In ui.browseableMessage, every other line is empty

[CyrilleB79]

Steps to reproduce:

• Press NVDA+V to ensure screen layout is off.
• On a webpage, press 2 times NVDA+F
• Press many times down arrow
• Press NVDA+V to enable screen layout
• Press up/downArrows again to explore the lines

Actual behavior:

Every other line is empty when screen layout is off.

Expected behavior:

The content should not contain empty lines between useful lines; screen layout should not have any impact here.

NVDA logs, crash dumps and other attachments:

N/A

System configuration

NVDA installed/portable/running from source:

Installed

NVDA version:

Version : source-master-c8a847b (2024.4.0.0)

Windows version:

Windows 10

Name and version of other software in use when reproducing the issue:

N/A

Other information about your system:

N/A

Other questions

Does the issue still occur after restarting your computer?

Not tested, probably yes

Have you tried any other versions of NVDA? If so, please report their behaviors.

2024.3rc1 is OK, i.e. no such issue.

If NVDA add-ons are disabled, is your problem still occurring?

Yes

Does the issue still occur after you run the COM Registration Fixing Tool in NVDA's tools menu?

Not tested, probably unrelated.

Notes

This issue is very likely introduced by #16369. Cc @XLTechie.
Thus #12004 has been reintroduced unfortunately.

[XLTechie]

Unfortunately, there were security concerns about the solution used by #12005 (though I was unaware of #12004, so did not take its solution into account). I will investigate a new solution.

[XLTechie]

A second problem identified while testing for this bug, is that messages formatted with \n sequences, copy without them when the copy button is pressed.

[XLTechie]

I think part of the problem might be in the C code, specifically in NVDAHelper.localLib.VBuf_getLineOffsets.
I might be able to figure out what's going on there (my C is very rusty, but I may remember enough), but at the moment I can't find where the code for that function is. Can anyone with more recent C experience point me to this?
I see that it is exported in nvdaHelper/local/nvdaHelperLocal.def, but that's as much as I have learned.

Probably not an approved use, but maybe I can ask @coderabbitai where the source code for NVDAHelper.localLib.VBuf_getLineOffsets can be found?

[coderabbitai]

Tip

For best results, initiate chat on the files or code changes.

@XLTechie, I've searched through the nvdaHelper directory, but the implementation of VBuf_getLineOffsets wasn't found in the C/C++ source files. It's possible that this function is part of a library linked during the build process or defined in a way not captured by the search (e.g., as a macro or inline function).

You might want to check the build scripts or linked libraries for additional clues. If you have access to the build configuration or any related documentation, that might provide further insights. Let me know if there's anything else I can assist you with!

Analysis chain

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Scripts executed

The following scripts were executed for the analysis:

Script:

#!/bin/bash
# Search for the definition of the VBuf_getLineOffsets function in the C/C++ source files.
ast-grep --lang c --pattern 'VBuf_getLineOffsets($_)' 

Length of output: 55

---

Script:

#!/bin/bash
# Use ripgrep to search for the VBuf_getLineOffsets function in the repository.
rg 'VBuf_getLineOffsets' -A 5

Length of output: 1476

---

Script:

#!/bin/bash
# Search for the VBuf_getLineOffsets function in the C/C++ files within the nvdaHelper directory.
rg 'VBuf_getLineOffsets' nvdaHelper -t c -t cpp -A 5

Length of output: 52

---

Script:

#!/bin/bash
# Search for the VBuf_getLineOffsets function in all files within the nvdaHelper directory.
rg 'VBuf_getLineOffsets' nvdaHelper -A 5

Length of output: 413

[michaelDCurran]

It looks like MSHTML converts line feeds into <br> tags within a <pre> tag. I didn't think this is what a browser was supposed to do. pre tags should have plain text, and no other elements.
Assuming we're not doing anything wrong here in the way we are inserting the message, we might need to change mshtml VBufBackend's fillVBuf to replace br tags with \n assuming we are not already doing that. Right now I'm guessing we are rendering a br tag as a block-level element with a \n inside.
File: nvdaHelper/vbufBackends/mshtml/mshtml.cpp

[XLTechie]

@michaelDCurran regarding your comment above, this only happens to <pre> newlines, while in screen layout off mode. That suggests to me, that it's not the browser's fault.

I tried various changes in the MSHTML VBuf code per your suggestion, but could not figure out where this is handled differently for screen layout off, vs. screen layout on. Regardless, nothing I tried was successful.