code review 4794045: exp/template: A template can be in one set only.

exp/template: A template can be in one set only.
This simplifies the API and makes it easier to make the template
invocation statically secure, at the cost of some minor flexibility.

[r, 2011-07-21 03:35:19]

Hello golang-dev@googlegroups.com,

I'd like you to review this change to
https://go.googlecode.com/hg/

[dsymonds, 2011-07-21 03:39:51]

How does this work for sharing templates across pages? For instance,
many pages might want to share a common header template. Is the way to
do this now to parse the header multiple times and have a disjoint set
per page?


Dave.

[dsymonds, 2011-07-21 03:58:10]

It looks fine in general, though I'm confused by the relationship between a
template and its set. I would have expected the template to know less about its
containing set.

http://codereview.appspot.com/4794045/diff/1/src/pkg/exp/template/doc.go
File src/pkg/exp/template/doc.go (right):

http://codereview.appspot.com/4794045/diff/1/src/pkg/exp/template/doc.go#newc...
src/pkg/exp/template/doc.go:279: parsed template to a set.  A template may be
bound to one set at most.  If it's
s/one set at most/at most one set/?

http://codereview.appspot.com/4794045/diff/1/src/pkg/exp/template/doc.go#newc...
src/pkg/exp/template/doc.go:290: err := set.Execute("T3", os.Stdout, "no data
needed")
fix the arg order: os.Stdout should be first.

http://codereview.appspot.com/4794045/diff/1/src/pkg/exp/template/parse.go
File src/pkg/exp/template/parse.go (right):

http://codereview.appspot.com/4794045/diff/1/src/pkg/exp/template/parse.go#ne...
src/pkg/exp/template/parse.go:569: if t.set != nil {
this removes this template from its set, but I don't understand why. During
parsing, can't you avoid adding it to the set if it fails to parse? And why
would you want to remove it during an execution failure? That might be a
one-time failure.

[r2, 2011-07-21 03:59:23]

Either parse multiple times or just put them in one set. I'd do the latter most
of the time.

This is mostly for security (or enabling it), because it allows us to verify
statically the context in which a template is invoked.

-rob

[r, 2011-07-21 04:16:02]

Hello golang-dev@googlegroups.com, dsymonds@golang.org, r@google.com (cc:
golang-dev@googlegroups.com),

Please take another look.

[r2, 2011-07-21 04:16:08]

good catch; rethought. PTAL

[dsymonds, 2011-07-21 04:20:33]

LGTM

[r, 2011-07-21 04:22:09]

*** Submitted as http://code.google.com/p/go/source/detail?r=1bf4e5073561 ***

exp/template: A template can be in one set only.
This simplifies the API and makes it easier to make the template
invocation statically secure, at the cost of some minor flexibility.

R=golang-dev, dsymonds, r
CC=golang-dev
http://codereview.appspot.com/4794045