Interpolated string literals without interpolation holes do not treat % characters correctly

[abonie]

Because % character can have a special meaning within interpolated strings (as format specifier for interpolation expressions), it needs to be escaped by doubling to be treated as literal % character. However, if an interpolated string literal has no interpolation expressions, it will not drop the extra % chars from content

Repro steps

Create an interpolated string literal without any interpolations (expressions within curly braces) and containing a substring of %%.

Expected behavior

Regardless of whether the literal contained any interpolation expressions, it treats %% as %

> //Interpolated string literal with no interpolation holes
- $"%%";;
val it: string = "%"

> //And for comparison an interpolated string literal *with* interpolation holes
- $"{42=41+1} ... %%";;
val it: string = "True ... %"

Actual behavior

> //Interpolated string literal with no interpolation holes
- $"%%";;
val it: string = "%%"

> //And for comparison an interpolated string literal *with* interpolation holes
- $"{42=41+1} ... %%";;
val it: string = "True ... %"

Known workarounds

Don't use interpolated string literals that have no interpolation holes.

[dsyme]

I think we should consider this a bug fix. Perhaps protected by a version flag in case people ned to revert to the original behaviour.

[dsyme]

(The alternative is to give an error or warning on such strings - perhaps a warning for one version, then an error, then actually make the fix. But either way, it's not intended behaviour and is a bug)