Markdown: Breaks italic syntax that contains unescaped underscores

[abemedia]

Prettier 1.17.0
Playground link

--parser markdown

Input:

# Title

## Correct Output

*[Italic link](../_link_including_underscores_.md)*

---

## Incorrect Output

_[Italic link](../_link_including_underscores_.md)_

---  

Output:

# Title

## Correct Output

_[Italic link](../_link_including_underscores_.md)_

---

## Incorrect Output

_[Italic link](../\_link_including_underscores_.md)\_

---

Expected behavior:

# Title

## Correct Output

_[Italic link](../_link_including_underscores_.md)_

---

## Incorrect Output

_[Italic link](../_link_including_underscores_.md)_

---

(Should not escape the final underscore for Incorrect Output.)

[revelt]

Remark parser assumes _[Italic link](../_link_including_underscores_ is emphasis and .md)_ is text. Try yourselves: https://astexplorer.net/ (set markdown as parser)

But shouldn't underscores be escaped anyway?

For example, escaped _[Italic link](../_link_including_underscores\_.md)_ parses correctly.

It seems it's malformed (unescaped) input, not a prettier's bug. What do you think?

[duailibe]

@revelt Thanks again.. you're right.

This isn't a high priority bug since the output is valid, but it's not exactly pretty, so we should probably fix it anyway?

[revelt]

To add 2p, the unescaped input broke even GitHub syntax highlighter, it's visible on a Stylus GitHub Dark theme (v1.21.52):

[josh11b]

I just ran into a problem with this using version 2.3.2:

Input:

_[link 1](https://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming)#Non-subclassable_classes)_
_[link 2](<https://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming)#Non-subclassable_classes>)_

Output:

_[link 1](https://en.wikipedia.org/wiki/Inheritance_(object-oriented*programming)#Non-subclassable_classes)*
_[link 2](<https://en.wikipedia.org/wiki/Inheritance_(object-oriented*programming)#Non-subclassable_classes>)*

This rewrite breaks the link and does not render correctly:

_link 1*
_link 2*

Expected behavior:

_[link 1](<https://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming)#Non-subclassable_classes>)_
_[link 2](<https://en.wikipedia.org/wiki/Inheritance_(object-oriented_programming)#Non-subclassable_classes>)_

which works as expected:
link 1
link 2

[chris-grabcad]

There's a similar issue without even considering links

my_file_name is _italic_

is prettified to

my*file_name is \_italic*

I tried to circumvent this by escaping the _ characters like this

my\_file\_name is _italic_

which gets prettified to

my_file_name is _italic_

which in turn gets prttified to

my*file_name is \_italic*

So it seems that prettifying the file twice (we're using a pre-commit hook with pretty-quick) will break the formatting and the intention

even if you escape the _ at some point it will eventually deteriorate and break syntax :-(

please see this playground

if required I can make this a separate issue.

[seiyab]

Related: #11828