react-palm
Version:
Elm-like architecture for React apps
105 lines (101 loc) • 3.44 kB
Flow
// Extracted from https://github.com/facebook/react/blob/7bdf93b17a35a5d8fcf0ceae0bf48ed5e6b16688/src/renderers/shared/fiber/ReactFiberTreeReflection.js#L104-L228
function findCurrentFiberUsingSlowPath(fiber) {
const { alternate } = fiber;
if (!alternate) {
return fiber;
}
// If we have two possible branches, we'll walk backwards up to the root
// to see what path the root points to. On the way we may hit one of the
// special cases and we'll deal with them.
let a = fiber;
let b = alternate;
while (true) { // eslint-disable-line
const parentA = a.return;
const parentB = parentA ? parentA.alternate : null;
if (!parentA || !parentB) {
// We're at the root.
break;
}
// If both copies of the parent fiber point to the same child, we can
// assume that the child is current. This happens when we bailout on low
// priority: the bailed out fiber's child reuses the current child.
if (parentA.child === parentB.child) {
let { child } = parentA;
while (child) {
if (child === a) {
// We've determined that A is the current branch.
return fiber;
}
if (child === b) {
// We've determined that B is the current branch.
return alternate;
}
child = child.sibling;
}
// We should never have an alternate for any mounting node. So the only
// way this could possibly happen is if this was unmounted, if at all.
throw new Error('Unable to find node on an unmounted component.');
}
if (a.return !== b.return) {
// The return pointer of A and the return pointer of B point to different
// fibers. We assume that return pointers never criss-cross, so A must
// belong to the child set of A.return, and B must belong to the child
// set of B.return.
a = parentA;
b = parentB;
} else {
// The return pointers point to the same fiber. We'll have to use the
// default, slow path: scan the child sets of each parent alternate to see
// which child belongs to which set.
//
// Search parent A's child set
let didFindChild = false;
let { child } = parentA;
while (child) {
if (child === a) {
didFindChild = true;
a = parentA;
b = parentB;
break;
}
if (child === b) {
didFindChild = true;
b = parentA;
a = parentB;
break;
}
child = child.sibling;
}
if (!didFindChild) {
// Search parent B's child set
({ child } = parentB);
while (child) {
if (child === a) {
didFindChild = true;
a = parentB;
b = parentA;
break;
}
if (child === b) {
didFindChild = true;
b = parentB;
a = parentA;
break;
}
child = child.sibling;
}
if (!didFindChild) {
throw new Error('Child was not found in either parent set. This indicates a bug '
+ 'in React related to the return pointer. Please file an issue.');
}
}
}
}
if (a.stateNode.current === a) {
// We've determined that A is the current branch.
return fiber;
}
// Otherwise B has to be current branch.
return alternate;
}
module.exports = findCurrentFiberUsingSlowPath;