Check LSP capabilities before using them

13 files changed, 391 insertions, 233 deletions

diff --git a/autoload/ale/completion.vim b/autoload/ale/completion.vim
index e7da4028..5c054dd7 100644
--- a/autoload/ale/completion.vim
+++ b/autoload/ale/completion.vim
@@ -422,54 +422,60 @@ endfunction
 
 function! s:GetLSPCompletions(linter) abort
     let l:buffer = bufnr('')
-    let l:Callback = a:linter.lsp is# 'tsserver'
-    \   ? function('ale#completion#HandleTSServerResponse')
-    \   : function('ale#completion#HandleLSPResponse')
-
-    let l:lsp_details = ale#lsp_linter#StartLSP(l:buffer, a:linter, l:Callback)
+    let l:lsp_details = ale#lsp_linter#StartLSP(l:buffer, a:linter)
 
     if empty(l:lsp_details)
         return 0
     endif
 
     let l:id = l:lsp_details.connection_id
+    let l:root = l:lsp_details.project_root
+
+    function! OnReady(...) abort closure
+        let l:Callback = a:linter.lsp is# 'tsserver'
+        \   ? function('ale#completion#HandleTSServerResponse')
+        \   : function('ale#completion#HandleLSPResponse')
+        call ale#lsp#RegisterCallback(l:id, l:Callback)
+
+        if a:linter.lsp is# 'tsserver'
+            let l:message = ale#lsp#tsserver_message#Completions(
+            \   l:buffer,
+            \   b:ale_completion_info.line,
+            \   b:ale_completion_info.column,
+            \   b:ale_completion_info.prefix,
+            \)
+        else
+            " Send a message saying the buffer has changed first, otherwise
+            " completions won't know what text is nearby.
+            call ale#lsp#NotifyForChanges(l:id, l:root, l:buffer)
+
+            " For LSP completions, we need to clamp the column to the length of
+            " the line. python-language-server and perhaps others do not implement
+            " this correctly.
+            let l:message = ale#lsp#message#Completion(
+            \   l:buffer,
+            \   b:ale_completion_info.line,
+            \   min([
+            \       b:ale_completion_info.line_length,
+            \       b:ale_completion_info.column,
+            \   ]),
+            \   ale#completion#GetTriggerCharacter(&filetype, b:ale_completion_info.prefix),
+            \)
+        endif
 
-    if a:linter.lsp is# 'tsserver'
-        let l:message = ale#lsp#tsserver_message#Completions(
-        \   l:buffer,
-        \   b:ale_completion_info.line,
-        \   b:ale_completion_info.column,
-        \   b:ale_completion_info.prefix,
-        \)
-    else
-        " Send a message saying the buffer has changed first, otherwise
-        " completions won't know what text is nearby.
-        call ale#lsp#NotifyForChanges(l:lsp_details)
-
-        " For LSP completions, we need to clamp the column to the length of
-        " the line. python-language-server and perhaps others do not implement
-        " this correctly.
-        let l:message = ale#lsp#message#Completion(
-        \   l:buffer,
-        \   b:ale_completion_info.line,
-        \   min([
-        \       b:ale_completion_info.line_length,
-        \       b:ale_completion_info.column,
-        \   ]),
-        \   ale#completion#GetTriggerCharacter(&filetype, b:ale_completion_info.prefix),
-        \)
-    endif
-
-    let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
+        let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
 
-    if l:request_id
-        let b:ale_completion_info.conn_id = l:id
-        let b:ale_completion_info.request_id = l:request_id
+        if l:request_id
+            let b:ale_completion_info.conn_id = l:id
+            let b:ale_completion_info.request_id = l:request_id
 
-        if has_key(a:linter, 'completion_filter')
-            let b:ale_completion_info.completion_filter = a:linter.completion_filter
+            if has_key(a:linter, 'completion_filter')
+                let b:ale_completion_info.completion_filter = a:linter.completion_filter
+            endif
         endif
-    endif
+    endfunction
+
+    call ale#lsp#WaitForCapability(l:id, l:root, 'completion', function('OnReady'))
 endfunction
 
 function! ale#completion#GetCompletions() abort
diff --git a/autoload/ale/definition.vim b/autoload/ale/definition.vim
index 6c70b64c..6c7d7d32 100644
--- a/autoload/ale/definition.vim
+++ b/autoload/ale/definition.vim
@@ -60,43 +60,50 @@ endfunction
 function! s:GoToLSPDefinition(linter, options) abort
     let l:buffer = bufnr('')
     let [l:line, l:column] = getcurpos()[1:2]
+    let l:lsp_details = ale#lsp_linter#StartLSP(l:buffer, a:linter)
 
-    let l:Callback = a:linter.lsp is# 'tsserver'
-    \   ? function('ale#definition#HandleTSServerResponse')
-    \   : function('ale#definition#HandleLSPResponse')
-
-    let l:lsp_details = ale#lsp_linter#StartLSP(l:buffer, a:linter, l:Callback)
+    if a:linter.lsp isnot# 'tsserver'
+        let l:column = min([l:column, len(getline(l:line))])
+    endif
 
     if empty(l:lsp_details)
         return 0
     endif
 
     let l:id = l:lsp_details.connection_id
+    let l:root = l:lsp_details.project_root
+
+    function! OnReady(...) abort closure
+        let l:Callback = a:linter.lsp is# 'tsserver'
+        \   ? function('ale#definition#HandleTSServerResponse')
+        \   : function('ale#definition#HandleLSPResponse')
+        call ale#lsp#RegisterCallback(l:id, l:Callback)
+
+        if a:linter.lsp is# 'tsserver'
+            let l:message = ale#lsp#tsserver_message#Definition(
+            \   l:buffer,
+            \   l:line,
+            \   l:column
+            \)
+        else
+            " Send a message saying the buffer has changed first, or the
+            " definition position probably won't make sense.
+            call ale#lsp#NotifyForChanges(l:id, l:root, l:buffer)
+
+            " For LSP completions, we need to clamp the column to the length of
+            " the line. python-language-server and perhaps others do not implement
+            " this correctly.
+            let l:message = ale#lsp#message#Definition(l:buffer, l:line, l:column)
+        endif
 
-    if a:linter.lsp is# 'tsserver'
-        let l:message = ale#lsp#tsserver_message#Definition(
-        \   l:buffer,
-        \   l:line,
-        \   l:column
-        \)
-    else
-        " Send a message saying the buffer has changed first, or the
-        " definition position probably won't make sense.
-        call ale#lsp#NotifyForChanges(l:lsp_details)
-
-        let l:column = min([l:column, len(getline(l:line))])
-
-        " For LSP completions, we need to clamp the column to the length of
-        " the line. python-language-server and perhaps others do not implement
-        " this correctly.
-        let l:message = ale#lsp#message#Definition(l:buffer, l:line, l:column)
-    endif
+        let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
 
-    let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
+        let s:go_to_definition_map[l:request_id] = {
+        \   'open_in_tab': get(a:options, 'open_in_tab', 0),
+        \}
+    endfunction
 
-    let s:go_to_definition_map[l:request_id] = {
-    \   'open_in_tab': get(a:options, 'open_in_tab', 0),
-    \}
+    call ale#lsp#WaitForCapability(l:id, l:root, 'definition', function('OnReady'))
 endfunction
 
 function! ale#definition#GoTo(options) abort
diff --git a/autoload/ale/hover.vim b/autoload/ale/hover.vim
index 6d131adc..5e97e16e 100644
--- a/autoload/ale/hover.vim
+++ b/autoload/ale/hover.vim
@@ -93,45 +93,51 @@ function! ale#hover#HandleLSPResponse(conn_id, response) abort
 endfunction
 
 function! s:ShowDetails(linter, buffer, line, column, opt) abort
-    let l:Callback = a:linter.lsp is# 'tsserver'
-    \   ? function('ale#hover#HandleTSServerResponse')
-    \   : function('ale#hover#HandleLSPResponse')
-
-    let l:lsp_details = ale#lsp_linter#StartLSP(a:buffer, a:linter, l:Callback)
+    let l:lsp_details = ale#lsp_linter#StartLSP(a:buffer, a:linter)
 
     if empty(l:lsp_details)
         return 0
     endif
 
     let l:id = l:lsp_details.connection_id
+    let l:root = l:lsp_details.project_root
     let l:language_id = l:lsp_details.language_id
 
-    if a:linter.lsp is# 'tsserver'
-        let l:column = a:column
+    function! OnReady(...) abort closure
+        let l:Callback = a:linter.lsp is# 'tsserver'
+        \   ? function('ale#hover#HandleTSServerResponse')
+        \   : function('ale#hover#HandleLSPResponse')
+        call ale#lsp#RegisterCallback(l:id, l:Callback)
 
-        let l:message = ale#lsp#tsserver_message#Quickinfo(
-        \   a:buffer,
-        \   a:line,
-        \   l:column
-        \)
-    else
-        " Send a message saying the buffer has changed first, or the
-        " hover position probably won't make sense.
-        call ale#lsp#NotifyForChanges(l:lsp_details)
+        if a:linter.lsp is# 'tsserver'
+            let l:column = a:column
 
-        let l:column = min([a:column, len(getbufline(a:buffer, a:line)[0])])
+            let l:message = ale#lsp#tsserver_message#Quickinfo(
+            \   a:buffer,
+            \   a:line,
+            \   l:column
+            \)
+        else
+            " Send a message saying the buffer has changed first, or the
+            " hover position probably won't make sense.
+            call ale#lsp#NotifyForChanges(l:id, l:root, a:buffer)
 
-        let l:message = ale#lsp#message#Hover(a:buffer, a:line, l:column)
-    endif
+            let l:column = min([a:column, len(getbufline(a:buffer, a:line)[0])])
+
+            let l:message = ale#lsp#message#Hover(a:buffer, a:line, l:column)
+        endif
+
+        let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
 
-    let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
+        let s:hover_map[l:request_id] = {
+        \   'buffer': a:buffer,
+        \   'line': a:line,
+        \   'column': l:column,
+        \   'hover_from_balloonexpr': get(a:opt, 'called_from_balloonexpr', 0),
+        \}
+    endfunction
 
-    let s:hover_map[l:request_id] = {
-    \   'buffer': a:buffer,
-    \   'line': a:line,
-    \   'column': l:column,
-    \   'hover_from_balloonexpr': get(a:opt, 'called_from_balloonexpr', 0),
-    \}
+    call ale#lsp#WaitForCapability(l:id, l:root, 'hover', function('OnReady'))
 endfunction
 
 " Obtain Hover information for the specified position
diff --git a/autoload/ale/lsp.vim b/autoload/ale/lsp.vim
index 1dac3ab1..312319ab 100644
--- a/autoload/ale/lsp.vim
+++ b/autoload/ale/lsp.vim
@@ -18,6 +18,7 @@ function! ale#lsp#NewConnection(initialization_options) abort
     " initialization_options: Options to send to the server.
     " capabilities: Features the server supports.
     let l:conn = {
+    \   'is_tsserver': 0,
     \   'id': '',
     \   'data': '',
     \   'projects': {},
@@ -188,6 +189,16 @@ function! s:MarkProjectAsInitialized(conn, project) abort
 
     " Remove the messages now.
     let a:conn.message_queue = []
+
+    " Call capabilities callbacks queued for the project.
+    for [l:capability, l:Callback] in a:project.capabilities_queue
+        if a:conn.is_tsserver || a:conn.capabilities[l:capability]
+            call call(l:Callback, [a:conn.id, a:project.root])
+        endif
+    endfor
+
+    " Clear the queued callbacks now.
+    let a:project.capabilities_queue = []
 endfunction
 
 function! s:HandleInitializeResponse(conn, response) abort
@@ -302,22 +313,43 @@ function! s:HandleCommandMessage(job_id, message) abort
     call ale#lsp#HandleMessage(l:conn, a:message)
 endfunction
 
-function! ale#lsp#RegisterProject(conn, project_root) abort
+" Given a connection ID, mark it as a tsserver connection, so it will be
+" handled that way.
+function! ale#lsp#MarkConnectionAsTsserver(conn_id) abort
+    let l:conn = s:FindConnection('id', a:conn_id)
+
+    if !empty(l:conn)
+        let l:conn.is_tsserver = 1
+    endif
+endfunction
+
+" Register a project for an LSP connection.
+"
+" This function will throw if the connection doesn't exist.
+function! ale#lsp#RegisterProject(conn_id, project_root) abort
+    let l:conn = s:FindConnection('id', a:conn_id)
+
     " Empty strings can't be used for Dictionary keys in NeoVim, due to E713.
     " This appears to be a nonsensical bug in NeoVim.
     let l:key = empty(a:project_root) ? '<<EMPTY>>' : a:project_root
 
-    if !has_key(a:conn.projects, l:key)
+    if !has_key(l:conn.projects, l:key)
         " Tools without project roots are ready right away, like tsserver.
-        let a:conn.projects[l:key] = {
+        let l:conn.projects[l:key] = {
+        \   'root': a:project_root,
         \   'initialized': empty(a:project_root),
         \   'init_request_id': 0,
         \   'message_queue': [],
+        \   'capabilities_queue': [],
         \}
     endif
 endfunction
 
 function! ale#lsp#GetProject(conn, project_root) abort
+    if empty(a:conn)
+        return {}
+    endif
+
     let l:key = empty(a:project_root) ? '<<EMPTY>>' : a:project_root
 
     return get(a:conn.projects, l:key, {})
@@ -327,7 +359,7 @@ endfunction
 "
 " The job ID will be returned for for the program if it ran, otherwise
 " 0 will be returned.
-function! ale#lsp#StartProgram(executable, command, project_root, callback, initialization_options) abort
+function! ale#lsp#StartProgram(executable, command, init_options) abort
     if !executable(a:executable)
         return 0
     endif
@@ -335,7 +367,7 @@ function! ale#lsp#StartProgram(executable, command, project_root, callback, init
     let l:conn = s:FindConnection('executable', a:executable)
 
     " Get the current connection or a new one.
-    let l:conn = !empty(l:conn) ? l:conn : ale#lsp#NewConnection(a:initialization_options)
+    let l:conn = !empty(l:conn) ? l:conn : ale#lsp#NewConnection(a:init_options)
     let l:conn.executable = a:executable
 
     if !has_key(l:conn, 'id') || !ale#job#IsRunning(l:conn.id)
@@ -353,18 +385,15 @@ function! ale#lsp#StartProgram(executable, command, project_root, callback, init
     endif
 
     let l:conn.id = l:job_id
-    " Add the callback to the List if it's not there already.
-    call uniq(sort(add(l:conn.callback_list, a:callback)))
-    call ale#lsp#RegisterProject(l:conn, a:project_root)
 
     return l:job_id
 endfunction
 
 " Connect to an address and set up a callback for handling responses.
-function! ale#lsp#ConnectToAddress(address, project_root, callback, initialization_options) abort
+function! ale#lsp#ConnectToAddress(address, init_options) abort
     let l:conn = s:FindConnection('id', a:address)
     " Get the current connection or a new one.
-    let l:conn = !empty(l:conn) ? l:conn : ale#lsp#NewConnection(a:initialization_options)
+    let l:conn = !empty(l:conn) ? l:conn : ale#lsp#NewConnection(a:init_options)
 
     if !has_key(l:conn, 'channel_id') || !ale#socket#IsOpen(l:conn.channel_id)
         let l:conn.channel_id = ale#socket#Open(a:address, {
@@ -377,13 +406,21 @@ function! ale#lsp#ConnectToAddress(address, project_root, callback, initializati
     endif
 
     let l:conn.id = a:address
-    " Add the callback to the List if it's not there already.
-    call uniq(sort(add(l:conn.callback_list, a:callback)))
-    call ale#lsp#RegisterProject(l:conn, a:project_root)
 
     return a:address
 endfunction
 
+" Given a connection ID and a callback, register that callback for handling
+" messages if the connection exists.
+function! ale#lsp#RegisterCallback(conn_id, callback) abort
+    let l:conn = s:FindConnection('id', a:conn_id)
+
+    if !empty(l:conn)
+        " Add the callback to the List if it's not there already.
+        call uniq(sort(add(l:conn.callback_list, a:callback)))
+    endif
+endfunction
+
 " Stop all LSP connections, closing all jobs and channels, and removing any
 " queued messages.
 function! ale#lsp#StopAll() abort
@@ -421,11 +458,6 @@ function! ale#lsp#Send(conn_id, message, ...) abort
     let l:project_root = get(a:000, 0, '')
 
     let l:conn = s:FindConnection('id', a:conn_id)
-
-    if empty(l:conn)
-        return 0
-    endif
-
     let l:project = ale#lsp#GetProject(l:conn, l:project_root)
 
     if empty(l:project)
@@ -459,45 +491,22 @@ function! ale#lsp#Send(conn_id, message, ...) abort
     return l:id == 0 ? -1 : l:id
 endfunction
 
-" The Document details Dictionary should contain the following keys.
-"
-"  buffer - The buffer number for the document.
-"  connection_id - The connection ID for the LSP server.
-"  command - The command to run to start the LSP connection.
-"  project_root - The project root for the LSP project.
-"  language_id - The language ID for the project, like 'python', 'rust', etc.
-
-" Create a new Dictionary containing more connection details, with the
-" following information added:
-"
-"   conn - An existing LSP connection for the document.
-"   document_open - 1 if the document is currently open, 0 otherwise.
-function! s:ExtendDocumentDetails(details) abort
-    let l:extended = copy(a:details)
-    let l:conn = s:FindConnection('id', a:details.connection_id)
-
-    let l:extended.conn = l:conn
-    let l:extended.document_open = !empty(l:conn)
-    \   && has_key(l:conn.open_documents, a:details.buffer)
-
-    return l:extended
-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(basic_details) abort
-    let l:d = s:ExtendDocumentDetails(a:basic_details)
+function! ale#lsp#OpenDocument(conn_id, project_root, buffer, language_id) abort
+    let l:conn = s:FindConnection('id', a:conn_id)
     let l:opened = 0
 
-    if !empty(l:d.conn) && !l:d.document_open
-        if empty(l:d.language_id)
-            let l:message = ale#lsp#tsserver_message#Open(l:d.buffer)
+    " FIXME: Return 1 if the document is already open?
+    if !empty(l:conn) && !has_key(l:conn.open_documents, a:buffer)
+        if l:conn.is_tsserver
+            let l:message = ale#lsp#tsserver_message#Open(a:buffer)
         else
-            let l:message = ale#lsp#message#DidOpen(l:d.buffer, l:d.language_id)
+            let l:message = ale#lsp#message#DidOpen(a:buffer, a:language_id)
         endif
 
-        call ale#lsp#Send(l:d.connection_id, l:message, l:d.project_root)
-        let l:d.conn.open_documents[l:d.buffer] = getbufvar(l:d.buffer, 'changedtick')
+        call ale#lsp#Send(a:conn_id, l:message, a:project_root)
+        let l:conn.open_documents[a:buffer] = getbufvar(a:buffer, 'changedtick')
         let l:opened = 1
     endif
 
@@ -506,25 +515,50 @@ endfunction
 
 " Notify LSP servers or tsserver that a document has changed, if needed.
 " If a notification is sent, 1 will be returned, otherwise 0 will be returned.
-function! ale#lsp#NotifyForChanges(basic_details) abort
-    let l:d = s:ExtendDocumentDetails(a:basic_details)
+function! ale#lsp#NotifyForChanges(conn_id, project_root, buffer) abort
+    let l:conn = s:FindConnection('id', a:conn_id)
     let l:notified = 0
 
-    if l:d.document_open
-        let l:new_tick = getbufvar(l:d.buffer, 'changedtick')
+    if !empty(l:conn) && has_key(l:conn.open_documents, a:buffer)
+        let l:new_tick = getbufvar(a:buffer, 'changedtick')
 
-        if l:d.conn.open_documents[l:d.buffer] < l:new_tick
-            if empty(l:d.language_id)
-                let l:message = ale#lsp#tsserver_message#Change(l:d.buffer)
+        if l:conn.open_documents[a:buffer] < l:new_tick
+            if l:conn.is_tsserver
+                let l:message = ale#lsp#tsserver_message#Change(a:buffer)
             else
-                let l:message = ale#lsp#message#DidChange(l:d.buffer)
+                let l:message = ale#lsp#message#DidChange(a:buffer)
             endif
 
-            call ale#lsp#Send(l:d.connection_id, l:message, l:d.project_root)
-            let l:d.conn.open_documents[l:d.buffer] = l:new_tick
+            call ale#lsp#Send(a:conn_id, l:message, a:project_root)
+            let l:conn.open_documents[a:buffer] = l:new_tick
             let l:notified = 1
         endif
     endif
 
     return l:notified
 endfunction
+
+" Given some LSP details that must contain at least `connection_id` and
+" `project_root` keys,
+function! ale#lsp#WaitForCapability(conn_id, project_root, capability, callback) abort
+    let l:conn = s:FindConnection('id', a:conn_id)
+    let l:project = ale#lsp#GetProject(l:conn, a:project_root)
+
+    if empty(l:project)
+        return 0
+    endif
+
+    if type(get(l:conn.capabilities, a:capability, v:null)) isnot type(0)
+        throw 'Invalid capability ' . a:capability
+    endif
+
+    if l:project.initialized
+        if l:conn.is_tsserver || l:conn.capabilities[a:capability]
+            " The project has been initialized, so call the callback now.
+            call call(a:callback, [a:conn_id, a:project_root])
+        endif
+    else
+        " Call the callback later, once we have the information we need.
+        call add(l:project.capabilities_queue, [a:capability, a:callback])
+    endif
+endfunction
diff --git a/autoload/ale/lsp_linter.vim b/autoload/ale/lsp_linter.vim
index 6dc78e4c..87aee759 100644
--- a/autoload/ale/lsp_linter.vim
+++ b/autoload/ale/lsp_linter.vim
@@ -126,10 +126,9 @@ function! ale#lsp_linter#GetOptions(buffer, linter) abort
     return l:initialization_options
 endfunction
 
-" Given a buffer, an LSP linter, and a callback to register for handling
-" messages, start up an LSP linter and get ready to receive errors or
-" completions.
-function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
+" Given a buffer, an LSP linter, start up an LSP linter and get ready to
+" receive messages for the document.
+function! ale#lsp_linter#StartLSP(buffer, linter) abort
     let l:command = ''
     let l:address = ''
     let l:root = ale#util#GetFunction(a:linter.project_root_callback)(a:buffer)
@@ -140,16 +139,11 @@ function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
         return {}
     endif
 
-    let l:initialization_options = ale#lsp_linter#GetOptions(a:buffer, a:linter)
+    let l:init_options = ale#lsp_linter#GetOptions(a:buffer, a:linter)
 
     if a:linter.lsp is# 'socket'
         let l:address = ale#linter#GetAddress(a:buffer, a:linter)
-        let l:conn_id = ale#lsp#ConnectToAddress(
-        \   l:address,
-        \   l:root,
-        \   a:callback,
-        \   l:initialization_options,
-        \)
+        let l:conn_id = ale#lsp#ConnectToAddress(l:address, l:init_options)
     else
         let l:executable = ale#linter#GetExecutable(a:buffer, a:linter)
 
@@ -164,14 +158,10 @@ function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
         let l:conn_id = ale#lsp#StartProgram(
         \   l:executable,
         \   l:command,
-        \   l:root,
-        \   a:callback,
-        \   l:initialization_options,
+        \   l:init_options,
         \)
     endif
 
-    let l:language_id = ale#util#GetFunction(a:linter.language_callback)(a:buffer)
-
     if empty(l:conn_id)
         if g:ale_history_enabled && !empty(l:command)
             call ale#history#Add(a:buffer, 'failed', l:conn_id, l:command)
@@ -180,6 +170,16 @@ function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
         return {}
     endif
 
+    " tsserver behaves differently, so tell the LSP API that it is tsserver.
+    if a:linter.lsp is# 'tsserver'
+        call ale#lsp#MarkConnectionAsTsserver(l:conn_id)
+    endif
+
+    " Register the project now the connection is ready.
+    call ale#lsp#RegisterProject(l:conn_id, l:root)
+
+    let l:language_id = ale#util#GetFunction(a:linter.language_callback)(a:buffer)
+
     let l:details = {
     \   'buffer': a:buffer,
     \   'connection_id': l:conn_id,
@@ -188,7 +188,7 @@ function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
     \   'language_id': l:language_id,
     \}
 
-    if ale#lsp#OpenDocument(l:details)
+    if ale#lsp#OpenDocument(l:conn_id, l:root, a:buffer, l:language_id)
         if g:ale_history_enabled && !empty(l:command)
             call ale#history#Add(a:buffer, 'started', l:conn_id, l:command)
         endif
@@ -196,7 +196,7 @@ function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
 
     " The change message needs to be sent for tsserver before doing anything.
     if a:linter.lsp is# 'tsserver'
-        call ale#lsp#NotifyForChanges(l:details)
+        call ale#lsp#NotifyForChanges(l:conn_id, l:root, a:buffer)
     endif
 
     return l:details
@@ -204,11 +204,7 @@ endfunction
 
 function! ale#lsp_linter#CheckWithLSP(buffer, linter) abort
     let l:info = g:ale_buffer_info[a:buffer]
-    let l:lsp_details = ale#lsp_linter#StartLSP(
-    \   a:buffer,
-    \   a:linter,
-    \   function('ale#lsp_linter#HandleLSPResponse'),
-    \)
+    let l:lsp_details = ale#lsp_linter#StartLSP(a:buffer, a:linter)
 
     if empty(l:lsp_details)
         return 0
@@ -217,25 +213,25 @@ function! ale#lsp_linter#CheckWithLSP(buffer, linter) abort
     let l:id = l:lsp_details.connection_id
     let l:root = l:lsp_details.project_root
 
+    " Register a callback now for handling errors now.
+    let l:Callback = function('ale#lsp_linter#HandleLSPResponse')
+    call ale#lsp#RegisterCallback(l:id, l:Callback)
+
     " Remember the linter this connection is for.
     let s:lsp_linter_map[l:id] = a:linter.name
 
     if a:linter.lsp is# 'tsserver'
         let l:message = ale#lsp#tsserver_message#Geterr(a:buffer)
-        let l:request_id = ale#lsp#Send(l:id, l:message, l:root)
-
-        let l:notified = l:request_id != 0
+        let l:notified = ale#lsp#Send(l:id, l:message, l:root) != 0
     else
-        let l:notified = ale#lsp#NotifyForChanges(l:lsp_details)
+        let l:notified = ale#lsp#NotifyForChanges(l:id, l:root, a:buffer)
     endif
 
     " If this was a file save event, also notify the server of that.
     if a:linter.lsp isnot# 'tsserver'
     \&& getbufvar(a:buffer, 'ale_save_event_fired', 0)
         let l:save_message = ale#lsp#message#DidSave(a:buffer)
-        let l:request_id = ale#lsp#Send(l:id, l:save_message, l:root)
-
-        let l:notified = l:request_id != 0
+        let l:notified = ale#lsp#Send(l:id, l:save_message, l:root) != 0
     endif
 
     if l:notified
diff --git a/autoload/ale/references.vim b/autoload/ale/references.vim
index 89df69eb..3a710b7b 100644
--- a/autoload/ale/references.vim
+++ b/autoload/ale/references.vim
@@ -68,37 +68,46 @@ function! s:FindReferences(linter) abort
     let l:buffer = bufnr('')
     let [l:line, l:column] = getcurpos()[1:2]
 
-    let l:Callback = a:linter.lsp is# 'tsserver'
-    \   ? function('ale#references#HandleTSServerResponse')
-    \   : function('ale#references#HandleLSPResponse')
+    if a:linter.lsp isnot# 'tsserver'
+        let l:column = min([l:column, len(getline(l:line))])
+    endif
 
-    let l:lsp_details = ale#lsp_linter#StartLSP(l:buffer, a:linter, l:Callback)
+    let l:lsp_details = ale#lsp_linter#StartLSP(l:buffer, a:linter)
 
     if empty(l:lsp_details)
         return 0
     endif
 
     let l:id = l:lsp_details.connection_id
+    let l:root = l:lsp_details.project_root
 
-    if a:linter.lsp is# 'tsserver'
-        let l:message = ale#lsp#tsserver_message#References(
-        \   l:buffer,
-        \   l:line,
-        \   l:column
-        \)
-    else
-        " Send a message saying the buffer has changed first, or the
-        " references position probably won't make sense.
-        call ale#lsp#NotifyForChanges(l:lsp_details)
+    function! OnReady(...) abort closure
+        let l:Callback = a:linter.lsp is# 'tsserver'
+        \   ? function('ale#references#HandleTSServerResponse')
+        \   : function('ale#references#HandleLSPResponse')
 
-        let l:column = min([l:column, len(getline(l:line))])
+        call ale#lsp#RegisterCallback(l:id, l:Callback)
 
-        let l:message = ale#lsp#message#References(l:buffer, l:line, l:column)
-    endif
+        if a:linter.lsp is# 'tsserver'
+            let l:message = ale#lsp#tsserver_message#References(
+            \   l:buffer,
+            \   l:line,
+            \   l:column
+            \)
+        else
+            " Send a message saying the buffer has changed first, or the
+            " references position probably won't make sense.
+            call ale#lsp#NotifyForChanges(l:id, l:root, l:buffer)
+
+            let l:message = ale#lsp#message#References(l:buffer, l:line, l:column)
+        endif
+
+        let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
 
-    let l:request_id = ale#lsp#Send(l:id, l:message, l:lsp_details.project_root)
+        let s:references_map[l:request_id] = {}
+    endfunction
 
-    let s:references_map[l:request_id] = {}
+    call ale#lsp#WaitForCapability(l:id, l:root, 'references', function('OnReady'))
 endfunction
 
 function! ale#references#Find() abort
diff --git a/test/completion/test_lsp_completion_messages.vader b/test/completion/test_lsp_completion_messages.vader
index 00a174dc..30a9c8e1 100644
--- a/test/completion/test_lsp_completion_messages.vader
+++ b/test/completion/test_lsp_completion_messages.vader
@@ -13,11 +13,11 @@ Before:
   runtime autoload/ale/lsp.vim
 
   let g:message_list = []
+  let g:capability_checked = ''
   let g:Callback = ''
+  let g:WaitCallback = v:null
 
-  function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
-    let g:Callback = a:callback
-
+  function! ale#lsp_linter#StartLSP(buffer, linter) abort
     let l:conn = ale#lsp#NewConnection({})
     let l:conn.id = 347
     let l:conn.open_documents = {a:buffer : -1}
@@ -35,6 +35,15 @@ Before:
     return 'i'
   endfunction
 
+  function! ale#lsp#WaitForCapability(conn_id, project_root, capability, callback) abort
+    let g:capability_checked = a:capability
+    let g:WaitCallback = a:callback
+  endfunction
+
+  function! ale#lsp#RegisterCallback(conn_id, callback) abort
+    let g:Callback = a:callback
+  endfunction
+
   " Replace the Send function for LSP, so we can monitor calls to it.
   function! ale#lsp#Send(conn_id, message, ...) abort
     call add(g:message_list, a:message)
@@ -44,6 +53,8 @@ After:
   Restore
 
   unlet! g:message_list
+  unlet! g:capability_checked
+  unlet! g:WaitCallback
   unlet! g:Callback
   unlet! b:ale_old_omnifunc
   unlet! b:ale_old_completopt
@@ -84,6 +95,13 @@ Execute(The right message should be sent for the initial tsserver request):
 
   call ale#completion#GetCompletions()
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'completion', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   " We should send the right callback.
   AssertEqual
   \ 'function(''ale#completion#HandleTSServerResponse'')',
@@ -164,6 +182,13 @@ Execute(The right message should be sent for the initial LSP request):
 
   call ale#completion#GetCompletions()
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'completion', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   " We should send the right callback.
   AssertEqual
   \ 'function(''ale#completion#HandleLSPResponse'')',
diff --git a/test/lsp/test_did_save_event.vader b/test/lsp/test_did_save_event.vader
index b696ee4b..428135fb 100644
--- a/test/lsp/test_did_save_event.vader
+++ b/test/lsp/test_did_save_event.vader
@@ -14,7 +14,6 @@ Before:
   let g:ale_lsp_next_message_id = 1
   let g:ale_run_synchronously = 1
   let g:message_list = []
-  let g:Callback = ''
 
   function! LanguageCallback() abort
     return 'foobar'
@@ -34,9 +33,7 @@ Before:
   \ })
   let g:ale_linters = {'foobar': ['dummy_linter']}
 
-  function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
-    let g:Callback = a:callback
-
+  function! ale#lsp_linter#StartLSP(buffer, linter) abort
     let l:conn = ale#lsp#NewConnection({})
     let l:conn.id = 347
     let l:conn.open_documents = {a:buffer : -1}
@@ -59,7 +56,6 @@ After:
 
   unlet! b:ale_enabled
   unlet! b:ale_linters
-  unlet! g:Callback
   unlet! g:message_list
 
   delfunction LanguageCallback
diff --git a/test/lsp/test_lsp_command_formatting.vader b/test/lsp/test_lsp_command_formatting.vader
index f436397f..9d2c84ee 100644
--- a/test/lsp/test_lsp_command_formatting.vader
+++ b/test/lsp/test_lsp_command_formatting.vader
@@ -23,15 +23,14 @@ Execute(Command formatting should be applied correctly for LSP linters):
   \   'executable': has('win32') ? 'cmd': 'true',
   \   'command': '%e --foo',
   \ },
-  \ {->0}
   \)
 
   if has('win32')
     AssertEqual
-    \ ['cmd', 'cmd /s/c "cmd --foo"', '/foo/bar'],
-    \ g:args[:2]
+    \ ['cmd', 'cmd /s/c "cmd --foo"', {}],
+    \ g:args
   else
     AssertEqual
-    \ ['true', [&shell, '-c', '''true'' --foo'], '/foo/bar'],
-    \ g:args[:2]
+    \ ['true', [&shell, '-c', '''true'' --foo'], {}],
+    \ g:args
   endif
diff --git a/test/lsp/test_lsp_connections.vader b/test/lsp/test_lsp_connections.vader
index 8651d801..ae64eadb 100644
--- a/test/lsp/test_lsp_connections.vader
+++ b/test/lsp/test_lsp_connections.vader
@@ -2,6 +2,10 @@ Before:
   let g:ale_lsp_next_message_id = 1
 
 After:
+  if exists('b:conn') && has_key(b:conn, 'id')
+    call ale#lsp#RemoveConnectionWithID(b:conn.id)
+  endif
+
   unlet! b:data
   unlet! b:conn
 
@@ -223,17 +227,20 @@ Execute(ale#lsp#ReadMessageData() should handle a message with part of a second
   \ )
 
 Execute(Projects with regular project roots should be registered correctly):
-  let b:conn = {'projects': {}}
-
-  call ale#lsp#RegisterProject(b:conn, '/foo/bar')
+  let b:conn = ale#lsp#NewConnection({})
+  call ale#lsp#RegisterProject(b:conn.id, '/foo/bar')
 
   AssertEqual
   \ {
-  \   'projects': {
-  \     '/foo/bar': {'initialized': 0, 'message_queue': [], 'init_request_id': 0},
+  \   '/foo/bar': {
+  \     'root': '/foo/bar',
+  \     'initialized': 0,
+  \     'message_queue': [],
+  \     'capabilities_queue': [],
+  \     'init_request_id': 0,
   \   },
   \ },
-  \ b:conn
+  \ b:conn.projects
 
 Execute(Projects with regular project roots should be fetched correctly):
   let b:conn = {
@@ -247,17 +254,20 @@ Execute(Projects with regular project roots should be fetched correctly):
   \ ale#lsp#GetProject(b:conn, '/foo/bar')
 
 Execute(Projects with empty project roots should be registered correctly):
-  let b:conn = {'projects': {}}
-
-  call ale#lsp#RegisterProject(b:conn, '')
+  let b:conn = ale#lsp#NewConnection({})
+  call ale#lsp#RegisterProject(b:conn.id, '')
 
   AssertEqual
   \ {
-  \   'projects': {
-  \     '<<EMPTY>>': {'initialized': 1, 'message_queue': [], 'init_request_id': 0},
+  \   '<<EMPTY>>': {
+  \     'root': '',
+  \     'initialized': 1,
+  \     'message_queue': [],
+  \     'capabilities_queue': [],
+  \     'init_request_id': 0,
   \   },
   \ },
-  \ b:conn
+  \ b:conn.projects
 
 Execute(Projects with empty project roots should be fetched correctly):
   let b:conn = {
diff --git a/test/lsp/test_other_initialize_message_handling.vader b/test/lsp/test_other_initialize_message_handling.vader
index f9567ee0..45457979 100644
--- a/test/lsp/test_other_initialize_message_handling.vader
+++ b/test/lsp/test_other_initialize_message_handling.vader
@@ -3,6 +3,7 @@ Before:
   \ 'initialized': 0,
   \ 'init_request_id': 3,
   \ 'message_queue': [],
+  \ 'capabilities_queue': [],
   \}
 
   let b:conn = {
@@ -34,6 +35,7 @@ Execute(publishDiagnostics messages with files inside project directories should
   \   'initialized': 0,
   \   'init_request_id': 3,
   \   'message_queue': [],
+  \   'capabilities_queue': [],
   \ },
   \ b:project
 
@@ -47,6 +49,7 @@ Execute(publishDiagnostics messages with files inside project directories should
   \   'initialized': 1,
   \   'init_request_id': 3,
   \   'message_queue': [],
+  \   'capabilities_queue': [],
   \ },
   \ b:project
 
@@ -60,6 +63,7 @@ Execute(Messages with no method and capabilities should initialize projects):
   \   'initialized': 1,
   \   'init_request_id': 3,
   \   'message_queue': [],
+  \   'capabilities_queue': [],
   \ },
   \ b:project
 
@@ -120,6 +124,7 @@ Execute(Capabilities should bet set up correctly):
   \     '/foo/bar': {
   \       'initialized': 1,
   \       'message_queue': [],
+  \       'capabilities_queue': [],
   \       'init_request_id': 3,
   \     },
   \   },
@@ -170,6 +175,7 @@ Execute(Disabled capabilities should be recognised correctly):
   \     '/foo/bar': {
   \       'initialized': 1,
   \       'message_queue': [],
+  \       'capabilities_queue': [],
   \       'init_request_id': 3,
   \     },
   \   },
diff --git a/test/test_find_references.vader b/test/test_find_references.vader
index 150e0471..ecced068 100644
--- a/test/test_find_references.vader
+++ b/test/test_find_references.vader
@@ -3,20 +3,20 @@ Before:
   call ale#test#SetFilename('dummy.txt')
 
   let g:old_filename = expand('%:p')
-  let g:Callback = 0
+  let g:Callback = ''
   let g:expr_list = []
   let g:message_list = []
   let g:preview_called = 0
   let g:item_list = []
+  let g:capability_checked = ''
+  let g:WaitCallback = v:null
 
   runtime autoload/ale/linter.vim
   runtime autoload/ale/lsp.vim
   runtime autoload/ale/util.vim
   runtime autoload/ale/preview.vim
 
-  function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
-    let g:Callback = a:callback
-
+  function! ale#lsp_linter#StartLSP(buffer, linter) abort
     let l:conn = ale#lsp#NewConnection({})
     let l:conn.id = 347
     let l:conn.open_documents = {a:buffer : -1}
@@ -29,6 +29,15 @@ Before:
     \}
   endfunction
 
+  function! ale#lsp#WaitForCapability(conn_id, project_root, capability, callback) abort
+    let g:capability_checked = a:capability
+    let g:WaitCallback = a:callback
+  endfunction
+
+  function! ale#lsp#RegisterCallback(conn_id, callback) abort
+    let g:Callback = a:callback
+  endfunction
+
   function! ale#lsp#Send(conn_id, message, root) abort
     call add(g:message_list, a:message)
 
@@ -50,6 +59,8 @@ After:
   call ale#test#RestoreDirectory()
   call ale#linter#Reset()
 
+  unlet! g:capability_checked
+  unlet! g:WaitCallback
   unlet! g:old_filename
   unlet! g:Callback
   unlet! g:message_list
@@ -152,6 +163,13 @@ Execute(tsserver reference requests should be sent):
 
   ALEFindReferences
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'references', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   AssertEqual
   \ 'function(''ale#references#HandleTSServerResponse'')',
   \ string(g:Callback)
@@ -226,6 +244,13 @@ Execute(LSP reference requests should be sent):
 
   ALEFindReferences
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'references', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   AssertEqual
   \ 'function(''ale#references#HandleLSPResponse'')',
   \ string(g:Callback)
diff --git a/test/test_go_to_definition.vader b/test/test_go_to_definition.vader
index 749f4d7e..7f0e3fcb 100644
--- a/test/test_go_to_definition.vader
+++ b/test/test_go_to_definition.vader
@@ -3,17 +3,17 @@ Before:
   call ale#test#SetFilename('dummy.txt')
 
   let g:old_filename = expand('%:p')
-  let g:Callback = 0
+  let g:Callback = ''
   let g:message_list = []
   let g:expr_list = []
+  let g:capability_checked = ''
+  let g:WaitCallback = v:null
 
   runtime autoload/ale/linter.vim
   runtime autoload/ale/lsp.vim
   runtime autoload/ale/util.vim
 
-  function! ale#lsp_linter#StartLSP(buffer, linter, callback) abort
-    let g:Callback = a:callback
-
+  function! ale#lsp_linter#StartLSP(buffer, linter) abort
     let l:conn = ale#lsp#NewConnection({})
     let l:conn.id = 347
     let l:conn.open_documents = {a:buffer : -1}
@@ -26,6 +26,15 @@ Before:
     \}
   endfunction
 
+  function! ale#lsp#WaitForCapability(conn_id, project_root, capability, callback) abort
+    let g:capability_checked = a:capability
+    let g:WaitCallback = a:callback
+  endfunction
+
+  function! ale#lsp#RegisterCallback(conn_id, callback) abort
+    let g:Callback = a:callback
+  endfunction
+
   function! ale#lsp#Send(conn_id, message, root) abort
     call add(g:message_list, a:message)
 
@@ -42,6 +51,8 @@ After:
   call ale#test#RestoreDirectory()
   call ale#linter#Reset()
 
+  unlet! g:capability_checked
+  unlet! g:WaitCallback
   unlet! g:old_filename
   unlet! g:Callback
   unlet! g:message_list
@@ -137,6 +148,13 @@ Execute(tsserver completion requests should be sent):
 
   ALEGoToDefinition
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'definition', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   AssertEqual
   \ 'function(''ale#definition#HandleTSServerResponse'')',
   \ string(g:Callback)
@@ -151,6 +169,13 @@ Execute(tsserver tab completion requests should be sent):
 
   ALEGoToDefinitionInTab
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'definition', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   AssertEqual
   \ 'function(''ale#definition#HandleTSServerResponse'')',
   \ string(g:Callback)
@@ -276,6 +301,13 @@ Execute(LSP completion requests should be sent):
 
   ALEGoToDefinition
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'definition', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   AssertEqual
   \ 'function(''ale#definition#HandleLSPResponse'')',
   \ string(g:Callback)
@@ -305,6 +337,13 @@ Execute(LSP tab completion requests should be sent):
 
   ALEGoToDefinitionInTab
 
+  " We shouldn't register the callback yet.
+  AssertEqual '''''', string(g:Callback)
+
+  AssertEqual type(function('type')), type(g:WaitCallback)
+  AssertEqual 'definition', g:capability_checked
+  call call(g:WaitCallback, [347, '/foo/bar'])
+
   AssertEqual
   \ 'function(''ale#definition#HandleLSPResponse'')',
   \ string(g:Callback)