Escaped interpolation markers are not unescaped if there are no interpolated expressions in the same text

[timbertson]

• Do you want to request a feature or report a bug?

Bug

• What is the current behavior?

See http://plnkr.co/edit/b5PYWDpsYAoZ5LcDz6o7

• the first div correctly turns the escaped interpolation markers back into {{ ... }}
• the second div doesn't, because there is no interpolation used elsewhere in the element text
• What is the expected behavior?

Escaped interpolation markers should always be unescaped (after interpolation)

• What is the motivation / use case for changing the behavior?

Currently it's impossible to escape {{ ... }} and have it always render correctly (without resorting to hacks like always inserting an empty interpolation at the start of each value).

• Which version of Angular, and which browser and OS does this issue affect? Did this work in previous
  versions of Angular? Please also test with the latest stable and snapshot versions.

I wasn't able to find a nightly link, but looking at the source it hasn't changed recently.

[petebacondarwin]

@timbertson the latest build (of master) is always available at https://code.angularjs.org/snapshot.

[petebacondarwin]

Oh and there is a really interesting previous discussion about all of this here: #5601

[petebacondarwin]

It looks like it is a clearly chosen behaviour. I suspect for performance reasons.
https://github.com/angular/angular.js/blob/master/src/ng/interpolate.js#L197-L202.

The path that fails to unescape these is an optimisation from @jbedard cf83b4f

But he was just reproducing the previous behaviour, which seems that to go back through to 1.3.x

We could do a few things to fix this but I suspect that they would all decrease performance

[gkalpak]

Here's my attempt at a fix #14199.

The downsides:

• It's probably a slight BC (as the previous behavior (even if unintuitive) was documented).
• There is a small performance hit, because we look for escaped markers in all non-empty strings.