Align markdown and orgmode link rendering

[KN4CK3R]

Do we want the orgmode renderer behave like the markdown renderer? I created multiple test cases extracted from the markdown renderer:

    input := `/just/a/path.bin
https://example.com/file.bin
[[file:file.bin][local link]]
[[https://example.com][remote link]]
[[file:image.jpg][local image]]
[[file:path/file.jpg][local image]]
[[file:/path/file.jpg][local image]]
[[file:https://example.com/image.jpg][remote image]]`

    cases := []struct {
        Links    markup.Links
        Expected string
    }{
        { // 0
            Links:  markup.Links{},
            Expected: `<p>/just/a/path.bin<br/>
<a href="https://example.com/file.bin" rel="nofollow">https://example.com/file.bin</a><br/>
<a href="/file.bin" rel="nofollow">local link</a><br/>
<a href="https://example.com" rel="nofollow">remote link</a><br/>
<a href="/image.jpg" target="_blank" rel="nofollow noopener"><img src="/image.jpg" alt="local image"/></a><br/>
<a href="/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/path/file.jpg" alt="local image"/></a><br/>
<a href="/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/path/file.jpg" alt="local image"/></a><br/>
<a href="https://example.com/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://example.com/image.jpg" alt="remote image"/></a></p>`,
        },
        { // 1
            Links:  markup.Links{
                Base:"https://gitea.io/",
            },
            Expected: `<p>/just/a/path.bin<br/>
<a href="https://example.com/file.bin" rel="nofollow">https://example.com/file.bin</a><br/>
<a href="https://gitea.io/file.bin" rel="nofollow">local link</a><br/>
<a href="https://example.com" rel="nofollow">remote link</a><br/>
<a href="https://gitea.io/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://gitea.io/image.jpg" alt="local image"/></a><br/>
<a href="https://gitea.io/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="https://gitea.io/path/file.jpg" alt="local image"/></a><br/>
<a href="https://gitea.io/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="https://gitea.io/path/file.jpg" alt="local image"/></a><br/>
<a href="https://example.com/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://example.com/image.jpg" alt="remote image"/></a></p>`,
        },
        { // 2
            Links:  markup.Links{
                Base: "/relative/path",
            },
            Expected: `<p>/just/a/path.bin<br/>
<a href="https://example.com/file.bin" rel="nofollow">https://example.com/file.bin</a><br/>
<a href="/relative/path/file.bin" rel="nofollow">local link</a><br/>
<a href="https://example.com" rel="nofollow">remote link</a><br/>
<a href="/relative/path/image.jpg" target="_blank" rel="nofollow noopener"><img src="/relative/path/image.jpg" alt="local image"/></a><br/>
<a href="/relative/path/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/relative/path/path/file.jpg" alt="local image"/></a><br/>
<a href="/relative/path/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/relative/path/path/file.jpg" alt="local image"/></a><br/>
<a href="https://example.com/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://example.com/image.jpg" alt="remote image"/></a></p>`,
        },
        { // 3
            Links:  markup.Links{
                Base:       "/user/repo",
                BranchPath: "branch/main",
            },
            Expected: `<p>/just/a/path.bin<br/>
<a href="https://example.com/file.bin" rel="nofollow">https://example.com/file.bin</a><br/>
<a href="/user/repo/src/branch/main/file.bin" rel="nofollow">local link</a><br/>
<a href="https://example.com" rel="nofollow">remote link</a><br/>
<a href="/user/repo/media/branch/main/image.jpg" target="_blank" rel="nofollow noopener"><img src="/user/repo/media/branch/main/image.jpg" alt="local image"/></a><br/>
<a href="/user/repo/media/branch/main/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/user/repo/media/branch/main/path/file.jpg" alt="local image"/></a><br/>
<a href="/user/repo/media/branch/main/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/user/repo/media/branch/main/path/file.jpg" alt="local image"/></a><br/>
<a href="https://example.com/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://example.com/image.jpg" alt="remote image"/></a></p>`,
        },
        { // 4
            Links:  markup.Links{
                Base:     "/relative/path",
                TreePath: "sub/folder",
            },
            Expected: `<p>/just/a/path.bin<br/>
<a href="https://example.com/file.bin" rel="nofollow">https://example.com/file.bin</a><br/>
<a href="/relative/path/file.bin" rel="nofollow">local link</a><br/>
<a href="https://example.com" rel="nofollow">remote link</a><br/>
<a href="/relative/path/image.jpg" target="_blank" rel="nofollow noopener"><img src="/relative/path/image.jpg" alt="local image"/></a><br/>
<a href="/relative/path/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/relative/path/path/file.jpg" alt="local image"/></a><br/>
<a href="/relative/path/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/relative/path/path/file.jpg" alt="local image"/></a><br/>
<a href="https://example.com/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://example.com/image.jpg" alt="remote image"/></a></p>`,
        },
        { // 5
            Links:  markup.Links{
                Base:       "/user/repo",
                BranchPath: "branch/main",
                TreePath:   "sub/folder",
            },
            Expected: `<p>/just/a/path.bin<br/>
<a href="https://example.com/file.bin" rel="nofollow">https://example.com/file.bin</a><br/>
<a href="/user/repo/src/branch/main/sub/folder/file.bin" rel="nofollow">local link</a><br/>
<a href="https://example.com" rel="nofollow">remote link</a><br/>
<a href="/user/repo/media/branch/main/sub/folder/image.jpg" target="_blank" rel="nofollow noopener"><img src="/user/repo/media/branch/main/sub/folder/image.jpg" alt="local image"/></a><br/>
<a href="/user/repo/media/branch/main/sub/folder/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/user/repo/media/branch/main/sub/folder/path/file.jpg" alt="local image"/></a><br/>
<a href="/user/repo/media/branch/main/sub/folder/path/file.jpg" target="_blank" rel="nofollow noopener"><img src="/user/repo/media/branch/main/sub/folder/path/file.jpg" alt="local image"/></a><br/>
<a href="https://example.com/image.jpg" target="_blank" rel="nofollow noopener"><img src="https://example.com/image.jpg" alt="remote image"/></a></p>`,
        },
    }

    for i, c := range cases {
        result, err := RenderString(&markup.RenderContext{Ctx: context.Background(), Links: c.Links}, input)
        assert.NoError(t, err, "Unexpected error in testcase: %v", i)
        assert.Equal(t, c.Expected, result, "Unexpected result in testcase %v", i)
    }

The corresponding markdown input looks like this:

input := `/just/a/path.bin
https://example.com/file.bin
[local link](file.bin)
[remote link](https://example.com)
![local image](image.jpg)
![local image](path/file.jpg)
![local image](/path/file.jpg)
![remote image](https://example.com/image.jpg)`

Things I noticed:

• \n gets rendered as <br/>\n in markdown and just \n in orgmode
• links in markdown get decorated with target and rel attributes.

Originally posted by @KN4CK3R in https://github.com/go-gitea/gitea/issues/29024#issuecomment-1929989609

[silverwind]

Does Orgmode have a spec that shows expected HTML output like CommonMark for Markdown? If so, might be worth to look there. Otherwise I'd lean towards bringing the render output closer together, maybe even so close as to share functions for link generation etc.