[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, 15 insertions, 3 deletions

diff --git a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.h b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.h
index 836d44e7544..2f9a7238b4c 100644
--- a/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.h
+++ b/lldb/source/Plugins/ExpressionParser/Clang/ClangUserExpression.h
@@ -61,7 +61,8 @@ public:
 
     void ResetDeclMap(ExecutionContext &exe_ctx,
                       Materializer::PersistentVariableDelegate &result_delegate,
-                      bool keep_result_in_memory);
+                      bool keep_result_in_memory,
+                      ValueObject *ctx_obj);
 
     //------------------------------------------------------------------
     /// Return the object that the parser should allow to access ASTs. May be
@@ -105,11 +106,17 @@ public:
   /// @param[in] desired_type
   ///     If not eResultTypeAny, the type to use for the expression
   ///     result.
+  ///
+  /// @param[in] ctx_obj
+  ///     The object (if any) in which context the expression
+  ///     must be evaluated. For details see the comment to
+  ///     `UserExpression::Evaluate`.
   //------------------------------------------------------------------
   ClangUserExpression(ExecutionContextScope &exe_scope, llvm::StringRef expr,
                       llvm::StringRef prefix, lldb::LanguageType language,
                       ResultType desired_type,
-                      const EvaluateExpressionOptions &options);
+                      const EvaluateExpressionOptions &options,
+                      ValueObject *ctx_obj);
 
   ~ClangUserExpression() override;
 
@@ -153,7 +160,8 @@ public:
                     Materializer::PersistentVariableDelegate &result_delegate,
                     bool keep_result_in_memory) {
     m_type_system_helper.ResetDeclMap(exe_ctx, result_delegate,
-                                      keep_result_in_memory);
+                                      keep_result_in_memory,
+                                      m_ctx_obj);
   }
 
   lldb::ExpressionVariableSP
@@ -204,6 +212,10 @@ private:
   /// were not able to calculate this position.
   llvm::Optional<size_t> m_user_expression_start_pos;
   ResultDelegate m_result_delegate;
+
+  /// The object (if any) in which context the expression is evaluated.
+  /// See the comment to `UserExpression::Evaluate` for details.
+  ValueObject *m_ctx_obj;
 };
 
 } // namespace lldb_private