Seems reasonable. @rintaro, think this would make a good starter bug?

Yeah, this is good StarterBug 🙂

For those who want to tackle this task:
The start point is here https://github.com/apple/swift/blob/6095dc95/lib/Parse/ParseDecl.cpp#L5652 .
Normally, if the current token is colon ':', we parse inheritance clause.

Add another branch like:

if (Tok.is(tok::colon)) {
   ...
} else if (Tok.is(tok::l_paren)) {
  // if the following tokens looks like a type and followed by ')',
  // treat it as Python style inheritance clause.
  // Offer a fix-it to replace '(' with ': ' and remove ')'.
}

Comment by Ryosuke Iwanaga (JIRA)

I'm going to tackle this.

Comment by Kazutaka Homma (JIRA)

riywo (JIRA User) I've been working on this since a few days ago

Comment by Ryosuke Iwanaga (JIRA)

Got it, I gave up.

Comment by Kazutaka Homma (JIRA)

riywo (JIRA User) I think you could work on a task with no assignee.

Comment by Kazutaka Homma (JIRA)

I'm thinking that I should define a new Error message in DiagnosticsParse.def for this specific case. What I came up with so far is the following message.

"expected ':' before inheritance identifier"

However, I'm not sure this is the best. Is there any better idea?

Comment by Kazutaka Homma (JIRA)

Merged

#15010