cmd/go: examine dependencies of main modules in workspace mode

To make sure that we properly pull in everything in all, because
different main modules can interfere with each others' pruning.

Fixes #49763
Change-Id: I0756993d8ae9919ccb27ec460d579d348c38ec3b
Reviewed-on: https://go-review.googlesource.com/c/go/+/370663
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

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

@@ -386,6 +386,52 @@ func readModGraph(ctx context.Context, pruning modPruning, roots []module.Versio
 	}
 	<-loadQueue.Idle()
 
+	// Reload any dependencies of the main modules which are not
+	// at their selected versions at workspace mode, because the
+	// requirements don't accurately reflect the transitive imports.
+	if pruning == workspace {
+		// hasDepsInAll contains the set of modules that need to be loaded
+		// at workspace pruning because any of their dependencies may
+		// provide packages in all.
+		hasDepsInAll := make(map[string]bool)
+		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
+		// calls enqueue on successively increasing versions of each dependency).
+		for {
+			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 {
+					needsEnqueueing[m] = true
+					continue
+				}
+				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] {
+						needsEnqueueing[s] = true
+					}
+				}
+			}
+			// add all needs enqueueing to paths we care about
+			if len(needsEnqueueing) == 0 {
+				break
+			}
+
+			for p := range needsEnqueueing {
+				enqueue(p, workspace)
+				seen[p] = true
+				hasDepsInAll[p.Path] = true
+			}
+			<-loadQueue.Idle()
+		}
+	}
+
 	if hasError {
 		return mg, mg.findError()
 	}

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

@@ -0,0 +1,176 @@
+# This test makes sure workspace mode's handling of the module graph
+# is compatible with module pruning. The graph we load from either of
+# the workspace modules should be the same, even if their graphs
+# don't overlap.
+#
+# This is the module graph in the test:
+#
+#  example.com/p -> example.com/q v1.0.0
+#  example.com/a -> example.com/b v1.0.0 -> example.com/q v1.1.0 -> example.com/w v1.0.0 -> example.com/x v1.0.0 -> example.com/y v1.0.0
+#                |-> example.com/z v1.0.0                        |-> example.com/z v1.1.0
+#                            |-> example.com/q v1.0.5 -> example.com/r v1.0.0
+# If we didn't load the whole graph and didn't load the dependencies of b
+# when loading p, we would end up loading q v1.0.0, rather than v1.1.0,
+# which is selected by MVS.
+
+go list -m all
+stdout 'example.com/w v1.0.0'
+stdout 'example.com/q v1.1.0'
+stdout 'example.com/z v1.1.0'
+stdout 'example.com/x v1.0.0'
+! stdout 'example.com/r'
+! stdout 'example.com/y'
+
+-- go.work --
+go 1.18
+
+use (
+	./a
+	./p
+)
+
+replace example.com/b v1.0.0 => ./b
+replace example.com/q v1.0.0 => ./q1_0_0
+replace example.com/q v1.0.5 => ./q1_0_5
+replace example.com/q v1.1.0 => ./q1_1_0
+replace example.com/r v1.0.0 => ./r
+replace example.com/w v1.0.0 => ./w
+replace example.com/x v1.0.0 => ./x
+replace example.com/y v1.0.0 => ./y
+replace example.com/z v1.0.0 => ./z1_0_0
+replace example.com/z v1.1.0 => ./z1_1_0
+
+-- a/go.mod --
+module example.com/a
+
+go 1.18
+
+require example.com/b v1.0.0
+require example.com/z v1.0.0
+-- a/foo.go --
+package main
+
+import "example.com/b"
+
+func main() {
+	b.B()
+}
+-- b/go.mod --
+module example.com/b
+
+go 1.18
+
+require example.com/q v1.1.0
+-- b/b.go --
+package b
+
+func B() {
+}
+-- p/go.mod --
+module example.com/p
+
+go 1.18
+
+require example.com/q v1.0.0
+
+replace example.com/q v1.0.0 => ../q1_0_0
+replace example.com/q v1.1.0 => ../q1_1_0
+-- p/main.go --
+package main
+
+import "example.com/q"
+
+func main() {
+	q.PrintVersion()
+}
+-- q1_0_0/go.mod --
+module example.com/q
+
+go 1.18
+-- q1_0_0/q.go --
+package q
+
+import "fmt"
+
+func PrintVersion() {
+	fmt.Println("version 1.0.0")
+}
+-- q1_0_5/go.mod --
+module example.com/q
+
+go 1.18
+
+require example.com/r v1.0.0
+-- q1_0_5/q.go --
+package q
+
+import _ "example.com/r"
+-- q1_1_0/go.mod --
+module example.com/q
+
+require example.com/w v1.0.0
+require example.com/z v1.1.0
+
+go 1.18
+-- q1_1_0/q.go --
+package q
+
+import _ "example.com/w"
+import _ "example.com/z"
+
+import "fmt"
+
+func PrintVersion() {
+	fmt.Println("version 1.1.0")
+}
+-- r/go.mod --
+module example.com/r
+
+go 1.18
+
+require example.com/r v1.0.0
+-- r/r.go --
+package r
+-- w/go.mod --
+module example.com/w
+
+go 1.18
+
+require example.com/x v1.0.0
+-- w/w.go --
+package w
+-- w/w_test.go --
+package w
+
+import _ "example.com/x"
+-- x/go.mod --
+module example.com/x
+
+go 1.18
+-- x/x.go --
+package x
+-- x/x_test.go --
+package x
+import _ "example.com/y"
+-- y/go.mod --
+module example.com/y
+
+go 1.18
+-- y/y.go --
+package y
+-- z1_0_0/go.mod --
+module example.com/z
+
+go 1.18
+
+require example.com/q v1.0.5
+-- z1_0_0/z.go --
+package z
+
+import _ "example.com/q"
+-- z1_1_0/go.mod --
+module example.com/z
+
+go 1.18
+-- z1_1_0/z.go --
+package z