[GitHub] [thrift] pprice opened a new pull request #2462: (typescript): Fix invalid optional members and argument generation

[GitBox <gi...@apache.org>]

pprice opened a new pull request #2462:
URL: https://github.com/apache/thrift/pull/2462


   Fixes two cases where the optional flag `?` is generated incorrectly for typescript, leading to invalid typescript generation that cannot pass `tsc` builds. 
   
   ### 1. Exception types with optional message
   
   It is possible to set an optional message parameter on thrift exception types. 
   
   ```thrift
   exception Bad { 
       1: string message = "";
   }
   ```
   
   However, for the javascript runtime, thrift exception types ultimately derive from `Error` which has a *required* message field. 
   
   **Before**
   ```ts
   export declare class Bad extends Thrift.TException {
       message?: string;
   }
   ```
   Error: TS2416
   ```
   Property 'message' in type 'T' is not assignable to the same property in base type 'Error'.
     Type 'string | undefined' is not assignable to type 'string'.
       Type 'undefined' is not assignable to type 'string'.(2416)
   ```
   
   **After**
   ```ts
   export declare class Bad extends Thrift.TException {
       message: string;
   }
   ```
   
   
   ### Non-optional function arguments after optional arguments
   For service methods it is possible to have non-optional arguments after optional arguments, however this is *not* valid in typescript. 
   
   ```thrift
   service Blah { 
       double getBlah(1: string arg1, 2: string arg2 = "foo", 3: string arg3);
       //                                ~~~~~~~~~~~~~~~~
   }
   ```
   
   **Before**
   ```ts
   export declare class BlahClient {
       getBlah(arg1: string, arg2?: string, arg3: string): Promise<number>;
       //                                   ~~~~~~~~~~~~~~~~
   }
   ```
   Error: TS1016
   ```
   A required parameter cannot follow an optional parameter.
   ```
   
   **After**
   ```ts
   export declare class BlahClient {
       getBlah(arg1: string, arg2?: string, arg3?: string): Promise<number>;
       //                                   ~~~~~~~~~~~~~~
   }
   ```
    


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