Add runtime check for 'ts.unescapeIdentifier()' presence

src/rules/noStringLiteralRule.ts

@@ -42,6 +42,10 @@ export class Rule extends Lint.Rules.AbstractRule {
 
     public static FAILURE_STRING = "object access via string literals is disallowed";
 
+    public static id(input: string) {
+        return input;
+    }
+
     public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
         return this.applyWithFunction(sourceFile, walk);
     }
@@ -52,8 +56,12 @@ function walk(ctx: Lint.WalkContext<void>) {
         if (isElementAccessExpression(node)) {
             const argument = node.argumentExpression;
             if (argument !== undefined && isStringLiteral(argument) && isValidPropertyAccess(argument.text)) {
-                // for compatibility with typescript@<2.5.0 to avoid fixing expr['__foo'] to expr.___foo
-                const propertyName = ts.unescapeIdentifier(argument.text); // tslint:disable-line:deprecation
+                // typescript@<2.5.0 has an extra underscore in escaped identifier text content,
+                // to avoid fixing issue `expr['__foo'] → expr.___foo`, unescapeIdentifier() is to be used
+                // As of typescript@3, unescapeIdentifier() removed, thus check in runtime, if the method exists
+                // tslint:disable-next-line no-unsafe-any strict-boolean-expressions
+                const unescapeIdentifier: typeof Rule["id"] = (ts as any).unescapeIdentifier || Rule.id;
+                const propertyName = unescapeIdentifier(argument.text);
                 ctx.addFailureAtNode(
                     argument,
                     Rule.FAILURE_STRING,