CallExpressions to TaggedTemplateLiterals

[boopathi]

• Unsafe Transformation.
• Adds option simplify.callsToTags
• Adds option ecmaVersion (Default = 2015) to preset - now passed only to simplify. Can be used for other transformations later
• Depends on Missing Parens. Syntax Error after transforming ArrowFn as Callee babel#5192

Should we have this in some other plugin ? It can be present anywhere - nothing related to simplify (considering simplify already has too many transformations)

[kangax]

Maybe we should call an option "es2015=true", consistent with es2015 presets in babel, etc.

Other than that, this addition makes sense. I have a feeling it's not very impactful due to gzip, and possibly even worse, but we'd need to see benchmarks for that.

/cc @hzoo

[hzoo]

Yeah I'm not sure about ecmaVersion (I don't know a good name for it either) but I guess we just need to signal that it means that is the minimum supported target version.

Future thoughts: would be better to target a specific feature though (not sure how it would work). An integration with babel-preset-env would be pretty great then since we could pass down the data regarding TaggedTemplate support -> this plugin to turn it on or not.

Kind of like how we do https://github.com/babel/babel-preset-env/blob/master/src/index.js#L210

It really feels like it makes more sense to have something that combined babel-preset-env + babili together and probably with a bundler like webpack..

[boopathi]

Oh. Yeah. I'll change it to use the preset-env data and implement option as target like in babel-preset-env instead of ecmaVersion. This will be useful for many other transformations as well - like we can convert some es5 to es2015 if it is smaller.

[kzc]

Maybe I'm missing something, but is this proposed transform sound?

$ node -e 'function foo(x){console.log(JSON.stringify(x));} foo("bar"); foo`bar`;'
"bar"
["bar"]

$ node -v
v6.9.0

[boopathi]

@kzc Good catch. I forgot about that. Thanks!

Closing this. Will try other ES2015+ transformations with the options discussed above.