@julieqiu

I did some digging into this. It seems that the problem is that blackfriday (markdown rendering engine used by pkgsite) isn't fully compatible with Github-flavoured markdown (GFM).

I can confirm that I wasn't able to (fully) replicate Github's rendering using blackfriday by adding additional format-related flags to https://github.com/golang/pkgsite/blob/master/internal/frontend/overview.go#L143. This seems consistent with the findings in russross/blackfriday#91. In short, their solution to this problem was to create a custom wrapper around blackfriday that is capable of rendering GFM: https://github.com/shurcooL/github_flavored_markdown (note: based on v1 blackfriday, not v2).

Using github_flavored_markdown I was able to render the following readme.

The output seems fairly consistent with https://github.com/Delta456/box-cli-maker/blob/master/README.md. There is no code highlighting for snippets and images are missing (can probably be fixed by writing a custom Walk() function similar to the one for blackfriday - didn't try that at this time due to an incompatible blackfriday version).

I think there are a few options for rendering different markdown flavours on pkg.go.dev:

1. Do something similar to what PyPI is doing (https://packaging.python.org/specifications/core-metadata/#description-content-type-optional) and allow developers to specify the markdown flavour (as a README comment or elsewhere).
2. "Guess" which flavour to use based on internal.ModuleInfo.SourceInfo.RepoURL() or the import path itself (github.com prefix probably makes it reasonable to assume that GFM should be used).
3. I think it is not possible to distinguish between different flavours - files might be valid vanilla markdown and valid GFM, but rendered differently.

Between the two (three) alternatives, I think (2) is the most likely to yield desirable results. Using (1) as an override to (2) might also be an option, but it might cause problems with certain markdown flavours (vanilla markdown doesn't support comments, for example. https://daringfireball.net/projects/markdown/syntax). [EDIT: there's obviosuly another option; use GFM for all readmes].

@akolar I think everyone prefers GFM so we can go with that.

Ignore my last message, false positive (github_flavored_markdown uses blackfriday/v1 which works fine). Markdown syntax has nothing to do with.

The issue is with the blackfriday's parser which can't handle CRLF line terminators. This has been reported several times [1, 2, 3, 4] and there's also a PR (WIP) open [5].

To demonstrate what happens on a simplified readme from the OP (with \r, \r\n and \n used as line endings):

package main

import (
	"fmt"
	"log"
	"os"
	"strings"

	"gopkg.in/russross/blackfriday.v2"
)

const input = `
# Heading

- item 1
- item 2

` + "```go" + `
fmt.Println("string", 123) 
` + "```"

func main() {
	f, err := os.Create("out")
	if err != nil {
		log.Fatalf("failed to open out: %v", err)
	}
	defer f.Close()

	for _, nl := range []string{"\r", "\r\n", "\n"} {
		fmt.Fprintf(f, "Using %s:\n", strings.ReplaceAll(strings.ReplaceAll(nl, "\n", `\n`), "\r", `\r`))

		md := strings.ReplaceAll(input, "\n", nl)
		fmt.Fprintf(f, "-- Input:\n%s\n", md)
		f.WriteString("-- Converted:\n")
		f.Write(blackfriday.Run([]byte(md)))
		f.WriteString("\n\n")
	}
}

Output (with displayed whitespace characters):

Removing \r from sources has fixed the issue for me locally. @julieqiu I'll open a CL in a moment and you can take it from there.

[1] russross/blackfriday#423
[2] russross/blackfriday#575
[3] russross/blackfriday#497
[4] russross/blackfriday#394
[5] russross/blackfriday#428

Unless I'm mistaken, blackfriday isn't actively developed anymore, and many have moved onto goldmark. Hugo, gitea, and even x/tools/present and x/website use goldmark for their markdown support.

Perhaps it'd be better to move to a markdown library which is actively maintained.

Change https://golang.org/cl/243457 mentions this issue: internal: replace \r\n with \n in readmes and licences

https://pkg.go.dev/github.com/Delta456/box-cli-maker?tab=overview

The code highlighted in ' ' and - are still broken.

https://pkg.go.dev/github.com/Delta456/box-cli-maker?tab=overview

The code highlighted in ' ' and - are still broken.

Nvm it got fixed. Thanks again!