[lldb] Fix missing characters when autocompleting LLDB commands in REPL

lldb/test/API/lang/swift/completion/TestSwiftREPLCompletion.py

@@ -35,6 +35,51 @@ def test_basic_completion(self):
         self.child.expect_exact("Hasher")
         self.child.sendline("")
 
+        self.quit()
+
+    # PExpect uses many timeouts internally and doesn't play well
+    # under ASAN on a loaded machine..
+    @skipIfAsan
+    @skipUnlessDarwin
+    def test_lldb_command_completion(self):
+
+        self.launch(extra_args=["--repl"], executable=None, dimensions=(100,500))
+
+        # Wait on the first prompt
+        self.child.expect_exact("1>")
+
+        # Try completing something already complete.
+        self.child.send(":b\t")
+        self.child.expect_exact(":b ")
+        self.child.sendline("")
+
+        # Try completing something that only has one result "vers" -> "version".
+        self.child.send(":vers\t")
+        self.child.expect_exact(":version")
+        self.child.sendline("")
+
+        # Try completing something that has multiple completions.
+        self.child.send(":\t")
+        self.child.expect_exact("Available completions:")
+        self.child.expect_exact(":help")
+        self.child.expect_exact("More (Y/n/a)")
+        self.child.send("n")
+        self.child.sendline("help")
+
+        # Try completing something with subcommands.
+        self.child.send(":breakpoi\t")
+        self.child.expect_exact(":breakpoint ")
+        self.child.send("\t")
+        self.child.expect_exact("Available completions:")
+        self.child.expect_exact("command")
+        self.child.send("comm\t")
+        self.child.expect_exact(":breakpoint command ")
+        self.child.send("li\t")
+        self.child.expect_exact(":breakpoint command list")
+        self.child.sendline("")
+
+        self.quit()
+
     def setUpCommands(self):
         return [] # REPL doesn't take any setup commands.