fix(filter): anchor zero-width diagnostics at col and col-1 (#179)

Author: rachartier

lua/tiny-inline-diagnostic/filter.lua

@@ -34,7 +34,16 @@ function M.at_position(opts, diagnostics, line, col)
   end
 
   local current_pos_diags = vim.tbl_filter(function(diag)
-    return diag.lnum == line and col >= diag.col and col <= diag.end_col
+    if diag.lnum ~= line then
+      return false
+    end
+
+    -- Zero-width LSP range (Range.end exclusive, start == end): anchor to the
+    -- character on either side of the point so end-of-token diagnostics match
+    if diag.col == diag.end_col and diag.col > 0 then
+      return col == diag.col or col == diag.col - 1
+    end
+    return col >= diag.col and col <= diag.end_col
   end, diagnostics)
 
   if opts.options.show_diags_only_under_cursor then

tests/test_filter.lua

@@ -118,6 +118,18 @@ T["at_position"]["show_diags_only_under_cursor merges whole-line and under-curso
   MiniTest.expect.equality(#result, 2)
 end
 
+T["at_position"]["zero-width diagnostic matches cursor at col and col-1"] = function()
+  local diagnostics = {
+    H.make_diagnostic({ lnum = 5, col = 33, end_col = 33 }),
+  }
+  local opts = { options = { show_diags_only_under_cursor = true } }
+
+  MiniTest.expect.equality(#filter.at_position(opts, diagnostics, 5, 32), 1)
+  MiniTest.expect.equality(#filter.at_position(opts, diagnostics, 5, 33), 1)
+  MiniTest.expect.equality(#filter.at_position(opts, diagnostics, 5, 31), 0)
+  MiniTest.expect.equality(#filter.at_position(opts, diagnostics, 5, 34), 0)
+end
+
 T["under_cursor"] = MiniTest.new_set()
 
 T["under_cursor"]["returns empty for invalid buffer"] = function()