1695215 - Column Breakpoints gets Added to next line

Status: NEW

(DevTools :: Debugger, defect, P3)

Description

[Jan Honza Odvarko [:Honza] (always need-info? me)]

Originally reported here: https://github.com/firefox-devtools/debugger/issues/7166

So when we add a column breakpoints from a prettified source, it is most likely that it will not add the breakpoint where we want it to.
I did some digging and found that prettyFast is generating correct source map, but the source-map package has a function generatedPositionFor that we use to calculate the generated line and column.
It turns out that this function returns the start of the mapping. e.g.

Generated file:

function e(t){var e=n();return t.replace(e.protocol)}

Original(Pretty) file:

function e(t) {
  var e = n();
  return t.replace(e.protocol)
}

And I ask to get generated position for

location = {
    line: 3,
    column: 12,
}

Then it gives back generated = { line: 1, column: 24, lastColumn: 51 }
Which is the start of the mapping (return t.replace(e.protocol))

Now we have start of mapping, now we need to go to the actual column,

One hacky way that can work is: if we add these things together to work with prettify
location.column - spaces in front of the line + generated.column = 12 - 2 + 24 = 34

I am pretty sure this is not the right way to do it, please let me know what you think.

There is one more point, we use LEAST_UPPER_BOUND bias to search this thing, which returns the greater mapping, so our breakpoints get added to the next line.