cmd/go: avoid re-enqueuing workspace dependencies with errors

Fixes golang#53874.

Change-Id: I41ab15cb9b86b807a9d9ad21fe21fb7aa5fbb46f
Reviewed-on: https://go-review.googlesource.com/c/go/+/417594
Run-TryBot: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

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

@@ -397,7 +397,6 @@ func readModGraph(ctx context.Context, pruning modPruning, roots []module.Versio
 		seen := map[module.Version]bool{}
 		for _, m := range roots {
 			hasDepsInAll[m.Path] = true
-			seen[m] = true
 		}
 		// This loop will terminate because it will call enqueue on each version of
 		// each dependency of the modules in hasDepsInAll at most once (and only
@@ -406,11 +405,11 @@ func readModGraph(ctx context.Context, pruning modPruning, roots []module.Versio
 			needsEnqueueing := map[module.Version]bool{}
 			for p := range hasDepsInAll {
 				m := module.Version{Path: p, Version: mg.g.Selected(p)}
-				reqs, ok := mg.g.RequiredBy(m)
-				if !ok {
+				if !seen[m] {
 					needsEnqueueing[m] = true
 					continue
 				}
+				reqs, _ := mg.g.RequiredBy(m)
 				for _, r := range reqs {
 					s := module.Version{Path: r.Path, Version: mg.g.Selected(r.Path)}
 					if cmpVersion(s.Version, r.Version) > 0 && !seen[s] {

src/cmd/go/testdata/script/work_goproxy_off.txt

@@ -0,0 +1,59 @@
+go work init
+go work use . ./sub
+
+# Verify that the go.mod files for both modules in the workspace are tidy,
+# and add missing go.sum entries as needed.
+
+cp go.mod go.mod.orig
+go mod tidy
+cmp go.mod go.mod.orig
+
+cd sub
+cp go.mod go.mod.orig
+go mod tidy
+cmp go.mod go.mod.orig
+cd ..
+
+go list -m all
+stdout '^rsc\.io/quote v1\.5\.1$'
+stdout '^rsc\.io/sampler v1\.3\.1$'
+
+# Now remove the module dependencies from the module cache.
+# Because one module upgrades a transitive dependency needed by another,
+# listing the modules in the workspace should error out.
+
+go clean -modcache
+env GOPROXY=off
+! go list -m all
+stderr '^go: rsc.io/[email protected]: module lookup disabled by GOPROXY=off$'
+
+-- example.go --
+package example
+
+import _ "rsc.io/sampler"
+-- go.mod --
+module example
+
+go 1.19
+
+require rsc.io/sampler v1.3.0
+
+require (
+	golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
+	rsc.io/testonly v1.0.0 // indirect
+)
+-- sub/go.mod --
+module example/sub
+
+go 1.19
+
+require rsc.io/quote v1.5.1
+
+require (
+	golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
+	rsc.io/sampler v1.3.1 // indirect
+)
+-- sub/sub.go --
+package example
+
+import _ "rsc.io/quote"