json: make error messages more readable

Print tokens themselves instead of token names "T_*" in the error
messages.

Part of #4339

test/app-tap/json.test.lua

@@ -22,7 +22,7 @@ end
 
 tap.test("json", function(test)
     local serializer = require('json')
-    test:plan(40)
+    test:plan(51)
 
     test:test("unsigned", common.test_unsigned, serializer)
     test:test("signed", common.test_signed, serializer)
@@ -154,4 +154,34 @@ tap.test("json", function(test)
     _, err_msg = pcall(serializer.decode, '{"hello": "world",\n 100: 200}')
     test:ok(string.find(err_msg, 'line 2 at character 2') ~= nil,
             'mistake on second line')
+
+    --
+    -- gh-4339: Make sure that tokens 'T_*' are absent in error
+    -- messages and a context is printed.
+    --
+    _, err_msg = pcall(serializer.decode, '{{: "world"}')
+    test:ok(string.find(err_msg, '\'{\'') ~= nil, '"{" instead of T_OBJ_BEGIN')
+    _, err_msg = pcall(serializer.decode, '{"a": "world"}}')
+    test:ok(string.find(err_msg, '\'}\'') ~= nil, '"}" instead of T_OBJ_END')
+    _, err_msg = pcall(serializer.decode, '{[: "world"}')
+    test:ok(string.find(err_msg, '\'[\'', 1, true) ~= nil,
+            '"[" instead of T_ARR_BEGIN')
+    _, err_msg = pcall(serializer.decode, '{]: "world"}')
+    test:ok(string.find(err_msg, '\']\'', 1, true) ~= nil,
+            '"]" instead of T_ARR_END')
+    _, err_msg = pcall(serializer.decode, '{1: "world"}')
+    test:ok(string.find(err_msg, 'int') ~= nil, 'int instead of T_INT')
+    _, err_msg = pcall(serializer.decode, '{1.0: "world"}')
+    test:ok(string.find(err_msg, 'number') ~= nil, 'number instead of T_NUMBER')
+    _, err_msg = pcall(serializer.decode, '{true: "world"}')
+    test:ok(string.find(err_msg, 'boolean') ~= nil,
+            'boolean instead of T_BOOLEAN')
+    _, err_msg = pcall(serializer.decode, '{null: "world"}')
+    test:ok(string.find(err_msg, 'null') ~= nil, 'null instead of T_NULL')
+    _, err_msg = pcall(serializer.decode, '{:: "world"}')
+    test:ok(string.find(err_msg, 'colon') ~= nil, 'colon instead of T_COLON')
+    _, err_msg = pcall(serializer.decode, '{,: "world"}')
+    test:ok(string.find(err_msg, 'comma') ~= nil, 'comma instead of T_COMMA')
+    _, err_msg = pcall(serializer.decode, '{')
+    test:ok(string.find(err_msg, 'end') ~= nil, 'end instead of T_END')
 end)

third_party/lua-cjson/lua_cjson.c

@@ -75,23 +75,23 @@ typedef enum {
 } json_token_type_t;
 
 static const char *json_token_type_name[] = {
-    "T_OBJ_BEGIN",
-    "T_OBJ_END",
-    "T_ARR_BEGIN",
-    "T_ARR_END",
-    "T_STRING",
-    "T_UINT",
-    "T_INT",
-    "T_NUMBER",
-    "T_BOOLEAN",
-    "T_NULL",
-    "T_COLON",
-    "T_COMMA",
-    "T_END",
-    "T_WHITESPACE",
-    "T_LINEFEED",
-    "T_ERROR",
-    "T_UNKNOWN",
+    "'{'",
+    "'}'",
+    "'['",
+    "']'",
+    "string",
+    "unsigned int",
+    "int",
+    "number",
+    "boolean",
+    "null",
+    "colon",
+    "comma",
+    "end",
+    "whitespace",
+    "line feed",
+    "error",
+    "unknown symbol",
     NULL
 };
 
@@ -920,7 +920,7 @@ static void json_parse_object_context(lua_State *l, json_parse_t *json)
         }
 
         if (token.type != T_COMMA)
-            json_throw_parse_error(l, json, "comma or object end", &token);
+            json_throw_parse_error(l, json, "comma or '}'", &token);
 
         json_next_token(json, &token);
     }
@@ -960,7 +960,7 @@ static void json_parse_array_context(lua_State *l, json_parse_t *json)
         }
 
         if (token.type != T_COMMA)
-            json_throw_parse_error(l, json, "comma or array end", &token);
+            json_throw_parse_error(l, json, "comma or ']'", &token);
 
         json_next_token(json, &token);
     }