpr>(parentExpr)) {
+    if (auto *metatype = baseType->getAs<MetatypeType>()) {
+      baseType = metatype->getInstanceType();
+    }
+    
+    if (baseType->isAny()) {
+      emitDiagnostic(diag::unresolved_member_no_inference, getName());
+      return true;
+    }
+  }
+  return false;
+}
+
 bool InvalidMemberRefOnExistential::diagnoseAsError() {
   auto anchor = getRawAnchor();
 

lib/Sema/CSDiagnostics.h

@@ -1059,6 +1059,10 @@ class MissingMemberFailure final : public InvalidMemberRefFailure {
   /// overload to be present, but a class marked as `@dynamicCallable`
   /// defines only `dynamicallyCall(withArguments:)` variant.
   bool diagnoseForDynamicCallable() const;
+  
+  /// Tailored diagnostics for array literal with unresolved member expression
+  /// that defaults the element to element type. e.g. _ = [.e]
+  bool diagnoseForDefaultAnyArrayLiteral() const;
 
   static DeclName findCorrectEnumCaseName(Type Ty,
                                           TypoCorrectionResults &corrections,