internal/core/adt: simplify recursive getReqSets calls

The call can be skipped entirely if n.dropParentRequirements is true,
given that the result goes entirely unused.

Similarly, a is empty if we don't append from the recursive call,
so move the call to filterNonRecursive inside the conditional too.

While here, set computedCloseInfo to true once we set reqSets.
Resetting the length of reqSets upfront is also unnecessary,
as it's always 0 when we start here.

No visible change to the two benchmarks I'm using for #3881,
but this is still helping clarify that the code is not doing
something else that isn't obvious here, like a side effect.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I321b561ecf56667dcd91fccc351727ca80c093e5
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1217195
Reviewed-by: Marcel van Lohuizen <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: mvdan

internal/core/adt/typocheck.go

@@ -883,19 +883,14 @@ func getReqSets(n *nodeContext) reqSets {
 	if n.computedCloseInfo {
 		return n.reqSets
 	}
-	n.reqSets = n.reqSets[:0]
-	n.computedCloseInfo = true
 
 	a := n.reqSets
 	v := n.node
 
-	if p := v.Parent; p != nil {
-		aReq := getReqSets(p.state)
-		if !n.dropParentRequirements {
-			a = append(a, aReq...)
-		}
+	if p := v.Parent; p != nil && !n.dropParentRequirements {
+		a = append(a, getReqSets(p.state)...)
+		a.filterNonRecursive()
 	}
-	a.filterNonRecursive()
 
 	last := len(a) - 1
 
@@ -972,6 +967,7 @@ outer:
 
 	a.filterTop(n.conjunctInfo, parentConjuncts)
 
+	n.computedCloseInfo = true
 	n.reqSets = a
 	return a
 }