Enable noImplicitOverride in our codebase

[mjbvz]

--noImplicitOverride

TS 4.3 adds a new strictness option: --noImplicitOverride. This requires that you use the override keyword when overriding and method:

class Foo {
   foo() {...}
}

class SubFoo extends Foo {
    foo() { ... } // ERROR: missing override specifier
}

To fix this, simply add the override keyword:

class SubFoo extends Foo {
    override foo() { ... } 
}

The override keyword does not change runtime behavior but can help programmers in a few ways:

• When reading code, it alerts you that a method is overriding one from the base class

• It is an error to try to override a method that does not exist on the base class. This can help catch errors caused by renaming a method in a base class but forgetting to update the method name in the subclasses.

Enabling

I propose enabling this new flag for both VS Code code and extensions.

Enabling it currently causes ~2200 compile errors, however unlike the previous strictness checks we enabled, I believe should simply use a script to automatically fix the vast majority of them (by inserting override in the necessary location)

[mjbvz]

Here's the simple python script I used to automate most of the rewrites:

from os import path
import re


def fixThisMember(file, line, col):
    with open(file, 'r') as f:
        lines = f.readlines()

    lineContent = lines[line - 1]

    # public? async? method(
    lineContent = re.sub(
        r'^(\s+)((?:public|private|protected) )?(async )?([\w_$]+[\(<])',
        r'\1\2\3override \4',
        lineContent)

    # public? get|set prop(
    lineContent = re.sub(
        r'^(\s+)((?:public|private|protected) )?(get|set) ([\w_$]+)\(',
        r'\1\2override \3 \4(',
        lineContent)

    # public? readonly? prop =
    lineContent = re.sub(
        r'^(\s+)((?:public|private|protected) )?(readonly )?([\w_$]+) =',
        r'\1\2\3override \4 =',
        lineContent)

    # public? readonly? prop:
    lineContent = re.sub(
        r'^(\s+)((?:public|private|protected) )?(readonly )?([\w_$]+):',
        r'\1\2\3override \4:',
        lineContent)

    if lineContent != lines[line - 1]:
        print(file)
        lines[line - 1] = lineContent
        with open(file, 'w') as f:
            f.writelines(lines)


# file containing `yarn watch` error text
with open('override-errors.text') as f:
    for line in f:
        pMatch = re.match(r'.+Error: (.+)\((\d+),(\d+)\): (This member must have an)',
                          line, flags=re.I)
        if pMatch:
            file = pMatch.group(1)
            line = int(pMatch.group(2))
            col = int(pMatch.group(3))
            fixThisMember(file, line, col)

This is a pretty simple script but takes us from 2200 errors to 200 or so.

The remaining errors fall into a few buckets:

• Cases where the property is declared in a constructor.

  Many of these seem to be errors (such as a subclass re-declaring a protected property)

  The rest need to be re-written manually

• declare readonly _serviceBrand: undefined

  Property using declare prompts to add 'override' even though that does not seem valid TypeScript#43566

  We should likely just change these to override readonly _serviceBrand: undefined

• Static properties overriding non-static property

  noImplicitOverride complains about static property not overriding non-static property TypeScript#43563

  Seems to be a bug on the TS side

[Kingwl]

Cool! But... Are there any tools could batch apply quickfix?

[mjbvz]

@Kingwl Not that I know off. For source actions, you can use https://marketplace.visualstudio.com/items?itemName=bierner.folder-source-actions

Hooking up individual quick fixes would be a little more difficult but should be doable (writing a simple python find/replace script was a lot quicker in this case)