[lldb] tab completion for `watchpoint set variable`

[MrHate]

Summary

1. Applied the common completion eVariablePathCompletion to command watchpoint set variable;
2. Added a related test case.

[teemperor]

LGTM module minus style nit.

lldb/source/Commands/CommandObjectWatchpoint.cpp

829

I think the != 0 is actually clearer here. Usually if (X) is more for types like Optional or pointers types that can be "nullptrs", but here it's actually checking for the index 0.

[JDevlieghere]

+1 on @teemperor's inline comment but otherwise LGTM

lldb/source/Commands/CommandObjectWatchpoint.cpp

corresponding to the byte size of the data type.");
     // Absorb the '-w' and '-s' options into our option group.
     m_option_group.Append(&m_option_watchpoint, LLDB_OPT_SET_ALL,
                           LLDB_OPT_SET_1);
     m_option_group.Finalize();
   }
 
   ~CommandObjectWatchpointSetVariable() override = default;
 
+  void
+  HandleArgumentCompletion(CompletionRequest &request,
+                           OptionElementVector &opt_element_vector) override {
+    if (request.GetCursorIndex() != 0)
+      return;
+    CommandCompletions::InvokeCommonCompletionCallbacks(
+        GetCommandInterpreter(), CommandCompletions::eVariablePathCompletion,
+        request, nullptr);
+  }
+
   Options *GetOptions() override { return &m_option_group; }
 
 protected:
   static size_t GetVariableCallback(void *baton, const char *name,
                                     VariableList &variable_list) {
     size_t old_size = variable_list.GetSize();
     Target *target = static_cast<Target *>(baton);
     if (target)

lldb/test/API/functionalities/completion/TestCompletion.py

def test_watchpoint_set_ex(self):
         self.complete_from_to(
             'watchpoint set ex',
             'watchpoint set expression ')
 
     def test_watchpoint_set_var(self):
         """Test that 'watchpoint set var' completes to 'watchpoint set variable '."""
         self.complete_from_to('watchpoint set var', 'watchpoint set variable ')
 
+    def test_watchpoint_set_variable_foo(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, '// Break here', lldb.SBFileSpec("main.cpp"))
+        self.complete_from_to('watchpoint set variable fo', 'watchpoint set variable fooo')
+        # Only complete the first argument.
+        self.complete_from_to('watchpoint set variable fooo ', 'watchpoint set variable fooo ')
+
     def test_help_fi(self):
         """Test that 'help fi' completes to ['file', 'finish']."""
         self.complete_from_to(
             'help fi', [
                 'file', 'finish'])
 
     def test_help_watchpoint_s(self):
         """Test that 'help watchpoint s' completes to 'help watchpoint set '."""