Modify coverage ranges for code run in VM

[skerit]

• Version: v20.8.1
• Platform: Linux 6.6.4-arch1-1

I run certain code like this:

let head = '(function(module, exports, require, __dirname, __filename, ' + argument_config.names.join(', ') + ') {"use strict";\n';

let exported_function = libvm.runInThisContext(head + source + '\n/**/})', {
	filename: path,
	lineOffset: -1,
});

And contrary to nyc, c8 is able to create coverage for this.
Unfortunately, because of the added header the coverage positions are wrong.

Would it be possible for c8 to use the lineOffset or columnOffset property somehow?

[cenfun]

Try wrapperLength
https://github.com/bcoe/c8/blob/main/index.d.ts#L20

[skerit]

wrapperLength is more like a global setting, not something that you can specify for code run using the vm module.
If being able to dynamically set the wrapper length using comments like /* c8 wrapper-length 47 */ that would be great.
Or just being able to "reset" the column count maybe like /* c8 end wrapper */

[ericmorand]

What is the point, ultimately? Covering the code provided as source?

Also, how would your idea work with your example? You don't know the length of the wrapper at build time:

(function(module, exports, require, __dirname, __filename, ' + argument_config.names.join(', ') + ') {"use strict";\n

The length depend on the argument_config runtime value. What value would you set in the c8 wrapper-length pragma?