Fix trim bug with intro/outro

[guybedford]

This fixes a bug where the intro and outro were being removed on trimmed chunks.

This caused issues where magicSting.appendRight('x').trim() would remove the 'x' part.

[lukastaegert]

Well, semantically the original behaviour of magic-string was correct. If you "appendRight" then you tell magic-string that the appended code belongs to the code to the right of the insertion. If there is only whitespace which is removed by "trim" or there is no code at all, then it is correct to remove the appended code.

But then again, I guess this makes things a little easier for rollup. But the new behaviour is inconsistent.

[lukastaegert]

The correct way to add an outro is "appendLeft"

[guybedford]

trim() should behave like String.trim() on the output string. So removing content that would otherwise appear in the output seems blatantly wrong.

That said, the concept of using magicString.overwrite(a, b, '') as a Node removal mechanism does have issues in that it won't remove prepended and appended content.

One thing that might be useful here is a magicString.remove(a, b) which would also remove appended and prepended content along with the removal, unlike overwrite.

Alternatively we could look at an magicstring.overwriteOuter(a, b, '') which would overwrite the content of the range, including any appendages of the range.

[lukastaegert]

I think most of our problems with magic-string are related to the fact that magic-string tries to associate appended and prepended code with neighbouring content and remove it together with this code. Because as far as I know this is virtually NEVER what we want because removed nodes are not rendered at all for performance considerations.
Thus I think what we need is a way to insert code in a way so that it is NOT removed together with neighbouring code and this should solve most of our problems.

[aleclarson]

@lukastaegert I agree with your take in the comment above mine. Perhaps expose a chunk(content) function (not a method) that returns a Chunk instance, and extend the existing methods to support chunks in place of content strings.

// Avoid adding the given content to an `intro` or `outro` of some existing chunk.
magicString.appendLeft(index, chunk(content));

Also, the documentation isn't clear enough about the existing behavior. The concepts of intro and outro are completely foreign to users that don't dive into the implementation.

Perhaps all inserted content should get its own Chunk instance by default (though, that's probably less performant and it's a breaking change). That seems like the most predictable behavior.

@guybedford The overwrite method has a contentOnly option, and the docs suggest that overwrite does remove the intro and outro of a chunk by default. Also, it seems that the remove method also removes the intro and outro.