Skip `syntaxFolding` iteration if a fold service returns `false`?

aeaton · August 17, 2022, 6:16pm

I noticed that the foldable function in @codemirror/language will ask the fold service(s) if they know whether a line is foldable, and if the fold services return null it will then iterate through the tree looking for folds with the syntaxFolding function.

github.com

codemirror/language/blob/c5cb3edcc886f1870a225e29cfd5d31798aeec79/src/fold.ts#L56-L62


      
          export function foldable(state: EditorState, lineStart: number, lineEnd: number) {
            for (let service of state.facet(foldService)) {
              let result = service(state, lineStart, lineEnd)
              if (result) return result
            }
            return syntaxFolding(state, lineStart, lineEnd)
          }

To improve performance, if the fold service knows that there definitely isn’t a fold on a given line, would it make sense to allow the fold service to return false and skip the syntaxFolding step?

marijn · August 18, 2022, 9:36am

Is there a concrete performance problem that this would address? If not, I’d rather not complicate this interface.

aeaton · August 30, 2022, 8:07pm

I’m still working on something to reproduce this using vanilla CodeMirror (it may be that it only shows up when the parser is relatively complex, for example), but I’m looking at a reduction from ~10ms in foldable out of a total ~40ms in the event handler to ~1ms in foldable out of a total ~30ms, using if (result === false) return null to avoid wasted searches through the syntax tree.