[Sema] Diagnose invalid $ prefixes on closure parameters after the

closure is resolved. This can't be diagnosed earlier because a property
wrapper attribute may be inferred in the constraint system.

Author: hborla

include/swift/AST/Identifier.h

@@ -166,7 +166,7 @@ class Identifier {
   }
 
   bool hasDollarPrefix() const {
-    return str().startswith("$");
+    return str().startswith("$") && !(getLength() == 1);
   }
 
   const void *getAsOpaquePointer() const {

lib/Sema/TypeCheckStmt.cpp

@@ -40,6 +40,7 @@
 #include "swift/Basic/TopCollection.h"
 #include "swift/Parse/Lexer.h"
 #include "swift/Parse/LocalContext.h"
+#include "swift/Parse/Parser.h"
 #include "swift/Sema/IDETypeChecking.h"
 #include "swift/Syntax/TokenKinds.h"
 #include "llvm/ADT/DenseMap.h"
@@ -2080,6 +2081,13 @@ bool TypeChecker::typeCheckClosureBody(ClosureExpr *closure) {
   TypeChecker::checkClosureAttributes(closure);
   TypeChecker::checkParameterList(closure->getParameters(), closure);
 
+  for (auto *param : *closure->getParameters()) {
+    if (!param->isImplicit() && param->getName().hasDollarPrefix() &&
+        !param->hasAttachedPropertyWrapper()) {
+      param->diagnose(diag::dollar_identifier_decl, param->getName());
+    }
+  }
+
   BraceStmt *body = closure->getBody();
 
   Optional<FunctionBodyTimer> timer;

test/Parse/dollar_identifier.swift

@@ -77,9 +77,12 @@ func $declareWithDollar() { // expected-error{{cannot declare entity named '$dec
     $b c: Int) { } // expected-error{{cannot declare entity named '$b'}}
   let _: (Int) -> Int = {
     [$capture = 0] // expected-error{{cannot declare entity named '$capture'}}
-    $a in // expected-error{{cannot declare entity named '$a'}}
+    $a in // diagnosed after type checking the closure
     $capture
   }
+  let _: (Int) -> Void = {
+    $a in // expected-error{{cannot declare entity named '$a'}}
+  }
   let ($a: _, _) = (0, 0) // expected-error{{cannot declare entity named '$a'}}
   $label: if true { // expected-error{{cannot declare entity named '$label'}}
     break $label