[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, 18 insertions, 15 deletions

diff --git a/src/cmd/go/internal/search/search.go b/src/cmd/go/internal/search/search.go
index a0c806a259..ebd4990a68 100644
--- a/src/cmd/go/internal/search/search.go
+++ b/src/cmd/go/internal/search/search.go
@@ -202,12 +202,6 @@ func (m *Match) MatchPackages() {
 	}
 }
 
-var modRoot string
-
-func SetModRoot(dir string) {
-	modRoot = dir
-}
-
 // MatchDirs sets m.Dirs to a non-nil slice containing all directories that
 // potentially match a local pattern. The pattern must begin with an absolute
 // path, or "./", or "../". On Windows, the pattern may use slash or backslash
@@ -215,7 +209,7 @@ func SetModRoot(dir string) {
 //
 // If any errors may have caused the set of directories to be incomplete,
 // MatchDirs appends those errors to m.Errs.
-func (m *Match) MatchDirs() {
+func (m *Match) MatchDirs(modRoots []string) {
 	m.Dirs = []string{}
 	if !m.IsLocal() {
 		m.AddError(fmt.Errorf("internal error: MatchDirs: %s is not a valid filesystem pattern", m.pattern))
@@ -253,15 +247,24 @@ func (m *Match) MatchDirs() {
 	// We need to preserve the ./ for pattern matching
 	// and in the returned import paths.
 
-	if modRoot != "" {
+	if len(modRoots) > 1 {
 		abs, err := filepath.Abs(dir)
 		if err != nil {
 			m.AddError(err)
 			return
 		}
-		if !hasFilepathPrefix(abs, modRoot) {
-			m.AddError(fmt.Errorf("directory %s is outside module root (%s)", abs, modRoot))
-			return
+		var found bool
+		for _, modRoot := range modRoots {
+			if modRoot != "" && hasFilepathPrefix(abs, modRoot) {
+				found = true
+			}
+		}
+		if !found {
+			plural := ""
+			if len(modRoots) > 1 {
+				plural = "s"
+			}
+			m.AddError(fmt.Errorf("directory %s is outside module root%s (%s)", abs, plural, strings.Join(modRoots, ", ")))
 		}
 	}
 
@@ -424,19 +427,19 @@ func WarnUnmatched(matches []*Match) {
 
 // ImportPaths returns the matching paths to use for the given command line.
 // It calls ImportPathsQuiet and then WarnUnmatched.
-func ImportPaths(patterns []string) []*Match {
-	matches := ImportPathsQuiet(patterns)
+func ImportPaths(patterns, modRoots []string) []*Match {
+	matches := ImportPathsQuiet(patterns, modRoots)
 	WarnUnmatched(matches)
 	return matches
 }
 
 // ImportPathsQuiet is like ImportPaths but does not warn about patterns with no matches.
-func ImportPathsQuiet(patterns []string) []*Match {
+func ImportPathsQuiet(patterns, modRoots []string) []*Match {
 	var out []*Match
 	for _, a := range CleanPatterns(patterns) {
 		m := NewMatch(a)
 		if m.IsLocal() {
-			m.MatchDirs()
+			m.MatchDirs(modRoots)
 
 			// Change the file import path to a regular import path if the package
 			// is in GOPATH or GOROOT. We don't report errors here; LoadImport