bug#62694: 30.0.50; eglot-tests fails with recent pylsp

[Michael Albinus <michael.albinus@gmx.de>]

Eli Zaretskii <eliz@gnu.org> writes:

Hi,

> A version test doesn't have to mean literally testing the version.  It
> can be a different test, specifically for the problematic behavior.
> If we understand the problematic behavior, we can test for it.  (If we
> don't understand the problem, how do we know it is in the server and
> not in Eglot or elsewhere in Emacs?)

I have done the homework (not mine!) and compared passing and failing
eglot-tests. For that I have compared the failing tests from Emba, and
the passing tests on my laptop, running Fedora 37. I have compared test
case eglot-test-basic-completions.

The initialization handshake is identical, except the server info. On
Emba, the server reports

--8<---------------cut here---------------start------------->8---
[server-reply] (id:1) Fri Apr  7 01:05:39 2023:
(:jsonrpc "2.0" :id 1 :result
	  (:capabilities
	   (:codeActionProvider t :codeLensProvider
				(:resolveProvider :json-false)
				:completionProvider
				(:resolveProvider t :triggerCharacters
						  ["."])
				:documentFormattingProvider t :documentHighlightProvider t :documentRangeFormattingProvider t :documentSymbolProvider t :definitionProvider t :executeCommandProvider
				(:commands
				 [])
				:hoverProvider t :referencesProvider t :renameProvider t :foldingRangeProvider t :signatureHelpProvider
				(:triggerCharacters
				 ["(" "," "="])
				:textDocumentSync
				(:change 2 :save
					 (:includeText t)
					 :openClose t)
				:workspace
				(:workspaceFolders
				 (:supported t :changeNotifications t))
				:experimental nil)
	   :serverInfo
	   (:name "pylsp" :version "1.7.1")))
--8<---------------cut here---------------end--------------->8---

On my laptop, there is an older server version:

--8<---------------cut here---------------start------------->8---
[server-reply] (id:1) Fri Apr  7 13:30:45 2023:
(:jsonrpc "2.0" :id 1 :result
	  (:capabilities
	   (:codeActionProvider t :codeLensProvider
				(:resolveProvider :json-false)
				:completionProvider
				(:resolveProvider t :triggerCharacters
						  ["."])
				:documentFormattingProvider t :documentHighlightProvider t :documentRangeFormattingProvider t :documentSymbolProvider t :definitionProvider t :executeCommandProvider
				(:commands
				 [])
				:hoverProvider t :referencesProvider t :renameProvider t :foldingRangeProvider t :signatureHelpProvider
				(:triggerCharacters
				 ["(" "," "="])
				:textDocumentSync
				(:change 2 :save
					 (:includeText t)
					 :openClose t)
				:workspace
				(:workspaceFolders
				 (:supported t :changeNotifications t))
				:experimental nil)
	   :serverInfo
	   (:name "pylsp" :version "1.4.1")))
--8<---------------cut here---------------end--------------->8---

The interesting difference is the following dialogue. The client request
is identical on both machines (expcept the temporary file name):

--8<---------------cut here---------------start------------->8---
[client-request] (id:2) Fri Apr  7 13:30:45 2023:
(:jsonrpc "2.0" :id 2 :method "textDocument/completion" :params
	  (:textDocument
	   (:uri "file:///tmp/eglot--fixturepBX5M9/project/something.py")
	   :position
	   (:line 1 :character 7)
	   :context
	   (:triggerKind 1)))
--8<---------------cut here---------------end--------------->8---

The server reply on my laptop is

--8<---------------cut here---------------start------------->8---
[server-reply] (id:2) Fri Apr  7 13:30:46 2023:
(:jsonrpc "2.0" :id 2 :result
	  (:isIncomplete :json-false :items
			 [(:label "exit(status)" :kind 3 :sortText "aexit" :insertText "exit" :data
				  (:doc_uri "file:///tmp/eglot--fixturepBX5M9/project/something.py"))]))
[client-notification] Fri Apr  7 13:30:46 2023:
(:jsonrpc "2.0" :method "textDocument/didChange" :params
	  (:textDocument
	   (:uri "file:///tmp/eglot--fixturepBX5M9/project/something.py" :version 1)
	   :contentChanges
	   [(:range
	     (:start
	      (:line 1 :character 7)
	      :end
	      (:line 1 :character 7))
	     :rangeLength 0 :text "t")]))
--8<---------------cut here---------------end--------------->8---

But on Emba, we see only

--8<---------------cut here---------------start------------->8---
[server-reply] (id:2) Fri Apr  7 01:05:39 2023:
(:jsonrpc "2.0" :id 2 :result
	  (:isIncomplete :json-false :items
			 []))
[server-notification] Fri Apr  7 01:05:40 2023:
(:jsonrpc "2.0" :method "textDocument/publishDiagnostics" :params
	  (:uri "file:///tmp/eglot--fixture5UoqLl/project/something.py" :diagnostics
		[]))
--8<---------------cut here---------------end--------------->8---

So a different reply, with less information.

> Well, how about coding the test Michael asked, and I seconded, then?
> I agree that it will be a much better use of our time than keeping
> arguing about it.

I have absolutely no idea about the language server protocol, and
whether both server replies are valid communication. If both are valid,
eglot shall support this.

If not, I believe eglot shall raise an error like "protocol mismatch",
and eglot-tests could catch this error and use it as indication that the
test has to be skipped, with a respective skip message.

> TIA

Best regards, Michael.