Add Swift specific test

Author: kastiglione

lldb/test/API/commands/expression/persistent_result/swift/Makefile

@@ -0,0 +1,3 @@
+SWIFT_SOURCES := main.swift
+
+include Makefile.rules

lldb/test/API/commands/expression/persistent_result/swift/TestSwiftPersistentResult.py

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+"""
+Test controlling `expression` result variables are persistent.
+"""
+
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test.decorators import *
+from lldbsuite.test import lldbutil
+
+
+class TestCase(TestBase):
+    def setUp(self):
+        TestBase.setUp(self)
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "break here", lldb.SBFileSpec("main.swift"))
+
+    def test_enable_persistent_result(self):
+        """Test explicitly enabling result variables persistence."""
+        self.expect("expression --persistent-result on -- i", startstr="(Int) $R0 = 30")
+        # Verify the lifetime of $R0 extends beyond the `expression` it was created in.
+        self.expect("expression $R0", startstr="(Int) $R1 = 30")
+
+    def test_disable_persistent_result(self):
+        """Test explicitly disabling persistent result variables."""
+        self.expect("expression --persistent-result off -- i", startstr="(Int) 30")
+        # Verify a persistent result was not silently created.
+        self.expect("expression $R0", error=True)
+
+    def test_expression_persists_result(self):
+        """Test `expression`'s default behavior is to persist a result variable."""
+        self.expect("expression i", startstr="(Int) $R0 = 30")
+        self.expect("expression $R0", startstr="(Int) $R1 = 30")
+
+    def test_p_does_not_persist_results(self):
+        """Test `p` does not persist a result variable."""
+        self.expect("p i", startstr="(Int) 30")
+        self.expect("p $R0", error=True)

lldb/test/API/commands/expression/persistent_result/swift/main.swift

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+func main() {
+  var i = 30
+  print("break here")
+}
+
+main()