fix(diagnostic): remove invalid buffers from cache (#16397)

Errors were being caused by invalid buffers being kept around in
diagnostic_cache, so add a metatable to diagnostic_cache which attaches
to new buffers in the cache, removing them after they are invalidated.

Closes #16391.

Co-authored-by: Gregory Anders <8965202+gpanders@users.noreply.github.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/test/functional/lua/diagnostic_spec.lua b/test/functional/lua/diagnostic_spec.lua
index cdf9a8a834..348b9de816 100644
--- a/test/functional/lua/diagnostic_spec.lua
+++ b/test/functional/lua/diagnostic_spec.lua
@@ -343,6 +343,16 @@ describe('vim.diagnostic', function()
       eq(0, result[5])
       eq(3, result[6])
     end)
+
+    it("doesn't error after bwipeout on buffer", function()
+      exec_lua [[
+        vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, { lnum = 0, end_lnum = 0, col = 0, end_col = 0 })
+        vim.cmd("bwipeout! " .. diagnostic_bufnr)
+
+        vim.diagnostic.show(diagnostic_ns)
+        vim.diagnostic.hide(diagnostic_ns)
+      ]]
+    end)
   end)
 
   describe('enable() and disable()', function()
@@ -629,6 +639,15 @@ describe('vim.diagnostic', function()
       ]])
 
     end)
+
+    it("doesn't error after bwipeout called on buffer", function()
+      exec_lua [[
+        vim.diagnostic.set(diagnostic_ns, diagnostic_bufnr, { lnum = 0, end_lnum = 0, col = 0, end_col = 0 })
+        vim.cmd("bwipeout! " .. diagnostic_bufnr)
+
+        vim.diagnostic.reset(diagnostic_ns)
+      ]]
+    end)
   end)
 
   describe('get_next_pos()', function()