Preserve invalid content while formatting

[angelozerr]

When formatting is done with invalid content theinvalid content is lost.

For instance given this XML content:

<a=

After formatting we lose the invalid content =

<a

There are several issues with this problem:

• Bad element formatting is replaced with <null> #1034
• Lone quote inside tag leads to catastrophic formatting #679
• XML format for bad processing instruction removes following element #675
• Disable formatting for next/following lines redhat-developer/vscode-xml#624

and a PR which tries to fix the problem with invalid content inside tag element #766

Today the formatting process load the XML content to format in a DOM Document and the DOM document is visited and we generate the XML content according DOM node type. At the end of the process we return ONE TextEdit which contains the generates XML string.

I think it's not the right way. Indeed after studying the formatting support in the WTP XML Editor (which preserve invalid content), the right way is to create several TextEdits (instead of one textedit) when a format must be done (ex : we create a TextEdit to format a start tag element to indent it, create N TextEdit to format N start tag element to indent them).

See https://github.com/kingargyle/wtp-sourceediting/blob/master/plugins/org.eclipse.wst.xml.core/src/org/eclipse/wst/xml/core/internal/formatter/DefaultXMLPartitionFormatter.java from WTP which uses this strategy.

It's a lot of work, but IMHO I think we should do that to have a clean XML formatter.

[clementnuss]

fully agree with this issue, this is a "killer" for me at the moment, as I have to disable xml formatting altogether for the (many) documents where I use macros that insert credentials in xml fields.
these "macros" are not recognized by lemminx and replaced with null fields instead of being ignored.
commenting here to show the interest and to get notified of future improvements :)

[angelozerr]

This issue should be fixed by the experimental formatter https://github.com/redhat-developer/vscode-xml/blob/master/docs/Formatting.md#xmlformatexperimental