feat(json): add abliity to remove trailing commas while stripping comments (#613)

Author: mehalter

lua/plenary/json.lua

@@ -33,20 +33,26 @@ local M = {}
 -- The resulting string can then be used by `vim.fn.json_decode`
 --
 ---@param jsonString string
----@param options table
+---@param options? table
 ---  * whitespace:
 ---     - defaults to true
 ---     - when true, comments will be replaced by whitespace
 ---     - when false, comments will be stripped
+---  * trailing_commas:
+---     - defaults to false
+---     - when true, trailing commas will be included
+---     - when false, trailing commas will be removed
 function M.json_strip_comments(jsonString, options)
   options = options or {}
   local strip = options.whitespace == false and stripWithoutWhitespace or stripWithWhitespace
+  local omitTrailingCommas = not options.trailing_commas
 
   local insideString = false
   local insideComment = false
   local offset = 1
   local result = ""
   local skip = false
+  local lastComma = 0
 
   for i = 1, #jsonString, 1 do
     if skip then
@@ -89,6 +95,16 @@ function M.json_strip_comments(jsonString, options)
           insideComment = false
           result = result .. strip(jsonString, offset, i)
           offset = i + 1
+        elseif omitTrailingCommas and not insideComment then
+          if currentCharacter == "," then
+            lastComma = i
+          elseif (currentCharacter == "]" or currentCharacter == "}") and lastComma > 0 then
+            result = result .. slice(jsonString, offset, lastComma - 1) .. slice(jsonString, lastComma + 1, i)
+            offset = i + 1
+            lastComma = 0
+          elseif currentCharacter:match "%S" then
+            lastComma = 0
+          end
         end
       end
     end

tests/plenary/json_spec.lua

@@ -67,4 +67,21 @@ describe("json", function()
       [[{"x":"x \"sed -e \\\"s/^.\\\\{46\\\\}T//\\\" -e \\\"s/#033/\\\\x1b/g\\\"\""}]]
     )
   end)
+
+  it("trailing commas", function()
+    eq(json.json_strip_comments '{"a":"b",}', '{"a":"b"}')
+    eq(json.json_strip_comments '{"a":{"b":"c",},}', '{"a":{"b":"c"}}')
+    eq(json.json_strip_comments '{"a":["b","c",],}', '{"a":["b","c"]}')
+  end)
+
+  it("trailing commas - ignored in strings and comments", function()
+    eq(json.json_strip_comments '{"a":"b,}"}', '{"a":"b,}"}')
+  end)
+
+  it("trailing commas - left when disabled in options", function()
+    local options = { trailing_commas = true }
+    eq(json.json_strip_comments('{"a":"b",}', options), '{"a":"b",}')
+    eq(json.json_strip_comments('{"a":{"b":"c",},}', options), '{"a":{"b":"c",},}')
+    eq(json.json_strip_comments('{"a":["b","c",],}', options), '{"a":["b","c",],}')
+  end)
 end)