cmd/go/internal/modload: use atomic.Pointer for Requirements.graph

Change-Id: Ie543e1b1df667cfaf3aafa4be727881461ee8b7d
GitHub-Last-Rev: ed993dbe24
GitHub-Pull-Request: golang/go#54888
Reviewed-on: https://go-review.googlesource.com/c/go/+/428716
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

src/cmd/go/internal/modload/buildlist.go

@@ -73,8 +73,8 @@ type Requirements struct {
 	// nested module back into a parent module).
 	direct map[string]bool
 
-	graphOnce sync.Once    // guards writes to (but not reads from) graph
-	graph     atomic.Value // cachedGraph
+	graphOnce sync.Once // guards writes to (but not reads from) graph
+	graph     atomic.Pointer[cachedGraph]
 }
 
 // A cachedGraph is a non-nil *ModuleGraph, together with any error discovered
@@ -199,7 +199,7 @@ func (rs *Requirements) initVendor(vendorList []module.Version) {
 			mg.g.Require(vendorMod, vendorList)
 		}
 
-		rs.graph.Store(cachedGraph{mg, nil})
+		rs.graph.Store(&cachedGraph{mg, nil})
 	})
 }
 
@@ -240,9 +240,9 @@ func (rs *Requirements) hasRedundantRoot() bool {
 func (rs *Requirements) Graph(ctx context.Context) (*ModuleGraph, error) {
 	rs.graphOnce.Do(func() {
 		mg, mgErr := readModGraph(ctx, rs.pruning, rs.rootModules)
-		rs.graph.Store(cachedGraph{mg, mgErr})
+		rs.graph.Store(&cachedGraph{mg, mgErr})
 	})
-	cached := rs.graph.Load().(cachedGraph)
+	cached := rs.graph.Load()
 	return cached.mg, cached.err
 }
 

src/cmd/go/internal/modload/load.go

@@ -1837,7 +1837,7 @@ func (ld *loader) computePatternAll() (all []string) {
 func (ld *loader) checkMultiplePaths() {
 	mods := ld.requirements.rootModules
 	if cached := ld.requirements.graph.Load(); cached != nil {
-		if mg := cached.(cachedGraph).mg; mg != nil {
+		if mg := cached.mg; mg != nil {
 			mods = mg.BuildList()
 		}
 	}