send empty array for setbreakpoints command

[Jaehaks]

1. Problem

Some debugger like matlab-lsp, It removes unused breakpoints when lsp received setbreakpoints command.

Previously, set_breakpoints() function send nothing when there are no breakpoint. It makes that lsp cannot remove remained breakpoints which are set before.

2. Solution

Send setbreakpoints request with empty array even though there is no breakpoints

[mfussenegger]

Can you clarify how you run into this?

If I remove the last breakpoint in a buffer I still get a setBreakpoints command sent like:

{
  arguments = {
    breakpoints = {},
    lines = {},
    source = {
      name = "Foo.java",
      path = "/tmp/Foo.java"
    },
    sourceModified = false
  },
  command = "setBreakpoints",
  seq = 11,
  type = "request"
}

[Jaehaks]

When I executes continue() function these messages are sent from nvimd-dap If I didn't check any breakpoints.

There is no setbreakpoint message between initialize and launch

Content-Length: 343

{"type":"request","arguments":{"linesStartAt1":true,"columnsStartAt1":true,"pathFormat":"path","clientName":"neovim","locale
":"en_US","adapterID":"nvim-dap","clientID":"neovim","supportsStartDebuggingRequest":true,"supportsProgressReporting":true,"
supportsVariableType":true,"supportsRunInTerminalRequest":true},"command":"initialize","seq":1}
Content-Length: 212

{"type":"request","arguments":{"program":"C:\\Users\\USER\\.config\\nvim\\test\\test.m","type":"matlab","cwd":"C:\\Users\\US
ER\\.config\\nvim","request":"launch","name":"MATLAB Debug"},"command":"launch","seq":2}
Content-Length: 56

{"type":"request","command":"configurationDone","seq":3}
Content-Length: 145

{"type":"request","arguments":{"expression":"run('C:\\Users\\USER\\.config\\nvim\\test\\test.m')","context":"repl"},"command
":"evaluate","seq":4}

I created a dap adapter for matlab. To communicate between dap and lsp, I made some read_handler() which send dap message to lsp when the tcp socket received message from dap,
You can find this in nvim-dap-matlab.

When I modify your code like PR, It send empty message correctly.

[mfussenegger]

If I didn't check any breakpoints. There is no setbreakpoint message between initialize and launch

That's sort of expected. setBreakpoints is optional - a client doesn't have to send it if there are no breakpoints.

It makes that lsp cannot remove remained breakpoints which are set before.

If the language server keeps the breakpoints, couldn't you just always remove breakpoints at the end of a debug session?