Lists with a single empty item (i.e. +, -, *, 1234.) shouldn't be considered Markdown

[dkasak]

Description

When Markdown is turned on, sending a message containing only digits followed
by a period produces a formatted_body containing HTML for an ordered list
with a single empty item.

This seems wrong because a user typing something like 2018.<enter> will
almost never mean "an ordered list with an empty item". Furthermore, it is
related to at least two usability bugs that can look very bad to the end user:

1. Wrong rendering of ordinals with >= 3 digits in Riot Web

   

   This is a separate bug that could (and should) be fixed, but it is also
   particularly bad in combination with this bug, because typing something
   common like 2018. can trigger it.

2. Riot Android renders such messages as empty, as described in Messages containing only digits followed by a period are invisible riot-android#2285.

   They, however, are unsure what to do with it. In a previous Riot Android
   version, it at least rendered the list ordinal correctly even when the list
   item is empty (like Riot Web), but now it has stopped working again.

   I consider this a separate bug too, since empty list items should
   nevertheless get their ordinal rendered.

I propose that messages of form ^[0-9]+\.\s*$ are considered a special case
and not treated as Markdown. This seems to me to follow the principle of least
surprise to the average user. In any case, the Riot clients should all behave
the same.

An example event:

{
"origin_server_ts": 1540893691521,
"sender": "@dkasak:termina.org.uk",
"event_id": "$15408936912708mMjYL:termina.org.uk",
"unsigned": {
    "age": 113,
    "transaction_id": "m1540893692103.11"
},
"content": {
    "body": "2018.",
    "msgtype": "m.text",
    "formatted_body": "<ol start=\"2018\">\n<li></li>\n</ol>\n",
    "format": "org.matrix.custom.html"
},
"type": "m.room.message",
"room_id": "!DCRUrRQxGhHTRwlYla:termina.org.uk"
}

Steps to reproduce

• Ensure Markdown is turned on.
• Type 2018. and press Enter.
• Notice that it has a formatted_body as described above.
• Notice that it renders as an empty message in Riot Android.

I expect this to produce an m.text event without a formatted_body. Instead,
it should only have a body with the contents "2018.".

Version information

• Platform: both web and desktop

For the web app:

• Browser: Firefox 63
• OS: Arch Linux
• URL: riot.im/app

For the desktop app:

• OS: Arch Linux
• Version: 0.17.2

[t3chguy]

Related element-hq/element-web#14621

[NHAS]

I have also run into this bug

[yannicka]

Since this ticket is a duplicate of element-hq/element-web#14621, I think we can close it.

[SimonBrandner]

Closing in favour of element-hq/element-web#14621

[dkasak]

Technically this issue was about the incorrect semantics of messages consisting of only a number and a period (they're treated as lists but they're really not), while element-hq/element-web#14621 is about the cosmetics, so they're not strict duplicates.

[SimonBrandner]

Technically this issue was about the incorrect semantics of messages consisting of only a number and a period (they're treated as lists but they're really not), while element-hq/element-web#14621 is about the cosmetics, so they're not strict duplicates.

While that is true, it is probably fine to keep only one issue. Could you perhaps add some more info from here, if you feel like something there is missing?

[dkasak]

Actually, after some thought, these are really quite separate concerns. element-hq/element-web#14621 is about fixing rendering of HTML messages on the receiving side. This issue is about parsing input differently to not even produce HTML on the sending side. Fixing one does not imply fixing the other.

I'll reopen since I'm planning to submit a PR for this soon, so that I have somewhere to point to.