Support ES6 template tags

[BYK]

ES6 has template tags like this:

gettext`Some translatable string with ${variable} replacement`

We'd better support this.

[jacobrask]

Do you have any suggestion on the output of the expressions?

gettext(`Hello ${name}, welcome`)
gettext(`Hello ${name.toUpperCase() + ' ' + lastName.toLowerCase()}, welcome`)
gettext(`Hello ${"Mr" + 'Rask'+getSomething(2)}, welcome`)

Because the expressions can be any valid JavaScript, and we only have the AST, I don't see any way to reproduce the exact contents. The actual AST of the expression is a TemplateExpression node that as far as I can tell can have basically all the available node types as child nodes.

I see the following alternatives:

Only support simple variable expressions

This is the only thing I would personally use, and I already have a working implementation of this. Everything else can be represented by the empty string or some placeholder. The examples above would output

"Hello ${name}, welcome"
"Hello ${}, welcome"
"Hello ${}, welcome"

Generate a representation of the AST

Using escodegen. The examples above would output something like

"Hello ${name}, welcome"
"Hello ${name.toUpperCase() + \" \" + lastName.toLowerCase()}, welcome"
"Hello ${\"Mr\" + \"Rask\" + getSomething(2)}, welcome"

[BYK]

I think for the last two examples we should throw an exception and stop parsing since there's no way to create a reliable representation as you already mentioned. An empty string wouldn't be okay since there may be multiples of these sequences.

Alternatively, we may use numeric indices, or calculate a has from the source code inside the ${} portion and use that as the placeholder name.

[BYK]

@jacobrask still interested in this? This would be great to have in jsxgettext!