Package import with `go get gonum.org/v1/plot/...` is broken — 404 returned.

首先重现 go get -v gonum.org/v1/plot/...，并检查 https://gonum.org/v1/plot?go-get=1 及其子路径的响应。跟踪 gonum.org 的导入元数据是如何提供的；当元数据请求不再返回 404 且包能够成功导入时，工作就完成了。

I am unable to import this project with go get or dep, which never failed me before.

Call to Parsing meta tags from https://gonum.org/v1/plot?go-get=1 (status code 404) fails.
The page https://www.gonum.org/v1/plot?go-get=1 returns Page not found.

Output:

$ go get -v gonum.org/v1/plot/...

Fetching https://gonum.org/v1/plot?go-get=1
Parsing meta tags from https://gonum.org/v1/plot?go-get=1 (status code 404)
get "gonum.org/v1/plot": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot?go-get=1
gonum.org/v1/plot (download)
Fetching https://gonum.org/v1/plot/vg?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg?go-get=1
get "gonum.org/v1/plot/vg": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot?go-get=1
Parsing meta tags from https://gonum.org/v1/plot?go-get=1 (status code 404)
github.com/golang/freetype (download)
Fetching https://golang.org/x/image/math/fixed?go-get=1
Parsing meta tags from https://golang.org/x/image/math/fixed?go-get=1 (status code 200)
get "golang.org/x/image/math/fixed": found meta tag get.metaImport{Prefix:"golang.org/x/image", VCS:"git", RepoRoot:"https://go.googlesource.com/image"} at https://golang.org/x/image/math/fixed?go-get=1
get "golang.org/x/image/math/fixed": verifying non-authoritative meta tag
Fetching https://golang.org/x/image?go-get=1
Parsing meta tags from https://golang.org/x/image?go-get=1 (status code 200)
golang.org/x/image (download)
Fetching https://golang.org/x/image/font?go-get=1
Parsing meta tags from https://golang.org/x/image/font?go-get=1 (status code 200)
get "golang.org/x/image/font": found meta tag get.metaImport{Prefix:"golang.org/x/image", VCS:"git", RepoRoot:"https://go.googlesource.com/image"} at https://golang.org/x/image/font?go-get=1
get "golang.org/x/image/font": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/vg/fonts?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg/fonts?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg/fonts": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg/fonts?go-get=1
get "gonum.org/v1/plot/vg/fonts": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/vg/draw?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg/draw?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg/draw": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg/draw?go-get=1
get "gonum.org/v1/plot/vg/draw": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/vg/vgeps?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg/vgeps?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg/vgeps": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg/vgeps?go-get=1
get "gonum.org/v1/plot/vg/vgeps": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/vg/vgimg?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg/vgimg?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg/vgimg": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg/vgimg?go-get=1
get "gonum.org/v1/plot/vg/vgimg": verifying non-authoritative meta tag
github.com/llgcode/draw2d (download)
Fetching https://golang.org/x/image/draw?go-get=1
Parsing meta tags from https://golang.org/x/image/draw?go-get=1 (status code 200)
get "golang.org/x/image/draw": found meta tag get.metaImport{Prefix:"golang.org/x/image", VCS:"git", RepoRoot:"https://go.googlesource.com/image"} at https://golang.org/x/image/draw?go-get=1
get "golang.org/x/image/draw": verifying non-authoritative meta tag
Fetching https://golang.org/x/image/math/f64?go-get=1
Parsing meta tags from https://golang.org/x/image/math/f64?go-get=1 (status code 200)
get "golang.org/x/image/math/f64": found meta tag get.metaImport{Prefix:"golang.org/x/image", VCS:"git", RepoRoot:"https://go.googlesource.com/image"} at https://golang.org/x/image/math/f64?go-get=1
get "golang.org/x/image/math/f64": verifying non-authoritative meta tag
Fetching https://golang.org/x/image/tiff?go-get=1
Parsing meta tags from https://golang.org/x/image/tiff?go-get=1 (status code 200)
get "golang.org/x/image/tiff": found meta tag get.metaImport{Prefix:"golang.org/x/image", VCS:"git", RepoRoot:"https://go.googlesource.com/image"} at https://golang.org/x/image/tiff?go-get=1
get "golang.org/x/image/tiff": verifying non-authoritative meta tag
Fetching https://golang.org/x/image/tiff/lzw?go-get=1
Parsing meta tags from https://golang.org/x/image/tiff/lzw?go-get=1 (status code 200)
get "golang.org/x/image/tiff/lzw": found meta tag get.metaImport{Prefix:"golang.org/x/image", VCS:"git", RepoRoot:"https://go.googlesource.com/image"} at https://golang.org/x/image/tiff/lzw?go-get=1
get "golang.org/x/image/tiff/lzw": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/vg/vgpdf?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg/vgpdf?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg/vgpdf": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg/vgpdf?go-get=1
get "gonum.org/v1/plot/vg/vgpdf": verifying non-authoritative meta tag
bitbucket.org/zombiezen/gopdf (download)
go: missing Mercurial command. See https://golang.org/s/gogetcmd
package gonum.org/v1/plot
	imports bitbucket.org/zombiezen/gopdf/pdf: exec: "hg": executable file not found in $PATH
Fetching https://gonum.org/v1/plot/vg/vgsvg?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/vg/vgsvg?go-get=1 (status code 404)
get "gonum.org/v1/plot/vg/vgsvg": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/vg/vgsvg?go-get=1
get "gonum.org/v1/plot/vg/vgsvg": verifying non-authoritative meta tag
github.com/ajstarks/svgo (download)
Fetching https://gonum.org/v1/plot?go-get=1
Parsing meta tags from https://gonum.org/v1/plot?go-get=1 (status code 404)
get "gonum.org/v1/plot": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot?go-get=1
Fetching https://gonum.org/v1/plot/plotter?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/plotter?go-get=1 (status code 404)
get "gonum.org/v1/plot/plotter": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/plotter?go-get=1
get "gonum.org/v1/plot/plotter": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/palette?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/palette?go-get=1 (status code 404)
get "gonum.org/v1/plot/palette": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/palette?go-get=1
get "gonum.org/v1/plot/palette": verifying non-authoritative meta tag
Fetching https://gonum.org/v1/plot/tools/bezier?go-get=1
Parsing meta tags from https://gonum.org/v1/plot/tools/bezier?go-get=1 (status code 404)
get "gonum.org/v1/plot/tools/bezier": found meta tag get.metaImport{Prefix:"gonum.org/v1/plot", VCS:"git", RepoRoot:"https://github.com/gonum/plot"} at https://gonum.org/v1/plot/tools/bezier?go-get=1
get "gonum.org/v1/plot/tools/bezier": verifying non-authoritative meta tag
Fetching https://rsc.io/pdf?go-get=1
Parsing meta tags from https://rsc.io/pdf?go-get=1 (status code 200)
get "rsc.io/pdf": found meta tag get.metaImport{Prefix:"rsc.io/pdf", VCS:"git", RepoRoot:"https://github.com/rsc/pdf"} at https://rsc.io/pdf?go-get=1
rsc.io/pdf (download)