[Sema] Fix compiler crasher SR-10696

(cherry picked from commit f4c0bc7)

Author: hamishknight

lib/Sema/CSDiag.cpp

@@ -4716,7 +4716,11 @@ static bool isViableOverloadSet(const CalleeCandidateInfo &CCI,
   for (unsigned i = 0; i < CCI.size(); ++i) {
     auto &&cand = CCI[i];
     auto funcDecl = dyn_cast_or_null<AbstractFunctionDecl>(cand.getDecl());
-    if (!funcDecl)
+
+    // If we don't have a func decl or we haven't resolved its parameters,
+    // continue. The latter case can occur with `type(of:)`, which is introduced
+    // as a type variable.
+    if (!funcDecl || !cand.hasParameters())
       continue;
 
     auto params = cand.getParameters();

test/Constraints/type_of.swift

@@ -78,3 +78,9 @@ func bar() -> UInt {}   // expected-note {{found this candidate}}
 foo(type(of: G.T.self)) // Ok
 let _: Any = type(of: G.T.self) // Ok
 foo(type(of: bar())) // expected-error {{ambiguous use of 'bar()'}}
+
+struct SR10696 {
+  func bar(_ s: SR10696.Type) {
+    type(of: s)() // expected-error {{cannot invoke value of type 'SR10696.Type.Type' with argument list '()'}}
+  }
+}