From d5dd0aa1e633691ea6fa9b366b366a0a13cf7eba Mon Sep 17 00:00:00 2001
From: Gregory Anders <8965202+gpanders@users.noreply.github.com>
Date: Fri, 8 Oct 2021 12:28:02 -0600
Subject: [PATCH] fix(diagnostic): error on invalid severity value (#15965)

Users can pass string values for severities that match with the enum
names (e.g. "Warn" or "Info") which are converted to the corresponding
numerical value in `to_severity`. Invalid strings were simply left
as-is, which caused confusing errors later on. Instead, report an
invalid severity string right up front to make the problem clear.
---
 runtime/lua/vim/diagnostic.lua | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/runtime/lua/vim/diagnostic.lua b/runtime/lua/vim/diagnostic.lua
index b58055f07e..e8aba6b7a3 100644
--- a/runtime/lua/vim/diagnostic.lua
+++ b/runtime/lua/vim/diagnostic.lua
@@ -27,7 +27,10 @@ local global_diagnostic_options = {
 
 ---@private
 local function to_severity(severity)
-  return type(severity) == 'string' and M.severity[string.upper(severity)] or severity
+  if type(severity) == 'string' then
+    return assert(M.severity[string.upper(severity)], string.format("Invalid severity: %s", severity))
+  end
+  return severity
 end
 
 ---@private