[lldb] Fix crash after second run when set a previous watchpoint.

Author: hapeeeeee

lldb/source/Breakpoint/Watchpoint.cpp

@@ -409,6 +409,15 @@ bool Watchpoint::IsDisabledDuringEphemeralMode() {
 }
 
 void Watchpoint::SetEnabled(bool enabled, bool notify) {
+  // Whenever setting the enabled state of a watchpoint, we need to ensure
+  // that `m_new_value_sp` exists to avoid crash when reading old_data later.
+  // See https://github.com/llvm/llvm-project/issues/135590.
+  if (!m_new_value_sp) {
+    ExecutionContext exe_ctx;
+    m_target.GetProcessSP()->CalculateExecutionContext(exe_ctx);
+    CaptureWatchedValue(exe_ctx);
+  }
+
   if (!enabled) {
     if (m_is_ephemeral)
       ++m_disabled_count;

lldb/test/Shell/Watchpoint/ReuseWatchpointAfterReExecProcess.test

@@ -0,0 +1,21 @@
+# RUN: %clangxx_host %p/Inputs/languages.cpp -g -o %t.out
+# RUN: %lldb -b -o 'settings set interpreter.stop-command-source-on-error false' -s %s %t.out 2>&1 | FileCheck %s
+
+b main
+run
+# CHECK: stopped
+# CHECK-NEXT: stop reason = breakpoint
+
+watchpoint set variable val
+# CHECK: Watchpoint created:
+
+kill
+run
+# CHECK: stopped
+# CHECK-NEXT: stop reason = breakpoint
+
+watchpoint set variable val
+# CHECK: Watchpoint created:
+
+continue
+# CHECK: Watchpoint 1 hit: