Accessibility: NVDA reading wrong or duplicate content in editor

[zersiax]

• VSCode Version: Latest Insider
• OS Version: OS build 15063

Steps to Reproduce:

1. Open a file with code in it, the type does not matter.
2. Arrow through the file at a rate of about twice per second, while NVDA is running.

Observed Behavior:
Rather than speaking the focused line, NVDA will at times read the line or even several lines above it.
Interestingly, braille output appears to work well enough.

Expected Behavior:
NVDA should speak the correct line when navigating through code, for a lot of people using screen readers do not use braille displays to compensate.

Suspected cause:
The fact that braille works well and speech does not leads me to believe it takes too long for the focused line to be visible for NVDA. I don't know enough about the VS Code internals to comment further.

[Neurrone]

I can reproduce this on the latest stable as well with NVDA.

[zersiax]

I have heard from several NVDA users getting hit by this, some going as far as saying this bug renders the IDE impossible to use effectively

[Neurrone]

@zersiax yes, its impossible to use, notepad would be better because of this bug.

Its like having the screen not displaying lines as they properly appear in the file.

[alexdima]

The editor text accessibility is implemented by using a textarea (the same one we use for input events), where we mirror the buffer text and the selection. Until last month (when we updated to a newer Electron version), it was not possible for us to discern if a screen reader is attached or not, so at this point we always do the following:

• the textarea only gets a "page" of the buffer. e.g. if the cursor is in lines 1-10, only lines 1-10 are placed in the textarea. If the cursor is in lines 11-20, only lines 11-20 are placed in the textarea. We are doing this because when opening large files (more than 1 MB), Chromium stalls for seconds if we write large quantities of text to the textarea. This might be a cause of confusion for screen readers when going from line 10 to line 11, for example, where all of a sudden we move to the next page.

• we write to the textarea with the same code path that we paint the lines, i.e. at the next browser animation frame (i.e. not synchronously in the handling of the keyboard event). If two key presses occur before Chromium calls us back it is possible we will update the textarea only once. This might also be a cause of confusion for screen readers.

I will investigate to adopt the new available Electron API to detect when a screen reader is attached and attempt to remove these two possible causes.

[Neurrone]

@alexandrudima thanks. Probably a stupid question, but aren't there standard html controls that can be used for multi-line edits?

[alexdima]

@Neurrone The standard html control that is used for multi-line text is a <textarea>.

[alexdima]

I can confirm and reproduce the problem even in a file with 10 lines (i.e. the "paging" does not appear to be the root cause):

• I create a file with 10 lines, with the content:

Line 1
Line 2
Line 3
Line 4
Line 5
Line 6
Line 7
Line 8
Line 9
Line 10

• I place the cursor at the beginning of the file and I press arrow down 9 times
• Sometimes, the same line is pronounced multiple times by NVDA. e.g. of pronounced text:

Line 1
Line 1
Line 2
Line 3
Line 5
Line 5
Line 6
Line 8
Line 9

I'll try next a change where we call setSelectionRange in the <textarea> synchronously from the keyboard event handler (instead of from the animation frame).

[alexdima]

Unfortunately, calling setSelectionRange synchronously from the keyboard event handler makes no difference.

[alexdima]

Also, this is something I can reproduce on Chrome v58 (via the standalone editor running from master and via the standalone editor from January at https://microsoft.github.io/monaco-editor/)

[Neurrone]

@jcsteh any ideas?