Add support for finding references using LSP servers or tsserver

autoload/ale/lsp/message.vim

@@ -116,3 +116,13 @@ function! ale#lsp#message#Definition(buffer, line, column) abort
     \   'position': {'line': a:line - 1, 'character': a:column},
     \}]
 endfunction
+
+function! ale#lsp#message#References(buffer, line, column) abort
+    return [0, 'textDocument/references', {
+    \   'textDocument': {
+    \       'uri': ale#path#ToURI(expand('#' . a:buffer . ':p')),
+    \   },
+    \   'position': {'line': a:line - 1, 'character': a:column},
+    \   'context': {'includeDeclaration': v:false},
+    \}]
+endfunction

autoload/ale/lsp/tsserver_message.vim

@@ -61,3 +61,11 @@ function! ale#lsp#tsserver_message#Definition(buffer, line, column) abort
     \   'file': expand('#' . a:buffer . ':p'),
     \}]
 endfunction
+
+function! ale#lsp#tsserver_message#References(buffer, line, column) abort
+    return [0, 'ts@references', {
+    \   'line': a:line,
+    \   'offset': a:column,
+    \   'file': expand('#' . a:buffer . ':p'),
+    \}]
+endfunction

autoload/ale/references.vim

@@ -0,0 +1,111 @@
+let s:references_map = {}
+
+" Used to get the references map in tests.
+function! ale#references#GetMap() abort
+    return deepcopy(s:references_map)
+endfunction
+
+" Used to set the references map in tests.
+function! ale#references#SetMap(map) abort
+    let s:references_map = a:map
+endfunction
+
+function! ale#references#ClearLSPData() abort
+    let s:references_map = {}
+endfunction
+
+function! ale#references#HandleTSServerResponse(conn_id, response) abort
+    if get(a:response, 'command', '') is# 'references'
+    \&& has_key(s:references_map, a:response.request_seq)
+        call remove(s:references_map, a:response.request_seq)
+
+        if get(a:response, 'success', v:false) is v:true
+            let l:item_list = []
+
+            for l:response_item in a:response.body.refs
+                call add(l:item_list, {
+                \ 'filename': l:response_item.file,
+                \ 'line': l:response_item.start.line,
+                \ 'column': l:response_item.start.offset,
+                \})
+            endfor
+
+            if empty(l:item_list)
+                call ale#util#Execute('echom ''No references found.''')
+            else
+                call ale#preview#ShowSelection(l:item_list)
+            endif
+        endif
+    endif
+endfunction
+
+function! ale#references#HandleLSPResponse(conn_id, response) abort
+    if has_key(a:response, 'id')
+    \&& has_key(s:references_map, a:response.id)
+        call remove(s:references_map, a:response.id)
+
+        " The result can be a Dictionary item, a List of the same, or null.
+        let l:result = get(a:response, 'result', [])
+        let l:item_list = []
+
+        for l:response_item in l:result
+            call add(l:item_list, {
+            \ 'filename': ale#path#FromURI(l:response_item.uri),
+            \ 'line': l:response_item.range.start.line + 1,
+            \ 'column': l:response_item.range.start.character + 1,
+            \})
+        endfor
+
+        if empty(l:item_list)
+            call ale#util#Execute('echom ''No references found.''')
+        else
+            call ale#preview#ShowSelection(l:item_list)
+        endif
+    endif
+endfunction
+
+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')
+
+    let l:lsp_details = ale#linter#StartLSP(l:buffer, a:linter, l:Callback)
+
+    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#Send(l:id, ale#lsp#message#DidChange(l:buffer), l:root)
+
+        let l:column = min([l:column, len(getline(l:line))])
+
+        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:root)
+
+    let s:references_map[l:request_id] = {}
+endfunction
+
+function! ale#references#Find() abort
+    for l:linter in ale#linter#Get(&filetype)
+        if !empty(l:linter.lsp)
+            call s:FindReferences(l:linter)
+        endif
+    endfor
+endfunction