[Expressions] Add support of expressions evaluation in some object's context

Summary:
This patch adds support of expression evaluation in a context of some object.
Consider the following example:
```
struct S {
  int a = 11;
  int b = 12;
};

int main() {
  S s;
  int a = 1;
  int b = 2;
  // We have stopped here
  return 0;
}
```
This patch allows to do something like that:
```
lldb.frame.FindVariable("s").EvaluateExpression("a + b")
```
and the result will be `33` (not `3`) because fields `a` and `b` of `s` will be
used (not locals `a` and `b`).

This is achieved by replacing of `this` type and object for the expression. This
has some limitations: an expression can be evaluated only for values located in
the debuggee process memory (they must have an address of `eAddressTypeLoad`
type).

Reviewers: teemperor, clayborg, jingham, zturner, labath, davide, spyffe, serge-sans-paille

Reviewed By: jingham

Subscribers: abidh, lldb-commits, leonid.mashinskiy

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D55318

llvm-svn: 353149

1 files changed, 145 insertions, 0 deletions

diff --git a/lldb/packages/Python/lldbsuite/test/expression_command/context-object/TestContextObject.py b/lldb/packages/Python/lldbsuite/test/expression_command/context-object/TestContextObject.py
new file mode 100644
index 00000000000..02b8162aad6
--- /dev/null
+++ b/lldb/packages/Python/lldbsuite/test/expression_command/context-object/TestContextObject.py
@@ -0,0 +1,145 @@
+"""
+Tests expression evaluation in context of an object.
+"""
+
+import lldb
+import lldbsuite.test.lldbutil as lldbutil
+from lldbsuite.test.lldbtest import *
+
+class ContextObjectTestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test_context_object(self):
+        """Tests expression evaluation in context of an object."""
+        self.build()
+
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(self, '// Break here', self.main_source_spec)
+        frame = thread.GetFrameAtIndex(0)
+
+        #
+        # Test C++ struct variable
+        #
+
+        obj_val = frame.FindVariable("cpp_struct")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test an empty expression evaluation
+        value = obj_val.EvaluateExpression("")
+        self.assertFalse(value.IsValid())
+        self.assertFalse(value.GetError().Success())
+
+        # Test retrieveing of a field (not a local with the same name)
+        value = obj_val.EvaluateExpression("field")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 1111)
+
+        # Test functions evaluation
+        value = obj_val.EvaluateExpression("function()")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 2222)
+
+        # Test that we retrieve the right global
+        value = obj_val.EvaluateExpression("global.field")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 1111)
+
+        #
+        # Test C++ union variable
+        #
+
+        obj_val = frame.FindVariable("cpp_union")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test retrieveing of a field
+        value = obj_val.EvaluateExpression("field_int")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 5555)
+
+        #
+        # Test C++ scalar
+        #
+
+        obj_val = frame.FindVariable("cpp_scalar")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test an expression evaluation
+        value = obj_val.EvaluateExpression("1")
+        self.assertFalse(value.IsValid())
+        self.assertFalse(value.GetError().Success())
+
+        #
+        # Test C++ array
+        #
+
+        obj_val = frame.FindVariable("cpp_array")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test an expression evaluation
+        value = obj_val.EvaluateExpression("1")
+        self.assertFalse(value.IsValid())
+        self.assertFalse(value.GetError().Success())
+
+        # Test retrieveing of an element's field
+        value = obj_val.GetValueForExpressionPath("[7]").EvaluateExpression("field")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 1111)
+
+        #
+        # Test C++ pointer
+        #
+
+        obj_val = frame.FindVariable("cpp_pointer")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test an expression evaluation
+        value = obj_val.EvaluateExpression("1")
+        self.assertFalse(value.IsValid())
+        self.assertFalse(value.GetError().Success())
+
+        # Test retrieveing of a dereferenced object's field
+        value = obj_val.Dereference().EvaluateExpression("field")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 1111)
+
+        #
+        # Test C++ computation result
+        #
+
+        obj_val = frame.EvaluateExpression("cpp_namespace::GetCppStruct()")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test an expression evaluation
+        value = obj_val.EvaluateExpression("1")
+        self.assertTrue(value.IsValid())
+        self.assertFalse(value.GetError().Success())
+
+        #
+        # Test C++ computation result located in debuggee memory
+        #
+
+        obj_val = frame.EvaluateExpression("cpp_namespace::GetCppStructPtr()")
+        self.assertTrue(obj_val.IsValid())
+
+        # Test an expression evaluation
+        value = obj_val.EvaluateExpression("1")
+        self.assertFalse(value.IsValid())
+        self.assertFalse(value.GetError().Success())
+
+        # Test retrieveing of a dereferenced object's field
+        value = obj_val.Dereference().EvaluateExpression("field")
+        self.assertTrue(value.IsValid())
+        self.assertTrue(value.GetError().Success())
+        self.assertEqual(value.GetValueAsSigned(), 1111)
+
+    def setUp(self):
+        TestBase.setUp(self)
+
+        self.main_source = "main.cpp"
+        self.main_source_spec = lldb.SBFileSpec(self.main_source)