fix(diagnostic): remove useless highlight links (neovim#15683)

These links were actually defined backwards: the highlight groups
actually being used for display are the new "Diagnostic*" groups, so
linking the old "LspDiagnostics*" groups to these does absolutely
nothing, since there is nothing actually being highlighted with the
LspDiagnostics* groups.

These links were made in an attempt to preserve backward compatibility
with existing colorschemes. We could reverse the links to maintain this
preservation, but then that disallows us from actually defining default
values for the new highlight groups.

Instead, just remove the links and be done with the old LspDiagnostics*
highlight groups.

This is not technically a breaking change: the breaking change already
happened in neovim#15585, but this PR just makes that explicit.

runtime/lua/vim/lsp/diagnostic.lua

@@ -446,14 +446,6 @@ end
 ---
 ---@deprecated Prefer |vim.diagnostic._set_signs()|
 ---
---- Sign characters can be customized with the following commands:
----
---- <pre>
---- sign define LspDiagnosticsSignError text=E texthl=LspDiagnosticsSignError linehl= numhl=
---- sign define LspDiagnosticsSignWarning text=W texthl=LspDiagnosticsSignWarning linehl= numhl=
---- sign define LspDiagnosticsSignInformation text=I texthl=LspDiagnosticsSignInformation linehl= numhl=
---- sign define LspDiagnosticsSignHint text=H texthl=LspDiagnosticsSignHint linehl= numhl=
---- </pre>
 ---@param diagnostics Diagnostic[]
 ---@param bufnr number The buffer number
 ---@param client_id number the client id
@@ -478,15 +470,6 @@ end
 ---
 ---@deprecated Prefer |vim.diagnostic._set_underline()|
 ---
---- Underline highlights can be customized by changing the following |:highlight| groups.
----
---- <pre>
---- LspDiagnosticsUnderlineError
---- LspDiagnosticsUnderlineWarning
---- LspDiagnosticsUnderlineInformation
---- LspDiagnosticsUnderlineHint
---- </pre>
----
 ---@param diagnostics Diagnostic[]
 ---@param bufnr number: The buffer number
 ---@param client_id number: The client id
@@ -506,15 +489,6 @@ end
 ---
 ---@deprecated Prefer |vim.diagnostic._set_virtual_text()|
 ---
---- Virtual text highlights can be customized by changing the following |:highlight| groups.
----
---- <pre>
---- LspDiagnosticsVirtualTextError
---- LspDiagnosticsVirtualTextWarning
---- LspDiagnosticsVirtualTextInformation
---- LspDiagnosticsVirtualTextHint
---- </pre>
----
 ---@param diagnostics Diagnostic[]
 ---@param bufnr number
 ---@param client_id number

runtime/plugin/diagnostic.vim

@@ -24,25 +24,3 @@ hi default link DiagnosticSignError DiagnosticError
 hi default link DiagnosticSignWarn DiagnosticWarn
 hi default link DiagnosticSignInfo DiagnosticInfo
 hi default link DiagnosticSignHint DiagnosticHint
-
-" Link LspDiagnostics for backward compatibility
-hi default link LspDiagnosticsDefaultHint DiagnosticHint
-hi default link LspDiagnosticsVirtualTextHint DiagnosticVirtualTextHint
-hi default link LspDiagnosticsFloatingHint DiagnosticFloatingHint
-hi default link LspDiagnosticsSignHint DiagnosticSignHint
-hi default link LspDiagnosticsDefaultError DiagnosticError
-hi default link LspDiagnosticsVirtualTextError DiagnosticVirtualTextError
-hi default link LspDiagnosticsFloatingError DiagnosticFloatingError
-hi default link LspDiagnosticsSignError DiagnosticSignError
-hi default link LspDiagnosticsDefaultWarning DiagnosticWarn
-hi default link LspDiagnosticsVirtualTextWarning DiagnosticVirtualTextWarn
-hi default link LspDiagnosticsFloatingWarning DiagnosticFloatingWarn
-hi default link LspDiagnosticsSignWarning DiagnosticSignWarn
-hi default link LspDiagnosticsDefaultInformation DiagnosticInfo
-hi default link LspDiagnosticsVirtualTextInformation DiagnosticVirtualTextInfo
-hi default link LspDiagnosticsFloatingInformation DiagnosticFloatingInfo
-hi default link LspDiagnosticsSignInformation DiagnosticSignInfo
-hi default link LspDiagnosticsUnderlineError DiagnosticUnderlineError
-hi default link LspDiagnosticsUnderlineWarning DiagnosticUnderlineWarn
-hi default link LspDiagnosticsUnderlineInformation DiagnosticUnderlineInfo
-hi default link LspDiagnosticsUnderlineHint DiagnosticUnderlineHint

test/functional/plugin/lsp/diagnostic_spec.lua

@@ -1,6 +1,5 @@
 local helpers = require('test.functional.helpers')(after_each)
 
-local command = helpers.command
 local clear = helpers.clear
 local exec_lua = helpers.exec_lua
 local eq = helpers.eq
@@ -945,31 +944,4 @@ describe('vim.lsp.diagnostic', function()
       assert(loc_list[1].lnum < loc_list[2].lnum)
     end)
   end)
-
-  it('highlight groups', function()
-    command('runtime plugin/diagnostic.vim')
-    eq({
-      'LspDiagnosticsDefaultError',
-      'LspDiagnosticsDefaultHint',
-      'LspDiagnosticsDefaultInformation',
-      'LspDiagnosticsDefaultWarning',
-      'LspDiagnosticsFloatingError',
-      'LspDiagnosticsFloatingHint',
-      'LspDiagnosticsFloatingInformation',
-      'LspDiagnosticsFloatingWarning',
-      'LspDiagnosticsSignError',
-      'LspDiagnosticsSignHint',
-      'LspDiagnosticsSignInformation',
-      'LspDiagnosticsSignWarning',
-      'LspDiagnosticsUnderlineError',
-      'LspDiagnosticsUnderlineHint',
-      'LspDiagnosticsUnderlineInformation',
-      'LspDiagnosticsUnderlineWarning',
-      'LspDiagnosticsVirtualTextError',
-      'LspDiagnosticsVirtualTextHint',
-      'LspDiagnosticsVirtualTextInformation',
-      'LspDiagnosticsVirtualTextWarning',
-    }, exec_lua([[return vim.fn.getcompletion('Lsp', 'highlight')]]))
-  end)
-
 end)