Merge pull request #4680 from rudkx/rdar27449208-swift-3.0-branch

Special-case error for indexing into a nil literal.

Author: tkremenek

include/swift/AST/DiagnosticsSema.def

@@ -196,6 +196,9 @@ ERROR(cannot_subscript_base,none,
       "cannot subscript a value of type %0",
       (Type))
 
+ERROR(cannot_subscript_nil_literal,none,
+      "cannot subscript a nil literal value", ())
+
 ERROR(cannot_pass_rvalue_inout_subelement,none,
       "cannot pass immutable value as inout argument: %0",
       (StringRef))

lib/Sema/CSDiag.cpp

@@ -4762,6 +4762,12 @@ bool FailureDiagnosis::visitSubscriptExpr(SubscriptExpr *SE) {
   if (!baseExpr) return true;
   auto baseType = baseExpr->getType();
 
+  if (isa<NilLiteralExpr>(baseExpr)) {
+    diagnose(baseExpr->getLoc(), diag::cannot_subscript_nil_literal)
+      .highlight(baseExpr->getSourceRange());
+    return true;
+  }
+
   auto locator =
     CS->getConstraintLocator(SE, ConstraintLocator::SubscriptMember);
 

test/decl/subscript/subscripting.swift

@@ -254,6 +254,9 @@ func testSubscript1(_ s2 : SubscriptTest2) {
 
 
   let b = s2[1, "foo"] // expected-error {{cannot convert value of type 'Int' to expected argument type 'String'}}
+
+  // rdar://problem/27449208
+  let v: (Int?, [Int]?) = (nil [17]) // expected-error {{cannot subscript a nil literal value}}
 }
 
 // sr-114 & rdar://22007370