text/template, html/template: document Funcs must be called before Parse

[zwass]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

Go 1.6+

What operating system and processor architecture are you using (go env)?

Any

What did you do?

https://play.golang.org/p/SeHjhOvCFZ (html/template)
https://play.golang.org/p/EeVfv5_IcQ (text/template)

What did you expect to see?

I would expect that both success() and fail() successfully write the string "foo" to stdout

What did you see instead?

The fail function panics with the error, panic: template: :1: function "foo" not defined. If possible, it would feel much more consistent for both of these functions to succeed. If that is not possible, updating the documentation to reflect the need for custom functions to be defined before the template is loaded would be very helpful to confused users.

See, for example:

• http://stackoverflow.com/questions/17570977/template-1-function-copyrightyear-not-defined
• http://stackoverflow.com/questions/17843311/template-and-custom-function-panic-function-not-defined

[gopherbot]

CL https://golang.org/cl/36425 mentions this issue.

[paranoiacblack]

Just adding myself as a reviewer here; I'm not sure how to find the github account of the CL creator.

[odeke-em]

Ping @gulyasm if am not mistaken.

[gulyasm]

@paranoiacblack Yes, it's me.

[gopherbot]

CL https://golang.org/cl/38413 mentions this issue.