[lldb] Allow "var" persistent variables to be modified

lldb/source/Plugins/ExpressionParser/Swift/SwiftExpressionParser.cpp

@@ -1633,14 +1633,10 @@ unsigned SwiftExpressionParser::Parse(DiagnosticManager &diagnostic_manager,
 
       swift::VarDecl *decl = variable_info.GetDecl();
       if (decl) {
-        if (decl->isLet()) {
-          llvm::cast<SwiftExpressionVariable>(persistent_variable.get())
-              ->SetIsModifiable(false);
-        }
-        if (!decl->hasStorage()) {
-          llvm::cast<SwiftExpressionVariable>(persistent_variable.get())
-              ->SetIsComputed(true);
-        }
+        auto swift_var =
+            llvm::cast<SwiftExpressionVariable>(persistent_variable.get());
+        swift_var->SetIsModifiable(!decl->isLet());
+        swift_var->SetIsComputed(!decl->hasStorage());
       }
 
       variable_info.m_metadata.reset(

lldb/test/API/lang/swift/expression/mutable_persistent_var/Makefile

@@ -0,0 +1,2 @@
+SWIFT_SOURCES := main.swift
+include Makefile.rules

lldb/test/API/lang/swift/expression/mutable_persistent_var/TestSwiftMutablePersistentVar.py

@@ -0,0 +1,14 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+import lldbsuite.test.lldbutil as lldbutil
+
+
+class TestCase(TestBase):
+    @swiftTest
+    def test(self):
+        """Test that persistent variables are mutable."""
+        self.build()
+        lldbutil.run_to_name_breakpoint(self, "main")
+        self.expect("expr var $count = 30")
+        self.expect("expr $count = 41")

lldb/test/API/lang/swift/expression/mutable_persistent_var/main.swift

@@ -0,0 +1 @@
+// does nothing