Improve the data formatter UX if an array is uninitialized.

Global variables in Swift are lazy initialized and often zeroed out
before the first access. This can be confusing to users, so this patch
modifies the array dataformatter to recognize a null array.

rdar://132736658

Author: adrian-prantl

lldb/source/Plugins/Language/Swift/SwiftArray.cpp

@@ -114,7 +114,7 @@ SwiftArrayNativeBufferHandler::SwiftArrayNativeBufferHandler(
 }
 
 bool SwiftArrayNativeBufferHandler::IsValid() {
-  return m_metadata_ptr != LLDB_INVALID_ADDRESS &&
+  return m_metadata_ptr != LLDB_INVALID_ADDRESS && m_metadata_ptr &&
          m_first_elem_ptr != LLDB_INVALID_ADDRESS && m_capacity >= m_size &&
          m_elem_type.IsValid();
 }
@@ -437,10 +437,7 @@ SwiftArrayBufferHandler::CreateBufferHandler(ValueObject &static_valobj) {
         handler.reset(new SwiftArrayBridgedBufferHandler(
             process_sp, masked_storage_location));
       }
-
-      if (handler && handler->IsValid())
-        return handler;
-      return nullptr;
+      return handler;
     } else {
       CompilerType elem_type(
           valobj.GetCompilerType().GetArrayElementType(exe_scope));
@@ -457,6 +454,12 @@ bool lldb_private::formatters::swift::Array_SummaryProvider(
   if (!handler)
     return false;
 
+  if (!handler->IsValid()) {
+    // FIXME: This should be an out-of-band llvm::Error return value.
+    stream << "<uninitialized>";
+    return true;
+  }
+
   auto count = handler->GetCount();
 
   stream.Printf("%zu value%s", count, (count == 1 ? "" : "s"));

lldb/test/API/lang/swift/array_uninitialized/Makefile

@@ -0,0 +1,3 @@
+SWIFT_SOURCES := main.swift
+SWIFTFLAGS_EXTRAS := -parse-as-library
+include Makefile.rules

lldb/test/API/lang/swift/array_uninitialized/TestSwiftArrayUninitialized.py

@@ -0,0 +1,15 @@
+import lldb
+from lldbsuite.test.decorators import *
+import lldbsuite.test.lldbtest as lldbtest
+import lldbsuite.test.lldbutil as lldbutil
+
+
+class TestSwiftArrayUninitialized(lldbtest.TestBase):
+    @swiftTest
+    def test(self):
+        """Test unitialized global arrays"""
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, 'break here', lldb.SBFileSpec('main.swift'))
+        self.expect("target variable -- array_unused", substrs=['<uninitialized>'])
+        self.expect("target variable -- array_used_empty", substrs=['0 values'])

lldb/test/API/lang/swift/array_uninitialized/main.swift

@@ -0,0 +1,8 @@
+var array_unused : [Int] = [1,2,3]
+var array_used_empty : [Int] = []
+@main struct Main {
+  static func main() {
+    print(array_used_empty)
+    print("break here")
+  }
+}

lldb/test/API/lang/swift/nsarray_code_running_formatter/main.swift

@@ -23,7 +23,7 @@ func main() {
   var tb = Test() as Array + []
 
   print("second stop") //% self.expect('frame variable -d run -- t', substrs=['t = 0x', 'NSArray = {', 'NSObject = {'])
-                       //% self.expect('frame variable -d run -- ta', substrs=['ta = {', '_buffer = {', '_storage =', 'rawValue = 0x'])
+                       //% self.expect('frame variable -d run -- ta', substrs=['ta = <uninitialized>', '_buffer = {', '_storage =', 'rawValue = 0x'])
                        //% self.expect('frame variable -d run -- tb', substrs=['tb = 1 value {', '"abc"'])
                        //% self.expect('po t', substrs=['0 : abc'])
                        //% self.expect('po ta', substrs=['0 : abc'])