[lldb] Fix dwim-print to not delete non-result persistent variables (llvm#85152) (#8428)

`EvaluateExpression` does not always create a new persistent result. If the expression
is a bare persistent variable, then a new persistent result is not created. This means
the caller can't assume a new persistent result is created for each evaluation.
However, `dwim-print` was doing exactly that: assuming a new persistent result for each
evaluation. This resulted in a bug:

```
(lldb) p int $j = 23
(lldb) p $j
(lldb) p $j
```

The first `p $j` would not create a persistent result, and so `dwim-print` would
inadvertently delete `$j`. The second `p $j` would fail.

The fix is to try `expr` as a persistent variable, after trying `expr` as a frame
variable. For persistent variables, this avoids calling `EvaluateExpression`.

Resolves llvm#84806

rdar://124688427
(cherry picked from commit 4da2b54)

(cherry-picked from commit 38b55e1)

Author: kastiglione

lldb/source/Commands/CommandObjectDWIMPrint.cpp

@@ -25,7 +25,6 @@
 #include "lldb/lldb-forward.h"
 #include "lldb/lldb-types.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Support/FormatVariadic.h"
 
 #include <regex>
 
@@ -200,7 +199,17 @@ void CommandObjectDWIMPrint::DoExecute(StringRef command,
   }
   // END SWIFT
 
-  // Second, also lastly, try `expr` as a source expression to evaluate.
+  // Second, try `expr` as a persistent variable.
+  if (expr.starts_with("$"))
+    if (auto *state = target.GetPersistentExpressionStateForLanguage(language))
+      if (auto var_sp = state->GetVariable(expr))
+        if (auto valobj_sp = var_sp->GetValueObject()) {
+          valobj_sp->Dump(result.GetOutputStream(), dump_options);
+          result.SetStatus(eReturnStatusSuccessFinishResult);
+          return;
+        }
+
+  // Third, and lastly, try `expr` as a source expression to evaluate.
   {
     auto *exe_scope = m_exe_ctx.GetBestExecutionContextScope();
     ValueObjectSP valobj_sp;

lldb/test/API/commands/dwim-print/TestDWIMPrint.py

@@ -146,3 +146,15 @@ def test_void_result(self):
             self, "// break here", lldb.SBFileSpec("main.c")
         )
         self.expect("dwim-print (void)15", matching=False, patterns=["(?i)error"])
+
+    def test_preserves_persistent_variables(self):
+        """Test dwim-print does not delete persistent variables."""
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "// break here", lldb.SBFileSpec("main.c")
+        )
+        self.expect("dwim-print int $i = 15")
+        # Run the same expression twice and verify success. This ensures the
+        # first command does not delete the persistent variable.
+        for _ in range(2):
+            self.expect("dwim-print $i", startstr="(int) 15")