Metals returns snippets even when a client doesn't support them

[bstaletic]

Describe the bug

The protocol doesn't require clients to support snippet completion. For those clients, the servers are supposed to only provide plain text completion.

One such client is ycmd, whose capabilities you can see here
As you can see, the capabilities don't contain { 'completionItem': { 'snippetSupport': True } } and, according to the protocol, the lack of 'snippetSupport' is supposed to be treated as 'snippetSupport': False.

Unfortunately, completion request returns:

2019-11-09 00:13:32,982 - DEBUG - RX: Received message: b'{"jsonrpc":"2.0","id":20,"result":{"isIncomplete":false,"items":[{"label":"getRemoteEndpoint(): RemoteEndpoint","kind":8,"detail":"(): RemoteEndpoint","preselect":true,"sortText":"00000","filterText":"getRemoteEndpoint","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"getRemoteEndpoint"},"data":{"symbol":"org/eclipse/lsp4j/jsonrpc/Launcher#getRemoteEndpoint().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"getRemoteProxy(): MetalsLanguageClient","kind":8,"detail":"(): MetalsLanguageClient","sortText":"00001","filterText":"getRemoteProxy","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"getRemoteProxy"},"data":{"symbol":"org/eclipse/lsp4j/jsonrpc/Launcher#getRemoteProxy().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"startListening(): Future[Void]","kind":8,"detail":"(): Future[Void]","sortText":"00002","filterText":"startListening","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":29}},"newText":"startListening"},"data":{"symbol":"org/eclipse/lsp4j/jsonrpc/Launcher#startListening().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"+(other: String): String","kind":2,"detail":"(other: String): String","sortText":"00003","filterText":"+","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"+"},"data":{"symbol":"scala/Predef.any2stringadd#`+`().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"formatted(fmtstr: String): String","kind":2,"detail":"(fmtstr: String): String","sortText":"00004","filterText":"formatted","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"formatted"},"data":{"symbol":"scala/Predef.StringFormat#formatted().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"parse[U](implicit convert: Convert[Launcher[MetalsLanguageClient],Input], parse: Parse[U], dialect: Dialect): Parsed[U]","kind":2,"detail":"[U](implicit convert: Convert[Launcher[MetalsLanguageClient],Input], parse: Parse[U], dialect: Dialect): Parsed[U]","sortText":"00005","filterText":"parse","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"parse"},"data":{"symbol":"scala/meta/parsers/Api#XtensionParseInputLike#parse().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"show[Style[X] \\u003c: scala.meta.prettyprinters.Show[X]](implicit style: Style[Launcher[MetalsLanguageClient]]): String","kind":2,"detail":"[Style[X] \\u003c: scala.meta.prettyprinters.Show[X]](implicit style: Style[Launcher[MetalsLanguageClient]]): String","sortText":"00006","filterText":"show","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"show"},"data":{"symbol":"scala/meta/prettyprinters/Api#XtensionShow#show().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"tokenize(implicit convert: Convert[Launcher[MetalsLanguageClient],Input], tokenize: Tokenize, dialect: Dialect): Tokenized","kind":2,"detail":"(implicit convert: Convert[Launcher[MetalsLanguageClient],Input], tokenize: Tokenize, dialect: Dialect): Tokenized","sortText":"00007","filterText":"tokenize","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"tokenize"},"data":{"symbol":"scala/meta/tokenizers/Api#XtensionTokenizeInputLike#tokenize().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"asInstanceOf[T0]: T0","kind":2,"detail":"[T0]: T0","sortText":"00008","filterText":"asInstanceOf","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"asInstanceOf"},"data":{"symbol":"scala/Any#asInstanceOf().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"equals(x$1: Any): Boolean","kind":8,"detail":"(x$1: Any): Boolean","sortText":"00009","filterText":"equals","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"equals"},"data":{"symbol":"java/lang/Object#equals().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"getClass(): Class[_]","kind":8,"detail":"(): Class[_]","sortText":"00010","filterText":"getClass","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"getClass"},"data":{"symbol":"java/lang/Object#getClass().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"hashCode(): Int","kind":8,"detail":"(): Int","sortText":"00011","filterText":"hashCode","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"hashCode"},"data":{"symbol":"java/lang/Object#hashCode().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"isInstanceOf[T0]: Boolean","kind":2,"detail":"[T0]: Boolean","sortText":"00012","filterText":"isInstanceOf","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"isInstanceOf"},"data":{"symbol":"scala/Any#isInstanceOf().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"synchronized[T0](x$1: T0): T0","kind":2,"detail":"[T0](x$1: T0): T0","sortText":"00013","filterText":"synchronized","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"synchronized"},"data":{"symbol":"java/lang/Object#synchronized().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}},{"label":"toString(): String","kind":8,"detail":"(): String","sortText":"00014","filterText":"toString","insertTextFormat":2,"textEdit":{"range":{"start":{"line":43,"character":15},"end":{"line":43,"character":15}},"newText":"toString"},"data":{"symbol":"java/lang/Object#toString().","target":"file:/home/bstaletic/aur/metals/src/metals-0.7.6/metals/?id\\u003dmetals"}}]}}'

The completion items contain "inserTextFormat":2, which indicates snippets and triggers an assert in ycmd.

To Reproduce
Steps to reproduce the behavior:

1. Install YouCompleteMe for vim
2. Unfortunately, ycmd still doesn't support showMessageRequest, so one will need to apply this patch.
3. Put let g:ycm_language_server = [ { 'name': 'metals-showMessageRequest', 'filetypes': [ 'scala', 'sbt' ], 'cmdline': [ 'metals-vim' ], 'project_root_files': [ 'build.sbt' ] } ] in your vimrc.
4. Open a scala file and wait for metals to finish building
5. Try to complete
6. The stack trace of the assert can be found in one of the logs visible in :YcmDebugInfo.

Expected behavior

Screenshots

Installation:

• Operating system: Linux
• Editor: Vim with YouCompleteMe
• Metals version: v0.7.6

Additional context

Search terms

[tgodzik]

Thanks for reporting! We do have snippets in a couple of places, it should be easy configure Metals not send them in the cases that the client doesn't support them.

[gabro]

@bstaletic thanks for the detailed bug report! 🙏 #1057 contains a pending fix for this

[bstaletic]

@gabro Thanks for taking a look at this. To be honest, I wasn't expecting such a quick PR. I'll test the PR tomorrow and report how it works with ycmd.