bug#67809: [PATCH] Add font-locking for assignments in typescript-ts-mode

[Dmitry Gutov <dmitry@gutov.dev>]

On 13/12/2023 21:26, Noah Peart wrote:
> I thought `font-lock-variable-name-face` was standard for assignments?  
> It's what is applied
> in ruby-ts-mode, python-ts-mode, and c-ts-mode for example.  I like it 
> personally, cause
> it allows for visual distinction between l/r values.

ruby and python's parsers cannot distinguish between assignments that 
introduce a new variable (thus working as an implicit declaration) and 
those that reassign an existing variable. Hopefully, we'll be able to 
improve that in the future.

TypeScript, however, has explicit variable declarations.

> Either way, I think the patch can be simplified to only highlight the 
> variable being assigned
> and not any others on the left-hand side.  It would be simpler and more 
> customizable
> to highlight any remaining variables in a `variable` feature in a 
> following rule.

I'm also not sure I agree that, for example, 'arr' is the variable being 
assigned to in the first example. Its value (the reference) doesn't change.

But it's totally fine to add a 'variable' feature to 
typescript-ts-mode's font-lock to apply font-lock-variable-use-face to it.

> I noticed another issue where I forgot to handle `this.var = ` cases as 
> well. I could take
> another stab at it unless there's no interest in this feature.
> 
> On Wed, Dec 13, 2023 at 10:31 AM Dmitry Gutov <dmitry@gutov.dev 
> <mailto:dmitry@gutov.dev>> wrote:
> 
>     Hi!
> 
>     On 13/12/2023 10:33, Noah Peart wrote:
>      >      arr[obj.x * obj.x] = 1;
>      >      //^ font-lock-variable-name-face
>      >      //    ^ font-lock-variable-use-face
>      >      //      ^ font-lock-property-use-face
>      >      obj.x.y = 0;
>      >      //^ font-lock-variable-name-face
>      >      //  ^ font-lock-property-name-face
>      >      //    ^ font-lock-property-name-face
>      >      ++mat[x][arr[0]];
>      >      // ^ font-lock-variable-name-face
>      >      //        ^ font-lock-variable-use-face
> 
>     I think in all of these cases font-lock-variable-name-face should
>     not be
>     used, since arr, and obj, and mat, are all introduced (declared) at a
>     different place.
> 
>     font-lock-variable-use-face is more appropriate.
>