Support autocommands when LSP commands fail

This commit resolves issue 207. "Definition or references" can be implemented with the following:

```vim
autocmd User lsp_definition_failed LspReferences
```

I want to fall back to ctags when `LspDefinition` fails.

```vim
autocmd User lsp_definition_failed execute "tjump " . expand("<cword>")
```

Only commands/functions defined in `autoload/lsp/ui/vim.vim` are experimentally suppported.

Author: kg8m

autoload/lsp.vim

@@ -29,6 +29,17 @@ augroup _lsp_silent_
     autocmd User lsp_float_opened silent
     autocmd User lsp_float_closed silent
     autocmd User lsp_buffer_enabled silent
+    autocmd User lsp_implementation_failed silent
+    autocmd User lsp_type_definition_failed silent
+    autocmd User lsp_declaration_failed silent
+    autocmd User lsp_definition_failed silent
+    autocmd User lsp_references_failed silent
+    autocmd User lsp_rename_failed silent
+    autocmd User lsp_document_format_failed silent
+    autocmd User lsp_range_format_failed silent
+    autocmd User lsp_workspace_symbol_failed silent
+    autocmd User lsp_document_symbol_failed silent
+    autocmd User lsp_code_action_failed silent
 augroup END
 
 function! lsp#log_verbose(...) abort

autoload/lsp/ui/vim.vim

@@ -9,6 +9,7 @@ function! lsp#ui#vim#implementation(in_preview) abort
 
     if len(l:servers) == 0
         call s:not_supported('Retrieving implementation')
+        call s:after_failure('implementation')
         return
     endif
     let l:ctx = { 'counter': len(l:servers), 'list':[], 'last_command_id': l:command_id, 'jump_if_one': 1, 'in_preview': a:in_preview }
@@ -33,6 +34,7 @@ function! lsp#ui#vim#type_definition(in_preview) abort
 
     if len(l:servers) == 0
         call s:not_supported('Retrieving type definition')
+        call s:after_failure('type definition')
         return
     endif
     let l:ctx = { 'counter': len(l:servers), 'list':[], 'last_command_id': l:command_id, 'jump_if_one': 1, 'in_preview': a:in_preview }
@@ -83,6 +85,7 @@ function! lsp#ui#vim#declaration(in_preview) abort
 
     if len(l:servers) == 0
         call s:not_supported('Retrieving declaration')
+        call s:after_failure('declaration')
         return
     endif
 
@@ -108,6 +111,7 @@ function! lsp#ui#vim#definition(in_preview) abort
 
     if len(l:servers) == 0
         call s:not_supported('Retrieving definition')
+        call s:after_failure('definition')
         return
     endif
 
@@ -135,6 +139,7 @@ function! lsp#ui#vim#references() abort
     let l:ctx = { 'counter': len(l:servers), 'list':[], 'last_command_id': l:command_id, 'jump_if_one': 0, 'in_preview': 0 }
     if len(l:servers) == 0
         call s:not_supported('Retrieving references')
+        call s:after_failure('references')
         return
     endif
 
@@ -185,6 +190,7 @@ function! lsp#ui#vim#rename() abort
 
     if len(l:servers) == 0
         call s:not_supported('Renaming')
+        call s:after_failure('rename')
         return
     endif
 
@@ -212,6 +218,7 @@ function! s:document_format(sync) abort
 
     if len(l:servers) == 0
         call s:not_supported('Document formatting')
+        call s:after_failure('document format')
         return
     endif
 
@@ -292,6 +299,7 @@ function! s:document_format_range(sync, type) abort
 
     if len(l:servers) == 0
         call s:not_supported('Document range formatting')
+        call s:after_failure('range format')
         return
     endif
 
@@ -340,6 +348,7 @@ function! lsp#ui#vim#workspace_symbol() abort
 
     if len(l:servers) == 0
         call s:not_supported('Retrieving workspace symbols')
+        call s:after_failure('workspaceSymbol')
         return
     endif
 
@@ -370,6 +379,7 @@ function! lsp#ui#vim#document_symbol() abort
 
     if len(l:servers) == 0
         call s:not_supported('Retrieving symbols')
+        call s:after_failure('documentSymbol')
         return
     endif
 
@@ -393,6 +403,7 @@ function! s:handle_symbol(server, last_command_id, type, data) abort
 
     if lsp#client#is_error(a:data['response'])
         call lsp#utils#error('Failed to retrieve '. a:type . ' for ' . a:server . ': ' . lsp#client#error_message(a:data['response']))
+        call s:after_failure(a:type)
         return
     endif
 
@@ -402,6 +413,7 @@ function! s:handle_symbol(server, last_command_id, type, data) abort
 
     if empty(l:list)
         call lsp#utils#error('No ' . a:type .' found')
+        call s:after_failure(a:type)
     else
         echo 'Retrieved ' . a:type
         botright copen
@@ -417,13 +429,15 @@ function! s:handle_location(ctx, server, type, data) abort "ctx = {counter, list
 
     if lsp#client#is_error(a:data['response']) || !has_key(a:data['response'], 'result')
         call lsp#utils#error('Failed to retrieve '. a:type . ' for ' . a:server . ': ' . lsp#client#error_message(a:data['response']))
+        call s:after_failure(a:type)
     else
         let a:ctx['list'] = a:ctx['list'] + lsp#utils#location#_lsp_to_vim_list(a:data['response']['result'])
     endif
 
     if a:ctx['counter'] == 0
         if empty(a:ctx['list'])
             call lsp#utils#error('No ' . a:type .' found')
+            call s:after_failure(a:type)
         else
             call lsp#utils#tagstack#_update()
 
@@ -464,6 +478,7 @@ function! s:handle_rename_prepare(server, last_command_id, type, data) abort
 
     if lsp#client#is_error(a:data['response'])
         call lsp#utils#error('Failed to retrieve '. a:type . ' for ' . a:server . ': ' . lsp#client#error_message(a:data['response']))
+        call s:after_failure('rename')
         return
     endif
 
@@ -495,6 +510,7 @@ function! s:handle_workspace_edit(server, last_command_id, type, data) abort
 
     if lsp#client#is_error(a:data['response'])
         call lsp#utils#error('Failed to retrieve '. a:type . ' for ' . a:server . ': ' . lsp#client#error_message(a:data['response']))
+        call s:after_failure(a:type)
         return
     endif
 
@@ -510,6 +526,7 @@ function! s:handle_text_edit(server, last_command_id, type, data) abort
 
     if lsp#client#is_error(a:data['response'])
         call lsp#utils#error('Failed to '. a:type . ' for ' . a:server . ': ' . lsp#client#error_message(a:data['response']))
+        call s:after_failure(a:type)
         return
     endif
 
@@ -584,6 +601,14 @@ function! s:get_treeitem_for_tree_hierarchy(Callback, object) dict abort
     call a:Callback('success', s:hierarchyitem_to_treeitem(a:object))
 endfunction
 
+function! s:after_failure(type) abort
+  execute 'doautocmd User ' . s:event_name_on_failure(a:type)
+endfunction
+
+function! s:event_name_on_failure(type) abort
+  return 'lsp_' . substitute(substitute(a:type, '\s', '_', 'g'), '\C[A-Z]', '\="_" . tolower(submatch(0))', 'g') . '_failed'
+endfunction
+
 function! lsp#ui#vim#code_action() abort
     call lsp#ui#vim#code_action#do({
         \   'sync': v:false,

doc/vim-lsp.txt

@@ -1183,6 +1183,57 @@ This autocommand is run after vim-lsp is enabled for the buffer. This event is
 triggered imediately when the buffer is currently active. If the buffer is not
 current active, the event will be triggered when the buffer will be active.
 
+lsp_implementation_failed                        *lsp_implementation_failed*
+
+This autocommand is run after |LspImplementation| and |LspPeekImplementation|
+failed.
+
+lsp_type_definition_failed                      *lsp_type_definition_failed*
+
+This autocommand is run after |LspTypeDefinition| and |LspPeekTypeDefinition|
+failed.
+
+lsp_declaration_failed                              *lsp_declaration_failed*
+
+This autocommand is run after |LspDeclaration| and |LspPeekDeclaration|
+failed.
+
+lsp_definition_failed                                *lsp_definition_failed*
+
+This autocommand is run after |LspDefinition| and |LspPeekDefinition|
+failed.
+
+lsp_references_failed                                *lsp_references_failed*
+
+This autocommand is run after |LspReferences|, |LspNextReference| and
+|LspPreviousReference| failed.
+
+lsp_rename_failed                                        *lsp_rename_failed*
+
+This autocommand is run after |LspRename| failed.
+
+lsp_document_format_failed                      *lsp_document_format_failed*
+
+This autocommand is run after |LspDocumentFormat| and |LspDocumentFormatSync|
+failed.
+
+lsp_range_format_failed                            *lsp_range_format_failed*
+
+This autocommand is run after |LspDocumentRangeFormat| and
+|LspDocumentRangeFormatSync| failed.
+
+lsp_workspace_symbol_failed                    *lsp_workspace_symbol_failed*
+
+This autocommand is run after |LspWorkspaceSymbol| failed.
+
+lsp_document_symbol_failed                      *lsp_document_symbol_failed*
+
+This autocommand is run after |LspDocumentSymbol| failed.
+
+lsp_code_action_failed                              *lsp_code_action_failed*
+
+This autocommand is run after |LspCodeAction| failed.
+
 
 ==============================================================================
 Mappings                                                  *vim-lsp-mappings*