Texlab sends snippets in completion response even when client doesn't claim support

According to the protocol, the server may only respond to textDocument/completion request with snippets (indicated with insertTextFormat == 2) if the client had claimed snippet support in the initial initialize request. However texlab doesn't respect that.

https://microsoft.github.io/language-server-protocol/specification#textDocument_completion

export interface CompletionClientCapabilities {
    /**
     * The client supports the following `CompletionItem` specific
     * capabilities.
     */
    completionItem?: {
        /**
         * Client supports snippets as insert text.
         *
         * A snippet can define tab stops and placeholders with `$1`, `$2`
         * and `${3:foo}`. `$0` defines the final tab stop, it defaults to
         * the end of the snippet. Placeholders with equal identifiers are
         * linked, that is typing in one will update others too.
         */
        snippetSupport?: boolean;
        }
}
export namespace InsertTextFormat {
    export const PlainText = 1;
    export const Snippet = 2;
}
export type InsertTextFormat = 1 | 2;

Here are the exchanged messages between texlab and ycmd, which doesn't support snippets:

2021-05-13 14:47:31,259 - DEBUG - TX: Sending message: b'Content-Length: 1232\r\n\r\n{"id":1,"jsonrpc":"2.0","method":"initialize","params":{"capabilities":{"textDocument":{"codeAction":{"codeActionLiteralSupport":{"codeActionKind":{"valueSet":["","quickfix","refactor","refactor.extract","refactor.inline","refactor.rewrite","source","source.organizeImports"]}}},"completion":{"completionItem":{"documentationFormat":["plaintext","markdown"]},"completionItemKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]}},"documentSymbol":{"hierarchicalDocumentSymbolSupport":false,"labelSupport":false,"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]}},"hover":{"contentFormat":["plaintext","markdown"]},"signatureHelp":{"signatureInformation":{"documentationFormat":["plaintext","markdown"],"parameterInformation":{"labelOffsetSupport":true}}},"synchronization":{"didSave":true}},"workspace":{"applyEdit":true,"didChangeWatchedFiles":{"dynamicRegistration":true},"symbol":{"symbolKind":{"valueSet":[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]}},"workspaceEdit":{"documentChanges":true}}},"initializationOptions":{},"processId":9646,"rootPath":"/home/bstaletic/work/test","rootUri":"file:///home/bstaletic/work/test"}}'
2021-05-13 14:47:31,331 - DEBUG - RX: Received message: b'{"jsonrpc":"2.0","result":{"capabilities":{"completionProvider":{"resolveProvider":true,"triggerCharacters":["\\\\","{","}","@","/"," "]},"definitionProvider":true,"documentFormattingProvider":true,"documentHighlightProvider":true,"documentLinkProvider":{"resolveProvider":false},"documentSymbolProvider":true,"foldingRangeProvider":true,"hoverProvider":true,"referencesProvider":true,"renameProvider":{"prepareProvider":true},"textDocumentSync":{"change":1,"openClose":true,"save":{"includeText":false}},"workspaceSymbolProvider":true},"serverInfo":{"name":"TexLab","version":"2.2.2"}},"id":1}'
2021-05-13 14:47:31,332 - DEBUG - TX: Sending notification: b'Content-Length: 52\r\n\r\n{"jsonrpc":"2.0","method":"initialized","params":{}}'
2021-05-13 14:47:31,332 - DEBUG - TX: Sending notification: b'Content-Length: 86\r\n\r\n{"jsonrpc":"2.0","method":"workspace/didChangeConfiguration","params":{"settings":{}}}'
2021-05-13 14:47:31,333 - DEBUG - TX: Sending notification: b'Content-Length: 572\r\n\r\n{"jsonrpc":"2.0","method":"textDocument/didOpen","params":{"textDocument":{"languageId":"tex","text":"\\\\documentclass[aps,pre,superscriptaddress]{revtex4-1}\\n\\\\usepackage{amssymb}\\n\\\\usepackage{amsmath}\\n\\\\usepackage{color}\\n\\\\begin{document}\\n\\\\title{Life, the Universe and Everything }\\n\\\\author{Douglas Adams}\\n\\\\begin{abstract}\\n42 is the answer\\n\\\\end{abstract}\\n\\\\date{\\\\today}\\n\\\\maketitle\\n\\\\section{Introduction}\\nbla bla\\n\\\\begin{eqnarray}\\n  x&=&y\\\\\\\\\\n  y&=&2\\n\\\\end{eqnarray}\\n\\\\end{document}\\n","uri":"file:///home/bstaletic/work/test/foo.tex","version":1}}}'
2021-05-13 14:47:35,067 - DEBUG - TX: Sending message: b'Content-Length: 172\r\n\r\n{"id":2,"jsonrpc":"2.0","method":"textDocument/completion","params":{"position":{"character":1,"line":7},"textDocument":{"uri":"file:///home/bstaletic/work/test/foo.tex"}}}'
2021-05-13 14:47:35,069 - DEBUG - RX: Received message: b'{"jsonrpc":"2.0","result":{"isIncomplete":false,"items":[{"data":"commandSnippet","detail":"built-in","insertText":"begin{$1}\\n\\t$0\\n\\\\end{$1}","insertTextFormat":2,"kind":15,"label":"begin","preselect":false,"sortText":"00"},{"data":"command","detail":"built-in","kind":3,"label":"begingroup","preselect":false,"sortText":"01","textEdit":{"newText":"begingroup","range":{"end":{"character":6,"line":7},"start":{"character":1,"line":7}}}},{"data":"command","detail":"built-in","kind":3,"label":"AtBeginDocument","preselect":false,"sortText":"02","textEdit":{"newText":"AtBeginDocument","range":{"end":{"character":6,"line":7},"start":{"character":1,"line":7}}}},{"data":"command","detail":"built-in","kind":3,"label":"AtBeginDvi","preselect":false,"sortText":"03","textEdit":{"newText":"AtBeginDvi","range":{"end":{"character":6,"line":7},"start":{"character":1,"line":7}}}}]},"id":2}'

That completion response ends up causing an assertion error and users see no completions.

latex-lsp / texlab

Texlab sends snippets in completion response even when client doesn't claim support #413