Coffeescript bug: single quoted string with tagged template literal

[greghuc]

Coffeescript bug (parse error)

"civet coffeeCompat"

upperCaseExpr = (textParts, expressions...) ->
  textParts.reduce (text, textPart, i) ->
    text + expressions[i - 1].toUpperCase() + textPart

greet = (_name, _adjective) ->
  upperCaseExpr'A string with no variables'

console.log greet("greg", "awesome")

gives

"civet coffeeCompat"

upperCaseExpr = (textParts, expressions...) ->
  textParts.reduce (text, textPart, i) ->
    text + expressions[i - 1].toUpperCase() + textPart

greet = (_name, _adjective) ->
  upperCaseExpr'A string with no variables'
               ^ ParseError

Playground links

Coffeescript link
Civet link

[greghuc]

Use of tripped quoted string works fine:

"civet coffeeCompat"

upperCaseExpr = (textParts, expressions...) ->
  textParts.reduce (text, textPart, i) ->
    text + expressions[i - 1].toUpperCase() + textPart

greet = (_name, _adjective) ->
  upperCaseExpr"""A string with no variables"""

console.log greet("greg", "awesome")

I believe the underlying issue is that Coffeescript is converting both the single-quoted string and triple-quoted string to a template literal. Civet seems to convert single-quoted to a double-quoted string, and triple-quoted to a template literal.

And a quick check with the Chrome dev tools console shows that the Javascript tagged template literal function only wants a template literal, not a single or double quoted string (grabbing example from MDN):

function tag(strings) {
  console.log(strings.raw[0]);
}

tag`string text line 1 \n string text line 2`;
=> string text line 1 \n string text line 2

tag"string text line 1 \n string text line 2";
=> Uncaught SyntaxError: Unexpected string
tag'string text line 1 \n string text line 2';
=> Uncaught SyntaxError: Unexpected string

[edemaine]

Indeed, 'strings' are currently not able to become template literals, while '''strings''' and """strings""" always are and "strings" are in coffeeCompat mode.

We should be able to fix this, but it will require some more tweaking to separation between string literals and template literals previously considered in #294.

Meanwhile, please use "strings" or '''strings'''.

[STRd6]

@edemaine Do you see any downside to allowing all types of strings to be template literals as a default?

[edemaine]

No, I don't think so, which is why CoffeeScript made this decision. So I was thinking of just adding StringLiteral to the tagged template literal rule, and converting the string to back ticks. (Actually we may need to do this already with CoffeeScript double-quote strings that have no expansions.) Feel free to do this, or I can.

[STRd6]

You can. I'm looking into ||> right now.