Generated natvis is invalid XML

[Avery3R]

Description

The natvis generator inserts comments before the xml node, which is invalid and causes parsing to fail.

Reproduction steps

• Using VS2022
• Add the generated natvis to your project
• Go to Tools -> Options -> Debugger -> Output Window
• Set Natvis diagnostic messages to verbose
• Attempt to debug project and have natvis work
• json\nlohmann_json.natvis(4,3): Fatal error: Invalid xml declaration. appears in the output window

Opening up the generated natvis in the editor within visual studio shows a red squiggly, hovering over it reveals:

Unexpected XML declaration. The XML declaration must
be the first node in the document and no white space
characters are allowed to appear before it.

Expected vs. actual results

Expected:

generated natvis starts with:

<?xml version="1.0" encoding="utf-8"?>

Reality:

generated natvis starts with:

<!-- * * * * * * * * AUTO-GENERATED FILE  * * * * * * * * -->
<!-- Edit ./tools/generate_natvis/nlohmann_json.natvis.j2 -->
<!-- * * * * * * * * AUTO-GENERATED FILE  * * * * * * * * -->
<?xml version="1.0" encoding="utf-8"?>

Minimal code example

No response

Error messages

`json\nlohmann_json.natvis(4,3): Fatal error: Invalid xml declaration.`

Compiler and operating system

Microsoft Visual Studio Community 2022 Version 17.4.2

Library version

a3e6e26

Validation

• The bug also occurs if the latest version from the develop branch is used.
• I can successfully compile and run the unit tests.

[nlohmann]

You are right - having a comment before the <?xml tag is indeed an error.

[nlohmann]

Can you please try the XML in PR #3863?