bug#61104: 29.0.60; typescript-ts-mode does not provide compilation-mode support

[Mattias Engdegård]

Jostein, thank you for contributing a new compilation-mode pattern!

We generally want these regexps to be as tight as possible while still doing 
their job. This is partly because the large and ever-growing number of rules 
tend to interfere with one another, and over-broad patterns have shown to be a 
source of performance problems in the past.

I hope you don't mind helping us finishing the job:

First of all, both regexps match arbitrary amounts of horizontal whitespace at 
the beginning of a line, but neither message example you supplied contains any 
such leading whitespace. This means that either the set of test cases needs to 
be extended, or we could safely remove this leading whitespace matcher.

If leading whitespace indeed can occur, then when and how, exactly? Spaces or 
tabs, and how many? Please give us examples from actual compiler output.

Similarly the patterns match arbitrary whitespace before the word "error". This 
seems equally questionable -- would a single space do? If not, please provide 
actual output demonstrating it that could be added to the test suite, and tell 
us how it varies (tabs vs spaces, amount of whitespace, etc).

The following is a minor point that we'll fix but I thought you may want to 
know:

The use of [[:blank:]] and [[:alnum:]] is very likely more expensive than 
required since they accept Unicode whitespace and letters which obviously never 
will occur where matched so if it's all the same to you we'll reduce them to 
ASCII patterns.

Similarly, the inclusion of \r in patterns seems to be a misunderstanding: the 
tail part, "[^\r\n]+$", does not make sense -- normally, carriage returns 
aren't seen in buffers because line terminator translation convert everything 
to a single \n, and if a stray CR did occur then that pattern would never match 
anyway (why?).