Sema: Fix code completion crash when a ParamDecl hasn't had its type set yet

We set the type of ParamDecls when applying solutions in the normal path, but
sometimes code completion will type check an expression inside a closure without
checking the outer expression. In this case, we may have inferred a type for
the ParamDecl, but we don't write it back.

Instead, just look at the DeclRefExpr's type.

Fixes <rdar://problem/42098113>.

Author: slavapestov

lib/Sema/MiscDiagnostics.cpp

@@ -584,7 +584,7 @@ static void diagSyntacticUseRestrictions(TypeChecker &TC, const Expr *E,
     void checkNoEscapeParameterUse(DeclRefExpr *DRE, Expr *parent,
                                    OperandKind useKind) {
       // This only cares about declarations of noescape function type.
-      auto AFT = DRE->getDecl()->getInterfaceType()->getAs<AnyFunctionType>();
+      auto AFT = DRE->getType()->getAs<FunctionType>();
       if (!AFT || !AFT->isNoEscape())
         return;
 

validation-test/IDE/crashers_2_fixed/rdar42098113.swift

@@ -0,0 +1,8 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=A -source-filename %s
+
+func test() {
+  let cl = { arg in
+    let name = arg as String
+    #^A^#
+  }
+}