[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, 92 insertions, 56 deletions

diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index a3a8021c04..77d2dc4030 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -274,7 +274,9 @@ func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (ma
 
 						// If we're outside of a module, ensure that the failure mode
 						// indicates that.
-						ModRoot()
+						if !HasModRoot() {
+							die()
+						}
 
 						if ld != nil {
 							m.AddError(err)
@@ -306,7 +308,7 @@ func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (ma
 					// The initial roots are the packages in the main module.
 					// loadFromRoots will expand that to "all".
 					m.Errs = m.Errs[:0]
-					matchPackages(ctx, m, opts.Tags, omitStd, []module.Version{Target})
+					matchPackages(ctx, m, opts.Tags, omitStd, MainModules.Versions())
 				} else {
 					// Starting with the packages in the main module,
 					// enumerate the full list of "all".
@@ -443,7 +445,7 @@ func matchLocalDirs(ctx context.Context, m *search.Match, rs *Requirements) {
 		}
 	}
 
-	m.MatchDirs()
+	m.MatchDirs(modRoots)
 }
 
 // resolveLocalPackage resolves a filesystem path to a package path.
@@ -485,49 +487,70 @@ func resolveLocalPackage(ctx context.Context, dir string, rs *Requirements) (str
 		}
 	}
 
-	if modRoot != "" && absDir == modRoot {
-		if absDir == cfg.GOROOTsrc {
-			return "", errPkgIsGorootSrc
+	for _, mod := range MainModules.Versions() {
+		modRoot := MainModules.ModRoot(mod)
+		if modRoot != "" && absDir == modRoot {
+			if absDir == cfg.GOROOTsrc {
+				return "", errPkgIsGorootSrc
+			}
+			return MainModules.PathPrefix(mod), nil
 		}
-		return targetPrefix, nil
 	}
 
 	// Note: The checks for @ here are just to avoid misinterpreting
 	// the module cache directories (formerly GOPATH/src/mod/foo@v1.5.2/bar).
 	// It's not strictly necessary but helpful to keep the checks.
-	if modRoot != "" && strings.HasPrefix(absDir, modRoot+string(filepath.Separator)) && !strings.Contains(absDir[len(modRoot):], "@") {
-		suffix := filepath.ToSlash(absDir[len(modRoot):])
-		if strings.HasPrefix(suffix, "/vendor/") {
-			if cfg.BuildMod != "vendor" {
-				return "", fmt.Errorf("without -mod=vendor, directory %s has no package path", absDir)
+	var pkgNotFoundErr error
+	pkgNotFoundLongestPrefix := ""
+	for _, mainModule := range MainModules.Versions() {
+		modRoot := MainModules.ModRoot(mainModule)
+		if modRoot != "" && strings.HasPrefix(absDir, modRoot+string(filepath.Separator)) && !strings.Contains(absDir[len(modRoot):], "@") {
+			suffix := filepath.ToSlash(absDir[len(modRoot):])
+			if strings.HasPrefix(suffix, "/vendor/") {
+				if cfg.BuildMod != "vendor" {
+					return "", fmt.Errorf("without -mod=vendor, directory %s has no package path", absDir)
+				}
+
+				readVendorList()
+				pkg := strings.TrimPrefix(suffix, "/vendor/")
+				if _, ok := vendorPkgModule[pkg]; !ok {
+					return "", fmt.Errorf("directory %s is not a package listed in vendor/modules.txt", absDir)
+				}
+				return pkg, nil
 			}
 
-			readVendorList()
-			pkg := strings.TrimPrefix(suffix, "/vendor/")
-			if _, ok := vendorPkgModule[pkg]; !ok {
-				return "", fmt.Errorf("directory %s is not a package listed in vendor/modules.txt", absDir)
+			mainModulePrefix := MainModules.PathPrefix(mainModule)
+			if mainModulePrefix == "" {
+				pkg := strings.TrimPrefix(suffix, "/")
+				if pkg == "builtin" {
+					// "builtin" is a pseudo-package with a real source file.
+					// It's not included in "std", so it shouldn't resolve from "."
+					// within module "std" either.
+					return "", errPkgIsBuiltin
+				}
+				return pkg, nil
 			}
-			return pkg, nil
-		}
 
-		if targetPrefix == "" {
-			pkg := strings.TrimPrefix(suffix, "/")
-			if pkg == "builtin" {
-				// "builtin" is a pseudo-package with a real source file.
-				// It's not included in "std", so it shouldn't resolve from "."
-				// within module "std" either.
-				return "", errPkgIsBuiltin
+			pkg := mainModulePrefix + suffix
+			if _, ok, err := dirInModule(pkg, mainModulePrefix, modRoot, true); err != nil {
+				return "", err
+			} else if !ok {
+				// This main module could contain the directory but doesn't. Other main
+				// modules might contain the directory, so wait till we finish the loop
+				// to see if another main module contains directory. But if not,
+				// return an error.
+				if len(mainModulePrefix) > len(pkgNotFoundLongestPrefix) {
+					pkgNotFoundLongestPrefix = mainModulePrefix
+					pkgNotFoundErr = &PackageNotInModuleError{Mod: mainModule, Pattern: pkg}
+
+				}
+				continue
 			}
 			return pkg, nil
 		}
-
-		pkg := targetPrefix + suffix
-		if _, ok, err := dirInModule(pkg, targetPrefix, modRoot, true); err != nil {
-			return "", err
-		} else if !ok {
-			return "", &PackageNotInModuleError{Mod: Target, Pattern: pkg}
-		}
-		return pkg, nil
+	}
+	if pkgNotFoundErr != nil {
+		return "", pkgNotFoundErr
 	}
 
 	if sub := search.InDir(absDir, cfg.GOROOTsrc); sub != "" && sub != "." && !strings.Contains(sub, "@") {
@@ -649,10 +672,10 @@ func ImportFromFiles(ctx context.Context, gofiles []string) {
 }
 
 // DirImportPath returns the effective import path for dir,
-// provided it is within the main module, or else returns ".".
-func DirImportPath(ctx context.Context, dir string) string {
+// provided it is within a main module, or else returns ".".
+func (mms *MainModuleSet) DirImportPath(ctx context.Context, dir string) (path string, m module.Version) {
 	if !HasModRoot() {
-		return "."
+		return ".", module.Version{}
 	}
 	LoadModFile(ctx) // Sets targetPrefix.
 
@@ -662,17 +685,32 @@ func DirImportPath(ctx context.Context, dir string) string {
 		dir = filepath.Clean(dir)
 	}
 
-	if dir == modRoot {
-		return targetPrefix
-	}
-	if strings.HasPrefix(dir, modRoot+string(filepath.Separator)) {
-		suffix := filepath.ToSlash(dir[len(modRoot):])
-		if strings.HasPrefix(suffix, "/vendor/") {
-			return strings.TrimPrefix(suffix, "/vendor/")
+	var longestPrefix string
+	var longestPrefixPath string
+	var longestPrefixVersion module.Version
+	for _, v := range mms.Versions() {
+		modRoot := mms.ModRoot(v)
+		if dir == modRoot {
+			return mms.PathPrefix(v), v
+		}
+		if strings.HasPrefix(dir, modRoot+string(filepath.Separator)) {
+			pathPrefix := MainModules.PathPrefix(v)
+			if pathPrefix > longestPrefix {
+				longestPrefix = pathPrefix
+				longestPrefixVersion = v
+				suffix := filepath.ToSlash(dir[len(modRoot):])
+				if strings.HasPrefix(suffix, "/vendor/") {
+					longestPrefixPath = strings.TrimPrefix(suffix, "/vendor/")
+				}
+				longestPrefixPath = mms.PathPrefix(v) + suffix
+			}
 		}
-		return targetPrefix + suffix
 	}
-	return "."
+	if len(longestPrefix) > 0 {
+		return longestPrefixPath, longestPrefixVersion
+	}
+
+	return ".", module.Version{}
 }
 
 // TargetPackages returns the list of packages in the target (top-level) module
@@ -685,7 +723,7 @@ func TargetPackages(ctx context.Context, pattern string) *search.Match {
 	ModRoot()        // Emits an error if Target cannot contain packages.
 
 	m := search.NewMatch(pattern)
-	matchPackages(ctx, m, imports.AnyTags(), omitStd, []module.Version{Target})
+	matchPackages(ctx, m, imports.AnyTags(), omitStd, MainModules.Versions())
 	return m
 }
 
@@ -931,10 +969,7 @@ func (pkg *loadPkg) fromExternalModule() bool {
 	if pkg.mod.Path == "" {
 		return false // loaded from the standard library, not a module
 	}
-	if pkg.mod.Path == Target.Path {
-		return false // loaded from the main module.
-	}
-	return true
+	return !MainModules.Contains(pkg.mod.Path)
 }
 
 var errMissing = errors.New("cannot find package")
@@ -1205,7 +1240,7 @@ func (ld *loader) updateRequirements(ctx context.Context) (changed bool, err err
 	}
 
 	for _, pkg := range ld.pkgs {
-		if pkg.mod != Target {
+		if pkg.mod.Version != "" || !MainModules.Contains(pkg.mod.Path) {
 			continue
 		}
 		for _, dep := range pkg.imports {
@@ -1462,7 +1497,7 @@ func (ld *loader) applyPkgFlags(ctx context.Context, pkg *loadPkg, flags loadPkg
 		// so it's ok if we call it more than is strictly necessary.
 		wantTest := false
 		switch {
-		case ld.allPatternIsRoot && pkg.mod == Target:
+		case ld.allPatternIsRoot && MainModules.Contains(pkg.mod.Path):
 			// We are loading the "all" pattern, which includes packages imported by
 			// tests in the main module. This package is in the main module, so we
 			// need to identify the imports of its test even if LoadTests is not set.
@@ -1483,7 +1518,7 @@ func (ld *loader) applyPkgFlags(ctx context.Context, pkg *loadPkg, flags loadPkg
 
 		if wantTest {
 			var testFlags loadPkgFlags
-			if pkg.mod == Target || (ld.allClosesOverTests && new.has(pkgInAll)) {
+			if MainModules.Contains(pkg.mod.Path) || (ld.allClosesOverTests && new.has(pkgInAll)) {
 				// Tests of packages in the main module are in "all", in the sense that
 				// they cause the packages they import to also be in "all". So are tests
 				// of packages in "all" if "all" closes over test dependencies.
@@ -1630,7 +1665,7 @@ func (ld *loader) load(ctx context.Context, pkg *loadPkg) {
 	if pkg.dir == "" {
 		return
 	}
-	if pkg.mod == Target {
+	if MainModules.Contains(pkg.mod.Path) {
 		// Go ahead and mark pkg as in "all". This provides the invariant that a
 		// package that is *only* imported by other packages in "all" is always
 		// marked as such before loading its imports.
@@ -1735,13 +1770,14 @@ func (ld *loader) stdVendor(parentPath, path string) string {
 	}
 
 	if str.HasPathPrefix(parentPath, "cmd") {
-		if !ld.VendorModulesInGOROOTSrc || Target.Path != "cmd" {
+		if !ld.VendorModulesInGOROOTSrc || !MainModules.Contains("cmd") {
 			vendorPath := pathpkg.Join("cmd", "vendor", path)
+
 			if _, err := os.Stat(filepath.Join(cfg.GOROOTsrc, filepath.FromSlash(vendorPath))); err == nil {
 				return vendorPath
 			}
 		}
-	} else if !ld.VendorModulesInGOROOTSrc || Target.Path != "std" || str.HasPathPrefix(parentPath, "vendor") {
+	} else if !ld.VendorModulesInGOROOTSrc || !MainModules.Contains("std") || str.HasPathPrefix(parentPath, "vendor") {
 		// If we are outside of the 'std' module, resolve imports from within 'std'
 		// to the vendor directory.
 		//