fix(vim.json): loss of precision on integers >14 digits #34876

Problem: multiple DAP servers keep assuming they can have internal IDs
         up to 2**52, which get corrupted by the Neovim JSON encoder.
Solution: change (1) constant and add a test so nobody breaks it while
          updating the library.

Fixes: https://github.com/neovim/neovim/issues/24532
Fixes: https://github.com/mfussenegger/nvim-dap/issues/1534
Fixes: https://github.com/facebook/buck2/issues/1032

src/cjson/lua_cjson.c

@@ -82,7 +82,7 @@
 #define DEFAULT_ENCODE_INVALID_NUMBERS 0
 #define DEFAULT_DECODE_INVALID_NUMBERS 1
 #define DEFAULT_ENCODE_KEEP_BUFFER 1
-#define DEFAULT_ENCODE_NUMBER_PRECISION 14
+#define DEFAULT_ENCODE_NUMBER_PRECISION 16
 #define DEFAULT_ENCODE_EMPTY_TABLE_AS_OBJECT 0
 #define DEFAULT_DECODE_ARRAY_WITH_ARRAY_MT 0
 #define DEFAULT_ENCODE_ESCAPE_FORWARD_SLASH 1

test/functional/lua/json_spec.lua

@@ -77,6 +77,7 @@ describe('vim.json.decode()', function()
     eq(-100000, exec_lua([[return vim.json.decode('  -100000  ')]]))
     eq(0, exec_lua([[return vim.json.decode('0')]]))
     eq(0, exec_lua([[return vim.json.decode('-0')]]))
+    eq(3053700806959403, exec_lua([[return vim.json.decode('3053700806959403')]]))
   end)
 
   it('parses floating-point numbers', function()
@@ -208,6 +209,7 @@ describe('vim.json.encode()', function()
   end)
 
   it('dumps floats', function()
+    eq('3053700806959403', exec_lua([[return vim.json.encode(3053700806959403)]]))
     eq('10.5', exec_lua([[return vim.json.encode(10.5)]]))
     eq('-10.5', exec_lua([[return vim.json.encode(-10.5)]]))
     eq('-1e-05', exec_lua([[return vim.json.encode(-1e-5)]]))