commit 16c9c007af69bce822e79b0a73d6d51ce9e1e729 (HEAD -> master, tag: swift-DEVELOPMENT-SNAPSHOT-2020-06-13-a)
Merge: 8cb1331c75e 20dbe3fb220
Author: Saleem Abdulrasool <compnerd@compnerd.org>
Date:   Sat Jun 13 08:58:56 2020 -0700

    Merge pull request #&#8203;32350 from compnerd/vim-syntax
    
    vim: improve syntax highlighting rules

Issue Description:

This code crash compiler.

func f(_ a: Int, _ b: Int) {}
f((1, false))

It causes tuple splat fix in matchCallArguments and create locator that is Call > apply argument > arg #​1 to param #​1.
In repairFailures, it attempt to create AllowArgumentMismatch with argument #1.
But there are only one tuple argument, so it take null pointer.

It relates to this:
https://bugs.swift.org/browse/SR-13002

CC: @xedin @LucianoPAlmeida