Add a test for preserving state on the non-expr thread across expression evaluation.

There may be another test that tests this but I couldn't find one.

lldb/test/API/functionalities/thread/state_after_expression/Makefile

@@ -0,0 +1,6 @@
+CXX_SOURCES := main.cpp
+CFLAGS_EXTRAS := -std=c++11
+
+ENABLE_THREADS := YES
+
+include Makefile.rules

lldb/test/API/functionalities/thread/state_after_expression/TestStateAfterExpression.py

@@ -0,0 +1,53 @@
+"""
+Make sure the stop reason of a thread that did not run
+during an expression is not changed by running the expression
+"""
+
+
+
+import lldb
+import lldbsuite.test.lldbutil as lldbutil
+from lldbsuite.test.lldbtest import *
+
+
+class TestStopReasonAfterExpression(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test_thread_state_after_expr(self):
+        self.build()
+        self.main_source_file = lldb.SBFileSpec("main.cpp")
+        self.do_test()
+
+    def do_test(self):
+        (target, process, thread, bkpt) = lldbutil.run_to_source_breakpoint(self,
+            "Set a breakpoint here", self.main_source_file)
+
+        self.assertEqual(bkpt.GetNumLocations(), 2, "Got two locations")
+
+        # So now thread holds the main thread.  Continue to hit the
+        # breakpoint again on the spawned thread:
+
+        threads = lldbutil.continue_to_breakpoint(process, bkpt)
+        self.assertEqual(len(threads), 1, "Hit the breakpoint the second time")
+        other_thread = threads[0]
+
+        self.assertNotEqual(thread.GetThreadID(), other_thread.GetThreadID(),
+                            "A different thread")
+        # Run an expression ONLY on other_thread.  Don't let thread run:
+        options = lldb.SBExpressionOptions()
+        options.SetTryAllThreads(False)
+        options.SetStopOthers(True)
+
+        result = thread.frames[0].EvaluateExpression('(int) printf("Hello\\n")', options)
+        self.assertTrue(result.GetError().Success(),
+                        "Expression failed: '%s'"%(result.GetError().GetCString()))
+
+        stop_reason = other_thread.GetStopReason()
+
+        self.assertEqual(stop_reason, lldb.eStopReasonBreakpoint,
+                         "Still records stopped at breakpoint: %s"
+                         %(lldbutil.stop_reason_to_str(stop_reason)))
+        self.assertEqual(other_thread.GetStopReasonDataAtIndex(0), 1,
+                         "Still records stopped at right breakpoint")
+

lldb/test/API/functionalities/thread/state_after_expression/main.cpp

@@ -0,0 +1,14 @@
+#include <thread>
+
+void thread_func() {
+  // Set a breakpoint here
+}
+
+int
+main()
+{
+  // Set a breakpoint here
+  std::thread stopped_thread(thread_func);
+  stopped_thread.join();
+  return 0;
+}