custom java ‘import’ syntax fold, but doesn't work

Refer to @codemirror/lang-java source package implementation. Added my own extension as follows:



             ["ImportDeclaration"]: foldInside,

             BlockComment(tree) { return { from: tree.from + 2, to: - 2 }; }



I recommend you read the docs a bit more, because that is not how things work. You’re defining a facet that’s then never used, and passing it a value that should be used to configure a parser instead. The library doesn’t use global side effects, so you definitely can’t configure anything by just calling some function and then doing nothing with the result. Look into LRLanguage.configure, that’s where props are added to parsers.