[lldb] Make SBTarget::LaunchSimple start form the target's LaunchInfo

Currently SBTarget::LaunchSimple creates a new LaunchInfo which means it
ignores any target properties that have been set. Instead, it should
start from the target's LaunchInfo and populated the specified fields.

Differential revision: https://reviews.llvm.org/D85235

lldb/test/API/python_api/target/TestTargetAPI.py

@@ -150,6 +150,38 @@ class TargetAPITestCase(TestBase):
         self.assertTrue(error.Success(), "Make sure memory read succeeded")
         self.assertEqual(len(content), 1)
 
+
+    @add_test_categories(['pyapi'])
+    def test_launch_simple(self):
+        d = {'EXE': 'b.out'}
+        self.build(dictionary=d)
+        self.setTearDownCleanup(dictionary=d)
+        target = self.create_simple_target('b.out')
+
+        process = target.LaunchSimple(
+            ['foo', 'bar'], ['baz'], self.get_process_working_directory())
+        self.runCmd("run")
+        output = process.GetSTDOUT(9999)
+        self.assertIn('arg: foo', output)
+        self.assertIn('arg: bar', output)
+        self.assertIn('env: baz', output)
+
+        self.runCmd("setting set target.run-args foo")
+        self.runCmd("setting set target.env-vars bar=baz")
+        process = target.LaunchSimple(None, None,
+                                      self.get_process_working_directory())
+        self.runCmd("run")
+        output = process.GetSTDOUT(9999)
+        self.assertIn('arg: foo', output)
+        self.assertIn('env: bar=baz', output)
+
+        self.runCmd("settings set target.disable-stdio true")
+        process = target.LaunchSimple(
+            None, None, self.get_process_working_directory())
+        self.runCmd("run")
+        output = process.GetSTDOUT(9999)
+        self.assertEqual(output, "")
+
     def create_simple_target(self, fn):
         exe = self.getBuildArtifact(fn)
         target = self.dbg.CreateTarget(exe)