Make sure to hide constructors with underscored API names as private stdlib symbols. (#2839)

This completely removes 'Builtin.<type>' from the interface.
The changes in stdlib interface were reviewed by Dmitri.

Author: akyrtzi

lib/AST/Decl.cpp

@@ -425,6 +425,9 @@ bool Decl::isPrivateStdlibDecl(bool whitelistProtocols) const {
     for (auto param : *params) {
       if (param->hasName() && param->getNameStr().startswith("_"))
         return true;
+      auto argName = param->getArgumentName();
+      if (!argName.empty() && argName.str().startswith("_"))
+        return true;
     }
     return false;
   };

stdlib/public/core/FixedPoint.swift.gyb

@@ -243,11 +243,11 @@ public struct ${Self}
 % if self_ty.is_word:
   @_transparent
   public // @testable
-  init(_ v: Builtin.Word) {
+  init(_ _v: Builtin.Word) {
 % if BuiltinName == 'Int32':
-    self._value = Builtin.truncOrBitCast_Word_Int32(v)
+    self._value = Builtin.truncOrBitCast_Word_Int32(_v)
 % elif BuiltinName == 'Int64':
-    self._value = Builtin.zextOrBitCast_Word_Int64(v)
+    self._value = Builtin.zextOrBitCast_Word_Int64(_v)
 % end
   }
 

test/IDE/print_stdlib.swift

@@ -33,8 +33,8 @@
 // DONT_CHECK-NOT: {{([^I]|$)([^n]|$)([^d]|$)([^e]|$)([^x]|$)([^a]|$)([^b]|$)([^l]|$)([^e]|$)}}
 // CHECK-NOT: buffer: _ArrayBuffer
 // CHECK-NOT: func ~>
-// FIXME: Builtin.
-// FIXME: RawPointer
+// CHECK-NOT: Builtin.
+// CHECK-NOT: RawPointer
 // CHECK-NOT: extension [
 // CHECK-NOT: extension {{.*}}?
 // CHECK-NOT: extension {{.*}}!