[Lldb-commits] [lldb] WIP: [lldb] Support Persistent Variables as DIL Identifiers (PR #215706)

[Will Hawkins via lldb-commits]

https://github.com/hawkinsw created https://github.com/llvm/llvm-project/pull/215706

When a persistent variable is used in a DIL expression, look it up as if it were any other identifier.

>From 0c9cc2ee7ba5a383b7cc8e4bce2fafc33d504806 Mon Sep 17 00:00:00 2001
From: Will Hawkins <hawkinsw at obs.cr>
Date: Tue, 11 Aug 2026 21:46:30 -0400
Subject: [PATCH] WIP: [lldb] Support Persistent Variables as DIL Identifiers

When a persistent variable is used in a DIL expression, look it up as if
it were any other identifier.

Signed-off-by: Will Hawkins <hawkinsw at obs.cr>
---
 lldb/include/lldb/ValueObject/DILEval.h |  7 +++++
 lldb/source/ValueObject/DILEval.cpp     | 37 +++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/lldb/include/lldb/ValueObject/DILEval.h b/lldb/include/lldb/ValueObject/DILEval.h
index 489dc801b20db..3a873063adda1 100644
--- a/lldb/include/lldb/ValueObject/DILEval.h
+++ b/lldb/include/lldb/ValueObject/DILEval.h
@@ -18,6 +18,13 @@
 
 namespace lldb_private::dil {
 
+/// Given the name of a persistent identifier (i.e., one that starts with a $),
+/// find the ValueObject for that name (if it exists).
+lldb::ValueObjectSP LookupPersistentIdentifier(llvm::StringRef name_ref,
+                                               StackFrame &stack_frame,
+                                               lldb::TargetSP target_sp,
+                                               lldb::LanguageType language);
+
 /// Given the name of an identifier (variable name, member name, type name,
 /// etc.), find the ValueObject for that name (if it exists), excluding global
 /// variables, and create and return an IdentifierInfo object containing all
diff --git a/lldb/source/ValueObject/DILEval.cpp b/lldb/source/ValueObject/DILEval.cpp
index 0ef4e244410a4..da7c7eaac16ac 100644
--- a/lldb/source/ValueObject/DILEval.cpp
+++ b/lldb/source/ValueObject/DILEval.cpp
@@ -8,16 +8,20 @@
 
 #include "lldb/ValueObject/DILEval.h"
 #include "lldb/Core/Module.h"
+#include "lldb/Expression/ExpressionVariable.h"
 #include "lldb/Symbol/CompileUnit.h"
 #include "lldb/Symbol/TypeSystem.h"
 #include "lldb/Symbol/VariableList.h"
 #include "lldb/Target/RegisterContext.h"
+#include "lldb/Target/Target.h"
 #include "lldb/Utility/LLDBLog.h"
 #include "lldb/ValueObject/DILAST.h"
 #include "lldb/ValueObject/DILParser.h"
 #include "lldb/ValueObject/ValueObject.h"
 #include "lldb/ValueObject/ValueObjectRegister.h"
 #include "lldb/ValueObject/ValueObjectVariable.h"
+#include "lldb/lldb-enumerations.h"
+#include "lldb/lldb-private-types.h"
 #include "llvm/Support/ErrorExtras.h"
 #include "llvm/Support/FormatAdapters.h"
 #include <memory>
@@ -44,6 +48,17 @@ static lldb::ValueObjectSP ArrayToPointerConversion(ValueObject &valobj,
       /* do_deref */ false);
 }
 
+static llvm::Expected<lldb::LanguageType>
+GetSourceLanguageFromCU(StackFrame &ctx) {
+  SymbolContext symbol_context =
+      ctx.GetSymbolContext(lldb::eSymbolContextCompUnit);
+  if (!symbol_context.comp_unit)
+    return llvm::createStringErrorV("no compile unit for frame: {}",
+                                    ctx.GetFunctionName());
+
+  return symbol_context.comp_unit->GetLanguage();
+}
+
 static llvm::Expected<lldb::TypeSystemSP> GetTypeSystemFromCU(StackFrame &ctx) {
   SymbolContext symbol_context =
       ctx.GetSymbolContext(lldb::eSymbolContextCompUnit);
@@ -323,6 +338,20 @@ lldb::ValueObjectSP LookupGlobalIdentifier(llvm::StringRef name_ref,
   return nullptr;
 }
 
+lldb::ValueObjectSP LookupPersistentIdentifier(llvm::StringRef name_ref,
+                                               StackFrame &stack_frame,
+                                               lldb::TargetSP target_sp,
+                                               lldb::LanguageType language) {
+  if (name_ref.starts_with("$")) {
+    if (auto *state =
+            target_sp->GetPersistentExpressionStateForLanguage(language))
+      if (auto var_sp = state->GetVariable(name_ref))
+        if (auto valobj_sp = var_sp->GetValueObject())
+          return valobj_sp;
+  }
+  return nullptr;
+}
+
 lldb::ValueObjectSP LookupIdentifier(llvm::StringRef name_ref,
                                      StackFrame &stack_frame,
                                      lldb::DynamicValueType use_dynamic) {
@@ -459,6 +488,14 @@ Interpreter::Visit(const IdentifierNode &node) {
   if (!identifier)
     identifier = LookupEnumValue(node.GetName(), m_stack_frame);
 
+  if (!identifier && node.GetName()[0] == '$') {
+    auto language = GetSourceLanguageFromCU(m_stack_frame);
+    if (!language)
+      return language.takeError();
+    identifier = LookupPersistentIdentifier(node.GetName(), m_stack_frame,
+                                            m_target, language.get());
+  }
+
   if (!identifier && node.GetName() == "nullptr") {
     // If we got a "nullptr" identifier, and there is no defined variable with
     // this name, resolve it as a null pointer.