Merge pull request #16166 from slavapestov/if-expr-crash

Sema: Fix crash in IfExpr diagnostics

Author: slavapestov

lib/Sema/CSApply.cpp

@@ -8468,6 +8468,11 @@ Solution::convertBooleanTypeToBuiltinI1(Expr *expr,
 
   auto type = cs.getType(expr);
 
+  // We allow UnresolvedType <c $T for all $T, so we might end up here
+  // in diagnostics. Just bail out.
+  if (type->is<UnresolvedType>())
+    return expr;
+
   // Look for the builtin name. If we don't have it, we need to call the
   // general name via the witness table.
   NameLookupOptions lookupOptions = defaultMemberLookupOptions;

test/Constraints/if_expr.swift

@@ -63,3 +63,25 @@ let ib: Bool! = false
 let eb: Bool? = .some(false)
 let conditional = ib ? "Broken" : "Heart" // should infer Bool!
 let conditional = eb ? "Broken" : "Heart" // expected-error {{value of optional type 'Bool?' not unwrapped; did you mean to use '!' or '?'?}}
+
+// <rdar://problem/39586166> - crash when IfExpr has UnresolvedType in condition
+struct Delegate {
+  var shellTasks: [ShellTask]
+}
+
+extension Array {
+  subscript(safe safe: Int) -> Element? { // expected-note {{found this candidate}}
+    get { }
+    set { }
+  }
+}
+
+struct ShellTask {
+  var commandLine: [String]
+}
+
+let delegate = Delegate(shellTasks: [])
+_ = delegate.shellTasks[safe: 0]?.commandLine.compactMap({ $0.asString.hasPrefix("") ? $0 : nil }).count ?? 0
+// expected-error@-1 {{ambiguous reference to member 'subscript'}}
+
+// FIXME: Horrible diagnostic, but at least we no longer crash