markdown: fails to build in module mode because latest version of github.com/russross/blackfriday is v2.0.0+incompatible, which isn't compatible

[julieqiu]

go version

go version go1.12.1 darwin/amd64

go env

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/julie/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/julie/go:/Users/julie/bin:/usr/local/opt/go/libexec"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.12.1/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.12.1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/0_/k0p673rx4r9789jf0pm9425r0000gn/T/go-build590769926=/tmp/go-build -gno-record-gcc-switches -fno-common"

Output of go get -u github.com/shurcooL/markdownfmt

julie@Julies-Air|/tmp/mdtest
) go get -u github.com/shurcooL/markdownfmt

go: finding github.com/shurcooL/markdownfmt latest
go: finding github.com/shurcooL/go/indentwriter latest
go: finding github.com/shurcooL/go latest
go: finding golang.org/x/crypto/ssh/terminal latest
go: finding golang.org/x/crypto/ssh latest
go: finding golang.org/x/crypto latest
# github.com/shurcooL/markdownfmt/markdown
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:136:11: undefined: blackfriday.LIST_TYPE_ORDERED
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:145:11: undefined: blackfriday.LIST_TYPE_ORDERED
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:155:12: undefined: blackfriday.LIST_ITEM_END_OF_LIST
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:188:30: undefined: blackfriday.TABLE_ALIGNMENT_LEFT
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:196:30: undefined: blackfriday.TABLE_ALIGNMENT_RIGHT
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:212:9: undefined: blackfriday.TABLE_ALIGNMENT_LEFT
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:217:9: undefined: blackfriday.TABLE_ALIGNMENT_CENTER
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:226:9: undefined: blackfriday.TABLE_ALIGNMENT_RIGHT
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:467:2: cannot use mr (type *markdownRenderer) as type blackfriday.Renderer in return argument:
	*markdownRenderer does not implement blackfriday.Renderer (missing RenderFooter method)
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:487:21: undefined: blackfriday.EXTENSION_NO_INTRA_EMPHASIS
/Users/julie/go/pkg/mod/github.com/shurcoo!l/[email protected]/markdown/main.go:487:21: too many errors

[dmitshur]

Thanks for reporting.

The problem is that the package github.com/shurcooL/markdownfmt/markdown imports github.com/russross/blackfriday with the intention of getting the blackfriday v1 API. Unfortunately, the blackfriday v2 API made a v2.0.0 tag before modules came out (it was for the purpose of working with gopkg.in), and it results in the "latest" version of github.com/russross/blackfriday according to cmd/go to be v2.0.0+incompatible instead of something that's actually v1, e.g., v1.5.2.

I'm not sure if it's possible for blackfriday to fix the "latest" version of the github.com/russross/blackfriday import path so that it provides the v1 API rather than v2 (which is meant to be available at the github.com/russross/blackfriday/v2 import path). /cc @bcmills

I can fix it in this project by explicitly requiring an older compatible version v1.5.2 of github.com/russross/blackfriday. This issue and the fix are very similar to shurcooL/github_flavored_markdown#22.

[dmitshur]

It turns out I can't use v1.5.2 because it's too old and doesn't include the fix for russross/blackfriday#495, which this project depends on.

[dmitshur]

I'll use the latest pseudo-version of v1 API for now, and open an issue for blackfriday to make a newer v1 release version. Opened russross/blackfriday#533 for that.