[@types/readable-stream] Fix StringDecoder type usage in readable-stream

[JonathanCallewaert]

StringDecoder is a value, but used as type. This gives an error ('StringDecoder' refers to a value, but is being used as a type here.) when trying to build. Add 'typeof' to fix this

[typescript-bot]

👋 Hi there! I’ve run some quick performance metrics against master and your PR. This is still an experiment, so don’t panic if I say something crazy! I’m still learning how to interpret these metrics.

Let’s review the numbers, shall we?

Comparison details 📊

	master	#37869	diff
Batch compilation
Memory usage (MiB)	67.9	68.1	+0.3%
Type count	9525	9525	0.0%
Assignability cache size	3360	3360	0.0%
Subtype cache size	1	1	0.0%
Identity cache size	7	7	0.0%
Language service
Samples taken	112	112	0.0%
Identifiers in tests	112	112	0.0%
getCompletionsAtPosition
Mean duration (ms)	379.4	367.7	-3.1%
Median duration (ms)	374.5	366.4	-2.2%
Mean CV	13.2%	13.1%	-0.6%
Worst duration (ms)	473.8	425.3	-10.2%
Worst identifier	stream	ANY
getQuickInfoAtPosition
Mean duration (ms)	387.0	393.9	+1.8%
Median duration (ms)	385.6	393.9	+2.2%
Mean CV	13.7%	15.5%	+13.6%
Worst duration (ms)	476.0	456.2	-4.2%
Worst identifier	streamR	RStream

It looks like nothing changed too much. I’m pretty lenient since I’m still an experiment, so take a look anyways and make sure nothing looks out of place.

---

If you have any questions or comments about me, you can ping @andrewbranch. Have a nice day!

[typescript-bot]

@JonathanCA97 Thank you for submitting this PR!

🔔 @TeamworkGuy2 - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[TeamworkGuy2]

This change doesn't work for me locally, here's the auto-complete I get in VS2017 when I change the decoder field type to typeof StringDecoder | null:

Could you post some more details:

• which version of typescript are you using to compile?
• what configuration are you using (your tsconfig.json)?
• what tool or IDE is generating this error and could you post the full error with stack trace from tsc compile command if possible?

[JonathanCallewaert]

Hi, thanks for your answer

• I am using typescript version 3.5.3
• My tsconfig.json looks like this:

  "compilerOptions": {
    "resolveJsonModule": true,
    "module": "commonjs",
    "esModuleInterop": true,
    "target": "es6",
    "noImplicitAny": true,
    "moduleResolution": "node",
    "jsx": "react",
    "outDir": "dist",
    "baseUrl": ".",
    "paths": {
      "*": ["node_modules/*", "src/types/*"]
    },
    "lib": ["es2016", "es2017", "esnext.asynciterable"],
    "sourceMap": false
  },
  "include": ["src/**/*"]
}

• I am using Visual Studio Code. This is the full error I get:

node_modules/@types/readable-stream/index.d.ts:137:18 - error TS2749: 'StringDecoder' refers to a value, but is being used as a type here.

137         decoder: StringDecoder | null;
                     ~~~~~~~~~~~~~


Found 1 error.

npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! orhechestrator@0.1.6 build: `rimraf dist; tsc`
npm ERR! Exit status 2
npm ERR! 
npm ERR! Failed at the orhechestratorl@0.1.6 build script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/jonathan/.npm/_logs/2019-08-24T07_30_58_292Z-debug.log

The node version I use is 10.13.0

[JonathanCallewaert]

If I follow the reference of StringDecoder, I come to this code:

declare module "string_decoder" {
    interface NodeStringDecoder {
        write(buffer: Buffer): string;
        end(buffer?: Buffer): string;
    }
    const StringDecoder: {
        new(encoding?: string): NodeStringDecoder;
    };
}

[TeamworkGuy2]

I'm guessing you're using version ~10.x.x of @types/node in your package.json?

After investigating, I see the following issue between v10 and v12 of string_decoder.d.ts (latest).
To fix the issue, we're going to need to find a way to support both versions.
@types/node@~10.x.x https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/node/v10/string_decoder.d.ts

declare module "string_decoder" {
    interface NodeStringDecoder {
        write(buffer: Buffer): string;
        end(buffer?: Buffer): string;
    }
    const StringDecoder: {
        new(encoding?: string): NodeStringDecoder;
    };
}

@types/node@~12.x.x https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/node/string_decoder.d.ts

declare module "string_decoder" {
    class StringDecoder {
        constructor(encoding?: string);
        write(buffer: Buffer): string;
        end(buffer?: Buffer): string;
    }
}

[JonathanCallewaert]

Using @types/node V12 fixes it indeed, thanks!

[typescript-bot]

After 5 days, no one has reviewed the PR 😞. A maintainer will be reviewing the PR in the next few days and will either merge it or request revisions. Thank you for your patience!