Diag Type for Invalid Characters in Config

docs/errors/E0292.md

@@ -0,0 +1,33 @@
+# E0292: character is not allowed in global identifiers
+
+Certain characters generate errors when used in JSON global variables in config files, such as the ```.``` below.
+
+```example-invalid-period
+{
+  "globals": {
+    "jest.": true
+  }
+}
+```
+
+Leading spaces and numbers are also disallowed:
+
+```example-invalid-nums
+{ 
+  "globals": { 
+    "123ABC": true 
+  } 
+}
+```
+
+As are certain unicode characters:
+
+```example-invalid-unicode
+{ 
+  "globals": { 
+    "\u2604": true 
+  } 
+}
+```
+
+To fix this error, rename variables to exclude disallowed characters and leading numbers or spaces.

src/quick-lint-js/fe/diagnostic-types.h

@@ -346,6 +346,13 @@
           QLJS_TRANSLATABLE("commas are not allowed between class methods"),   \
           unexpected_comma))                                                   \
                                                                                \
+  QLJS_DIAG_TYPE(                                                              \
+    diag_config_character_disallowed_in_identifiers, "E0292",                  \
+    diagnostic_severity::error, { source_code_span character; },               \
+    MESSAGE(                                                                   \
+          QLJS_TRANSLATABLE("character is not allowed in global identifiers"), \
+          character))                                                          \
+                                                                               \
   QLJS_DIAG_TYPE(                                                              \
       diag_config_json_syntax_error, "E0164", diagnostic_severity::error,      \
       { source_code_span where; },                                             \