text/template: allow grouping of pipelines using parentheses
Based on work by Russ Cox. From his CL:
This is generally useful but especially helpful when trying
to use the built-in boolean operators. It lets you write:
{{if not (f 1)}} foo {{end}}
{{if and (f 1) (g 2)}} bar {{end}}
{{if or (f 1) (g 2)}} quux {{end}}
instead of
{{if f 1 | not}} foo {{end}}
{{if f 1}}{{if g 2}} bar {{end}}{{end}}
{{$do := 0}}{{if f 1}}{{$do := 1}}{{else if g 2}}{{$do := 1}}{{end}}{{if $do}} quux {{end}}
The result can be a bit LISPy but the benefit in expressiveness and readability
for such a small change justifies it.
I believe no changes are required to html/template.
Fixes #3276.
R=golang-dev, adg, rogpeppe, minux.ma
CC=golang-dev
https://golang.org/cl/6482056
diff --git a/src/pkg/text/template/parse/parse_test.go b/src/pkg/text/template/parse/parse_test.go
index d7bfc78..da0df20 100644
--- a/src/pkg/text/template/parse/parse_test.go
+++ b/src/pkg/text/template/parse/parse_test.go
@@ -185,6 +185,8 @@
`{{.X | .Y}}`},
{"pipeline with decl", "{{$x := .X|.Y}}", noError,
`{{$x := .X | .Y}}`},
+ {"nested pipeline", "{{.X (.Y .Z) (.A | .B .C) (.E)}}", noError,
+ `{{.X (.Y .Z) (.A | .B .C) (.E)}}`},
{"simple if", "{{if .X}}hello{{end}}", noError,
`{{if .X}}"hello"{{end}}`},
{"if with else", "{{if .X}}true{{else}}false{{end}}", noError,
