Merge pull request #30621 from xedin/extend-nil-diags

[ConstraintSystem] Diagnose more cases of invalid `nil` use during co…

Author: xedin

lib/Sema/CSGen.cpp

@@ -1155,7 +1155,18 @@ namespace {
       while (parentExpr && isa<ParenExpr>(parentExpr))
         parentExpr = CS.getParentExpr(parentExpr);
 
+      // In cases like `_ = nil?` AST would have `nil`
+      // wrapped in `BindOptionalExpr`.
+      if (parentExpr && isa<BindOptionalExpr>(parentExpr))
+        parentExpr = CS.getParentExpr(parentExpr);
+
       if (parentExpr) {
+        // `_ = nil as? ...`
+        if (isa<ConditionalCheckedCastExpr>(parentExpr)) {
+          DE.diagnose(expr->getLoc(), diag::conditional_cast_from_nil);
+          return Type();
+        }
+
         // `_ = nil!`
         if (isa<ForceValueExpr>(parentExpr)) {
           DE.diagnose(expr->getLoc(), diag::cannot_force_unwrap_nil_literal);
@@ -1167,13 +1178,13 @@ namespace {
           DE.diagnose(expr->getLoc(), diag::unresolved_nil_literal);
           return Type();
         }
-      }
 
-      // `_ = nil`
-      if (auto *assignment = dyn_cast_or_null<AssignExpr>(parentExpr)) {
-        if (isa<DiscardAssignmentExpr>(assignment->getDest())) {
-          DE.diagnose(expr->getLoc(), diag::unresolved_nil_literal);
-          return Type();
+        // `_ = nil`
+        if (auto *assignment = dyn_cast<AssignExpr>(parentExpr)) {
+          if (isa<DiscardAssignmentExpr>(assignment->getDest())) {
+            DE.diagnose(expr->getLoc(), diag::unresolved_nil_literal);
+            return Type();
+          }
         }
       }
 
@@ -2982,26 +2993,6 @@ namespace {
       if (!fromExpr) // Either wasn't constructed correctly or wasn't folded.
         return nullptr;
 
-      std::function<Expr *(Expr *)> nilLiteralExpr = [&](Expr *expr) -> Expr * {
-        expr = expr->getSemanticsProvidingExpr();
-        if (expr->getKind() == ExprKind::NilLiteral)
-          return expr;
-
-        if (auto *optionalEvalExpr = dyn_cast<OptionalEvaluationExpr>(expr))
-          return nilLiteralExpr(optionalEvalExpr->getSubExpr());
-
-        if (auto *bindOptionalExpr = dyn_cast<BindOptionalExpr>(expr))
-          return nilLiteralExpr(bindOptionalExpr->getSubExpr());
-
-        return nullptr;
-      };
-
-      if (auto nilLiteral = nilLiteralExpr(fromExpr)) {
-        ctx.Diags.diagnose(nilLiteral->getLoc(),
-                           diag::conditional_cast_from_nil);
-        return nullptr;
-      }
-
       // Validate the resulting type.
       TypeResolutionOptions options(TypeResolverContext::ExplicitCastExpr);
       options |= TypeResolutionFlags::AllowUnboundGenerics;

test/Constraints/casts.swift

@@ -221,7 +221,7 @@ func process(p: Any?) {
 func compare<T>(_: T, _: T) {} // expected-note {{'compare' declared here}}
 func compare<T>(_: T?, _: T?) {}
 
-_ = nil? as? Int?? // expected-error {{nil literal cannot be the source of a conditional cast}}
+_ = nil? as? Int?? // expected-error {{'nil' requires a contextual type}}
 
 func test_tuple_casts_no_warn() {
   struct Foo {}

test/Constraints/optional.swift

@@ -439,9 +439,10 @@ func sr_12309() {
   _ = (nil!) // expected-error {{'nil' literal cannot be force unwrapped}}
   _ = (nil)! // expected-error {{'nil' literal cannot be force unwrapped}}
   _ = ((nil))! // expected-error {{'nil' literal cannot be force unwrapped}}
-  _ = nil? // expected-error {{value of optional type 'Optional<_>' must be unwrapped to a value of type '_'}}
-           // expected-note@-1 {{coalesce using '??' to provide a default when the optional value contains 'nil'}}
-           // expected-note@-2 {{force-unwrap using '!' to abort execution if the optional value contains 'nil'}}
+  _ = nil? // expected-error {{'nil' requires a contextual type}}
+  _ = ((nil?)) // expected-error {{'nil' requires a contextual type}}
+  _ = ((nil))? // expected-error {{'nil' requires a contextual type}}
+  _ = ((nil)?) // expected-error {{'nil' requires a contextual type}}
   _ = nil // expected-error {{'nil' requires a contextual type}}
   _ = (nil) // expected-error {{'nil' requires a contextual type}}
   _ = ((nil)) // expected-error {{'nil' requires a contextual type}}