Add API for custom LSP requests

Implement a function `ale#lsp_linter#SendRequest` that allows to send
custom LSP requests to an enabled LSP linter.

Resolves #2474

4 files changed, 192 insertions, 4 deletions

diff --git a/autoload/ale/lsp.vim b/autoload/ale/lsp.vim
index 017096cd..1ffdba2e 100644
--- a/autoload/ale/lsp.vim
+++ b/autoload/ale/lsp.vim
@@ -5,6 +5,9 @@
 let s:connections = get(s:, 'connections', {})
 let g:ale_lsp_next_message_id = 1
 
+" A Dictionary to track one-shot callbacks for custom LSP requests
+let s:custom_callbacks = get(s:, 'custom_callbacks', {})
+
 " Given an id, which can be an executable or address, and a project path,
 " create a new connection if needed. Return a unique ID for the connection.
 function! ale#lsp#Register(executable_or_address, project, init_options) abort
@@ -296,10 +299,19 @@ function! ale#lsp#HandleMessage(conn_id, message) abort
     " responses.
     if l:conn.initialized
         for l:response in l:response_list
-            " Call all of the registered handlers with the response.
-            for l:Callback in l:conn.callback_list
-                call ale#util#GetFunction(l:Callback)(a:conn_id, l:response)
-            endfor
+            if has_key(l:response, 'id') && has_key(s:custom_callbacks, l:response.id)
+                " Response to a custom request, call the registered one-shot handler.
+                try
+                    call s:custom_callbacks[l:response.id](l:response)
+                finally
+                    call remove(s:custom_callbacks, l:response.id)
+                endtry
+            else
+                " Call all of the registered handlers with the response.
+                for l:Callback in l:conn.callback_list
+                    call ale#util#GetFunction(l:Callback)(a:conn_id, l:response)
+                endfor
+            endif
         endfor
     endif
 endfunction
@@ -525,6 +537,18 @@ function! ale#lsp#Send(conn_id, message) abort
     return l:id == 0 ? -1 : l:id
 endfunction
 
+" Send a custom request to an LSP server.
+" The given callback is called on response.
+function! ale#lsp#SendCustomRequest(conn_id, message, Callback) abort
+    let l:id = ale#lsp#Send(a:conn_id, a:message)
+
+    if l:id > 0
+        let s:custom_callbacks[l:id] = a:Callback
+    endif
+
+    return l:id
+endfunction
+
 " Notify LSP servers or tsserver if a document is opened, if needed.
 " If a document is opened, 1 will be returned, otherwise 0 will be returned.
 function! ale#lsp#OpenDocument(conn_id, buffer, language_id) abort
diff --git a/autoload/ale/lsp_linter.vim b/autoload/ale/lsp_linter.vim
index 4f439b28..82ae60a2 100644
--- a/autoload/ale/lsp_linter.vim
+++ b/autoload/ale/lsp_linter.vim
@@ -413,3 +413,29 @@ endfunction
 function! ale#lsp_linter#SetLSPLinterMap(replacement_map) abort
     let s:lsp_linter_map = a:replacement_map
 endfunction
+
+" Send a custom request to an LSP linter.
+function! ale#lsp_linter#SendRequest(buffer, linter_name, method, parameters, Callback) abort
+    let l:filetype = ale#linter#ResolveFiletype(getbufvar(a:buffer, '&filetype'))
+    let l:linter_list = ale#linter#GetAll(l:filetype)
+    let l:linter_list = filter(l:linter_list, {_, v -> v.name is# a:linter_name})
+
+    if len(l:linter_list) < 1
+        throw 'Linter "' . a:linter_name . '" not found!'
+    endif
+
+    let l:linter = l:linter_list[0]
+    let l:executable_or_address = ''
+
+    if l:linter.lsp is# 'socket'
+        let l:executable_or_address = ale#linter#GetAddress(a:buffer, l:linter)
+    else
+        let l:executable_or_address = ale#linter#GetExecutable(a:buffer, l:linter)
+    endif
+
+    let l:root = ale#util#GetFunction(l:linter.project_root)(a:buffer)
+    let l:conn_id = l:executable_or_address . ':' . l:root
+    let l:message = [0, a:method, a:parameters]
+
+    return ale#lsp#SendCustomRequest(l:conn_id, l:message, a:Callback) == 0
+endfunction
diff --git a/doc/ale.txt b/doc/ale.txt
index 17f1dde6..8dcbea60 100644
--- a/doc/ale.txt
+++ b/doc/ale.txt
@@ -3191,6 +3191,24 @@ ale#linter#PreventLoading(filetype)               *ale#linter#PreventLoading()*
   |runtimepath| for that filetype. This function can be called from vimrc or
   similar to prevent ALE from loading linters.
 
+
+ale#lsp_linter#SendRequest(buffer, linter_name, method, parameters, Callback)
+                                                 *ale#lsp_linter#SendRequest()*
+
+  Send a custom request to an LSP linter.
+
+  `buffer` must be a valid buffer number, and `linter_name` is a |String|
+  identifying an LSP linter that is available and enabled for the |filetype|
+  of `buffer`. `method` is a |String| identifying an LSP method supported by
+  `linter`, while `parameters` is a |dictionary| of LSP parameters applicable
+  to `method`. `Callback` is a |Funcref| that is called when a response to the
+  request is received, and takes as unique argument a dictionary representing
+  the response to the request obtained from the server.
+
+  The function returns zero if the request is succesfully sent, non-zero
+  otherwise.
+
+
 ale#other_source#ShowResults(buffer, linter_name, loclist)
                                                *ale#other_source#ShowResults()*
 
diff --git a/test/lsp/test_lsp_custom_request.vader b/test/lsp/test_lsp_custom_request.vader
new file mode 100644
index 00000000..e5fecafc
--- /dev/null
+++ b/test/lsp/test_lsp_custom_request.vader
@@ -0,0 +1,120 @@
+Before:
+  runtime autoload/ale/linter.vim
+  runtime autoload/ale/lsp.vim
+  runtime autoload/ale/lsp_linter.vim
+
+  let g:address = 'ccls_address'
+  let g:callback_result = 0
+  let g:conn_id = -1
+  let g:executable = 'ccls'
+  let g:linter_name = 'ccls'
+  let g:magic_number = 42
+  let g:message = -1
+  let g:message_id = 1
+  let g:method = '$ccls/call'
+  let g:parameters = {}
+  let g:project = '/project/root'
+  let g:return_value = -1
+
+  let g:linter_list = [{
+  \   'output_stream': 'stdout',
+  \   'lint_file': 0,
+  \   'language': 'cpp',
+  \   'name': g:linter_name,
+  \   'project_root': {b -> g:project},
+  \   'aliases': [],
+  \   'language_callback': {b -> 'cpp'},
+  \   'read_buffer': 1,
+  \   'command': '%e'
+  \ }]
+
+  " Encode dictionary to jsonrpc
+  function! Encode(obj) abort
+    let l:body = json_encode(a:obj)
+    return 'Content-Length: ' . strlen(l:body) . "\r\n\r\n" . l:body
+  endfunction
+
+  " Register the server with given executable or address
+  function! InitServer(executable_or_address) abort
+    let g:conn_id = ale#lsp#Register(a:executable_or_address, g:project, {})
+    call ale#lsp#HandleMessage(g:conn_id, Encode({'method': 'initialize'}))
+  endfunction
+
+  " Dummy callback
+  function! Callback(response) abort
+    let g:callback_result = a:response.result.value
+  endfunction
+
+  " Replace the GetAll function to mock an LSP linter
+  function! ale#linter#GetAll(filetype) abort
+    return g:linter_list
+  endfunction
+
+  " Replace the Send function to mock an LSP linter
+  function! ale#lsp#Send(conn_id, message) abort
+    let g:message = a:message
+    return g:message_id
+  endfunction
+
+  " Code for a test case
+  function! TestCase() abort
+    " Test sending a custom request
+    let g:return_value = ale#lsp_linter#SendRequest(bufnr('%'), g:linter_name, g:method, g:parameters, function('Callback'))
+
+    AssertEqual
+    \ 0,
+    \ g:return_value
+
+    AssertEqual
+    \ [0, g:method, g:parameters],
+    \ g:message
+
+    " Mock an incoming response to the request
+    call ale#lsp#HandleMessage(g:conn_id, Encode({'id': g:message_id, 'jsonrpc': '2.0', 'result': {'value': g:magic_number}}))
+
+    AssertEqual
+    \ g:magic_number,
+    \ g:callback_result
+  endfunction
+
+After:
+  if g:conn_id isnot v:null
+    call ale#lsp#RemoveConnectionWithID(g:conn_id)
+  endif
+
+  unlet! g:callback_result
+  unlet! g:conn_id
+  unlet! g:executable
+  unlet! g:linter_name
+  unlet! g:magic_number
+  unlet! g:message
+  unlet! g:message_id
+  unlet! g:method
+  unlet! g:parameters
+  unlet! g:project
+  unlet! g:return_value
+
+  delfunction Encode
+  delfunction InitServer
+  delfunction Callback
+  delfunction TestCase
+
+  runtime autoload/ale/linter.vim
+  runtime autoload/ale/lsp.vim
+  runtime autoload/ale/lsp_linter.vim
+
+Given cpp(Empty cpp file):
+Execute(Test custom request to server identified by executable):
+  call InitServer(g:executable)
+  let g:linter_list[0].executable = {b -> g:executable}
+  let g:linter_list[0].lsp = 'stdio'
+
+  call TestCase()
+
+Given cpp(Empty cpp file):
+Execute(Test custom request to server identified by address):
+  call InitServer(g:address)
+  let g:linter_list[0].address = {b -> g:address}
+  let g:linter_list[0].lsp = 'socket'
+
+  call TestCase()