fix(ngPattern): match behaviour of native HTML pattern attribute

[caitp]

From https://html.spec.whatwg.org/multipage/forms.html#attr-input-pattern

The compiled pattern regular expression, when matched against a string, must have its start
anchored to the start of the string and its end anchored to the end of the string.

/CC @matsko please review

Closes #9881

[Narretz]

Do we want breaking changes in 1.3.x?

[caitp]

personally I don't really care, it was wrong before anyway

[caitp]

I don't think we should consider it a breaking change, since it won't break peoples applications.

[gweax]

Well, if an application has a workaround like pattern="^\d{4}$" this change would break it. We could try to guess the people's intentions by checking

    if (regexp[0] !== "^" && regexp[regexp.length - 1] !== "$") 

but I'd say, rather break it completely than break it in only some cases.

[caitp]

Well, if an application has a workaround like pattern="^\d{4}$" this change would break it. We could try to guess the people's intentions by checking

Nope. There's a test in the tree that does exactly this, it's not broken

[gweax]

Yes, you're right. Which means new RegExp("^\\d{4}$") and new RegExp("^^\\d{4}$$")behave in the same way. Weird. I think I'm going to dig into ES5 as to see why.

[caitp]

@petebacondarwin this was supposed to be for the last milestone, guess I forgot to move it there when I wrote this. Can I get you to review since @matsko won't be able to?

[caitp]

@petebacondarwin are you going to look at this and make a call today?

[matsko]

Yes this looks correct. Try entering in "ABCa" into the field.

http://www.w3schools.com/tags/tryit.asp?filename=tryhtml5_input_pattern

It kinda sucks that the form validation API is strict like this.

[petebacondarwin]

I will look in one hour

[petebacondarwin]

LGTM - I am going to add tests that ensure that patterns containing ^ and $ work and then merge.

[petebacondarwin]

Also I will add more documentation explaining the behaviour of pattern as it differs from ngPattern