[dev.cmdgo] cmd/go: replace Target with MainModules, allowing for multiple targets

This change replaces the Target variable that represents the main module
and the pathPrefix and inGorootSrc which provide other information about
the main module with a single MainModules value that represents multiple
main modules and holds their path prefixes, module roots, and whether
they are in GOROOT/src. In cases where the code checks Target or its
previously associated variables, the code now checks or iterates over
MainModules. In some cases, the code still assumes a single main module
by calling MainModules.MustGetSingleMainModule. Some of those cases are
correct: for instance, there is always only one main module for
mod=vendor. Other cases are accompanied with TODOs and will have to be
fixed in future CLs to properly support multiple main modules.

This CL (and other cls on top of it) are planned to be checked into a
branch to allow for those evaluating the workspaces proposal to try it
hands on.

For #45713

Change-Id: I3b699e1d5cad8c76d62dc567b8460de8c73a87ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/334932
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/src/cmd/go/internal/modload/edit.go b/src/cmd/go/internal/modload/edit.go
index c350b9d1b5..796721c90c 100644
--- a/src/cmd/go/internal/modload/edit.go
+++ b/src/cmd/go/internal/modload/edit.go
@@ -75,7 +75,7 @@ func editRequirements(ctx context.Context, rs *Requirements, tryUpgrade, mustSel
 		// We promote the modules in mustSelect to be explicit requirements.
 		var rootPaths []string
 		for _, m := range mustSelect {
-			if m.Version != "none" && m.Path != Target.Path {
+			if !MainModules.Contains(m.Path) && m.Version != "none" {
 				rootPaths = append(rootPaths, m.Path)
 			}
 		}
@@ -97,7 +97,7 @@ func editRequirements(ctx context.Context, rs *Requirements, tryUpgrade, mustSel
 			}
 		}
 
-		roots, err = mvs.Req(Target, rootPaths, &mvsReqs{roots: mods})
+		roots, err = mvs.Req(MainModules.mustGetSingleMainModule(), rootPaths, &mvsReqs{roots: mods})
 		if err != nil {
 			return nil, false, err
 		}
@@ -218,8 +218,8 @@ func raiseLimitsForUpgrades(ctx context.Context, maxVersion map[string]string, d
 		eagerUpgrades = tryUpgrade
 	} else {
 		for _, m := range tryUpgrade {
-			if m.Path == Target.Path {
-				// Target is already considered to be higher than any possible m, so we
+			if MainModules.Contains(m.Path) {
+				// The main module versions are already considered to be higher than any possible m, so we
 				// won't be upgrading to it anyway and there is no point scanning its
 				// dependencies.
 				continue
@@ -318,7 +318,7 @@ func selectPotentiallyImportedModules(ctx context.Context, limiter *versionLimit
 
 	mods = make([]module.Version, 0, len(limiter.selected))
 	for path, v := range limiter.selected {
-		if v != "none" && path != Target.Path {
+		if v != "none" && !MainModules.Contains(path) {
 			mods = append(mods, module.Version{Path: path, Version: v})
 		}
 	}
@@ -334,7 +334,7 @@ func selectPotentiallyImportedModules(ctx context.Context, limiter *versionLimit
 	}
 	mods = make([]module.Version, 0, len(limiter.selected))
 	for path, _ := range limiter.selected {
-		if path != Target.Path {
+		if !MainModules.Contains(path) {
 			if v := mg.Selected(path); v != "none" {
 				mods = append(mods, module.Version{Path: path, Version: v})
 			}
@@ -415,10 +415,14 @@ func (dq dqState) isDisqualified() bool {
 // itself lazy, its unrestricted dependencies are skipped when scanning
 // requirements.
 func newVersionLimiter(depth modDepth, max map[string]string) *versionLimiter {
+	selected := make(map[string]string)
+	for _, m := range MainModules.Versions() {
+		selected[m.Path] = m.Version
+	}
 	return &versionLimiter{
 		depth:     depth,
 		max:       max,
-		selected:  map[string]string{Target.Path: Target.Version},
+		selected:  selected,
 		dqReason:  map[module.Version]dqState{},
 		requiring: map[module.Version][]module.Version{},
 	}
@@ -492,7 +496,7 @@ func (l *versionLimiter) Select(m module.Version) (conflict module.Version, err
 // as is feasible, we don't want to retain test dependencies that are only
 // marginally relevant at best.
 func (l *versionLimiter) check(m module.Version, depth modDepth) dqState {
-	if m.Version == "none" || m == Target {
+	if m.Version == "none" || m == MainModules.mustGetSingleMainModule() {
 		// version "none" has no requirements, and the dependencies of Target are
 		// tautological.
 		return dqState{}