text/template: data race in funcs

[bep]

As reported by Go's race detector when building Hugo (https://github.com/spf13/hugo) with go build -race and then using Hugo to build a site:

==================
WARNING: DATA RACE
Write by goroutine 56:
  runtime.mapassign1()
      /home/bep/.gvm/gos/go1.4.2/src/runtime/hashmap.go:383 +0x0
  text/template.addValueFuncs()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/funcs.go:68 +0x4bd
  text/template.(*Template).Funcs()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/template.go:148 +0x253
  html/template.(*escaper).commit()
      /home/bep/.gvm/gos/go1.4.2/src/html/template/escape.go:741 +0x121
  html/template.escapeTemplate()
      /home/bep/.gvm/gos/go1.4.2/src/html/template/escape.go:39 +0x630
  html/template.(*Template).escape()
      /home/bep/.gvm/gos/go1.4.2/src/html/template/template.go:59 +0x1b5
  html/template.(*Template).Execute()
      /home/bep/.gvm/gos/go1.4.2/src/html/template/template.go:75 +0x4d
  github.com/spf13/hugo/hugolib.ShortcodeRender()
      /home/bep/dev/go/src/github.com/spf13/hugo/hugolib/shortcode.go:486 +0xf8
  ...

Previous read by goroutine 58:
  runtime.mapaccess1_faststr()
      /home/bep/.gvm/gos/go1.4.2/src/runtime/hashmap_fast.go:179 +0x0
  text/template.findFunction()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/funcs.go:95 +0x109
  text/template.(*state).evalFunction()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:455 +0x183
  text/template.(*state).evalCommand()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:359 +0x29f
  text/template.(*state).evalPipeline()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:332 +0x207
  text/template.(*state).walk()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:167 +0x194
  text/template.(*state).walk()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:175 +0xa09
  text/template.(*state).walkIfOrWith()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:205 +0x36e
  text/template.(*state).walk()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:172 +0x75c
  text/template.(*state).walk()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:175 +0xa09
  text/template.(*state).walkIfOrWith()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:205 +0x36e
  text/template.(*state).walk()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:172 +0x75c
  text/template.(*state).walk()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:175 +0xa09
  text/template.(*Template).Execute()
      /home/bep/.gvm/gos/go1.4.2/src/text/template/exec.go:155 +0x61d
  html/template.(*Template).Execute()
      /home/bep/.gvm/gos/go1.4.2/src/html/template/template.go:78 +0xd1
 github.com/spf13/hugo/hugolib.ShortcodeRender()
      /home/bep/dev/go/src/github.com/spf13/hugo/hugolib/shortcode.go:486 +0xf8

I have tried my best to rule out the calling code as the source of this race.

[dvyukov]

@robpike

[gopherbot]

CL https://golang.org/cl/10101 mentions this issue.