Update: globals configuration support readonly/writable/off (fixes es…

…lint#9940)

lib/linter.js

@@ -170,6 +170,19 @@ function parseListConfig(string) {
     return items;
 }
 
+/**
+ * normize globals config to new-style:
+ * - readonly: to indicate that a global is read-only (same as false)
+ * - writable: to indicate that a global is writable (same as true)
+ * - off: to indicate that a global is not present
+ * @param {boolean|string} config The given global config, can be old-style: true/false
+ * @returns {string} normalized new-style globals
+ */
+function normalizeGlobalConfig(config) {
+    return config === true ? "writable" // eslint-disable-line no-nested-ternary
+        : (config === false ? "readonly" : config);
+}
+
 /**
  * Ensures that variables representing built-in properties of the Global Object,
  * and any globals declared by special block comments, are present in the global
@@ -189,7 +202,7 @@ function addDeclaredGlobals(globalScope, configGlobals, commentDirectives) {
             globalScope.variables.push(variable);
             globalScope.set.set(name, variable);
         }
-        variable.writeable = configGlobals[name];
+        variable.config = normalizeGlobalConfig(configGlobals[name]);
     });
 
     Object.keys(commentDirectives.enabledGlobals).forEach(name => {
@@ -202,7 +215,7 @@ function addDeclaredGlobals(globalScope, configGlobals, commentDirectives) {
             globalScope.variables.push(variable);
             globalScope.set.set(name, variable);
         }
-        variable.writeable = commentDirectives.enabledGlobals[name].value;
+        variable.config = normalizeGlobalConfig(commentDirectives.enabledGlobals[name].value);
     });
 
     // mark all exported variables as such