Add terminal observer API

[tsmaeder]

What it does

This is a draft PR for feedback on #13085

How to test

The attached theia plugin adds two commands: "Register Observer" and "Remove Observer". The first one allows to register a terminal observer with a given name, regular expression to match and a number of lines to match. The second command unregisters obeservers registered before by name.

The registered observers write the matched strings to the Theia back end log.

Follow-ups

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[tsmaeder]

Here's the plugins

terminalobserver.zip

and here's the source:

terminalobserver.zip

[jonah-iden]

All in all seems to work great and code looks good to me.

just something i found a little weird but i don't know if its a problem. Following console output

gitpod /workspace/theia (13085_terminal_observer) $ testx
bash: testx: command not found
gitpod /workspace/theia (13085_terminal_observer) $ 

having an observer with .*testx.* for one line only prints

["gitpod /workspace/theia (13085_terminal_observer) $ testx                                                                     "]```

But with two lines it prints

["gitpod /workspace/theia (13085_terminal_observer) $ testx                                                                     "]
["bash: testx: command not found                                                                                                "]
["bash: testx: command not found                                                                                                "]

I would have expected for one line it would print the command not found once and for two lines maybe twice because one for when the output is first printed and one when the input prompt is back again or none for 1 line and once for 2 lines

[tsmaeder]

All in all seems to work great and code looks good to me.

just something i found a little weird but i don't know if its a problem. Following console output

gitpod /workspace/theia (13085_terminal_observer) $ testx
bash: testx: command not found
gitpod /workspace/theia (13085_terminal_observer) $ 

having an observer with .*testx.* for one line only prints

["gitpod /workspace/theia (13085_terminal_observer) $ testx                                                                     "]```

But with two lines it prints

["gitpod /workspace/theia (13085_terminal_observer) $ testx                                                                     "]
["bash: testx: command not found                                                                                                "]
["bash: testx: command not found                                                                                                "]

I would have expected for one line it would print the command not found once and for two lines maybe twice because one for when the output is first printed and one when the input prompt is back again or none for 1 line and once for 2 lines

No, I think this is correct: the code is matching against the last n lines each time text is added to the terminal. If you type "testx", the matching will be done basically on every character you type. Since the previous line already matches .*testx.*, the listener will be triggered multiple times as you type.