move compute cache key function to its own function

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

solver/edge.go

@@ -783,19 +783,9 @@ func (e *edge) createInputRequests(desiredState edgeStatusType, f *pipeFactory,
 		} else {
 			debugSchedulerSkipInputRequestBasedOnDepState(e, dep, desiredStateDep)
 		}
+
 		// initialize function to compute cache key based on dependency result
-		if dep.state == edgeStatusComplete && dep.slowCacheReq == nil && (e.slowCacheFunc(dep) != nil || e.preprocessFunc(dep) != nil) && e.cacheMap != nil {
-			pfn := e.preprocessFunc(dep)
-			fn := e.slowCacheFunc(dep)
-			res := dep.result
-			func(pfn PreprocessFunc, fn ResultBasedCacheFunc, res Result, index Index) {
-				dep.slowCacheReq = f.NewFuncRequest(func(ctx context.Context) (interface{}, error) {
-					v, err := e.op.CalcSlowCache(ctx, index, pfn, fn, res)
-					return v, errors.Wrap(err, "failed to compute cache key")
-				})
-			}(pfn, fn, res, dep.index)
-			addedNew = true
-		}
+		addedNew = e.computeCacheKeyFromDep(dep, f) || addedNew
 	}
 	return addedNew
 }
@@ -872,6 +862,26 @@ func (e *edge) createOutgoingRequest(dep *dep, desiredStateDep edgeStatusType, f
 	return true
 }
 
+func (e *edge) computeCacheKeyFromDep(dep *dep, f *pipeFactory) (addedNew bool) {
+	if dep.state != edgeStatusComplete || dep.slowCacheReq != nil || e.cacheMap == nil {
+		return false
+	}
+
+	pfn := e.preprocessFunc(dep)
+	fn := e.slowCacheFunc(dep)
+	if pfn == nil && fn == nil {
+		return false
+	}
+
+	res := dep.result
+	index := dep.index
+	dep.slowCacheReq = f.NewFuncRequest(func(ctx context.Context) (interface{}, error) {
+		v, err := e.op.CalcSlowCache(ctx, index, pfn, fn, res)
+		return v, errors.Wrap(err, "failed to compute cache key")
+	})
+	return true
+}
+
 // execIfPossible creates a request for getting the edge result if there is
 // enough state
 func (e *edge) execIfPossible(f *pipeFactory) bool {