integrate with source maps for good line numbers

[disnet]

It might "just work" with the latest version of escodegen but I have a feeling expansion introduced some problems.

[disnet]

@wycats brought up an interesting idea, to get better line numbers short of the complexity of sourcemaps you can just get smarter about inserting spaces and newlines. For example, a macro that emits a function with line breaks:

macro m {
    case => {
        function foo() {
            return x + 2;
        } 
    }
}
m

could be expanded to:

function foo() { return x + 2; }

This should be easy to do in the expander, just set the lineNumber on each token emitted by a macro expansion to the lineNumber of the invoking macro token (m above).

Going the other way (macro invocation is longer than emitted JS) should be pretty simple:

macro aLongMacroName {
    case => {42}
}
aLongMacroName + 24;

could use loc to expand to:

            42 + 24;

Unfortunately, ASI complicates the process a bit.

macro m {
    case => {
        return
        [1,2,3]
    }
}
m

If we naively expand this while collapsing lines:

return [1,2,3]

we get the wrong result. So the line collapsing needs to be grammar aware (I'm guessing minifiers do the same thing) and insert semicolons at the appropriate points:

return; [1,2,3]

But we still have a problem: return might be a macro. We can't make decisions about the grammar until after full expansion but by then we've lost too much information.

So maybe we can tag each token emitted from a macro with a "potential" collapse line number and do proper semicolon insertion after all macros have been expanded and we have the "real" grammar information?

[krisselden]

is there any more thought on this?

[disnet]

This is happening very soon. I'm expecting sourcemaps to land in the next few weeks.

[disnet]

Initial work checked in with 6c4c40c. Still rough atm but sjs -o outfile.js infile.sjs --sourcemap will create outfile.js.map.

[disnet]

Major fixes for this are in commit 3336448 and PR #127. Unless there are any bugs I don't know about sourcemaps should be usable now.

[disnet]

Should be mostly working with 4f15b50.

[Domiii]

Any documentation on that? Sadly, the wiki entry is still red. :/

[disnet]

Use the --sourcemap flag on sjs. Thanks for pointing out the red wiki link, just made it blue :)