[dev.cmdgo] cmd/go: thread through modroots providing replacements

modload.Replacement and modload.resolveReplacement now also return
the modroot of the module providing a replacement so that we can
correctly construct the path of a replaced module (because the
path in the module.Version is relative to the modroot).

For #45713
Change-Id: I8c69ccbcc1f40201071e35fcf93d6b5d0ed4cdf7
Reviewed-on: https://go-review.googlesource.com/c/go/+/334941
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>

9 files changed, 74 insertions, 54 deletions

diff --git a/src/cmd/go/internal/modcmd/vendor.go b/src/cmd/go/internal/modcmd/vendor.go
index 6273afbbe6..774fc3052f 100644
--- a/src/cmd/go/internal/modcmd/vendor.go
+++ b/src/cmd/go/internal/modcmd/vendor.go
@@ -128,7 +128,8 @@ func runVendor(ctx context.Context, cmd *base.Command, args []string) {
 	}
 
 	for _, m := range vendorMods {
-		line := moduleLine(m, modload.Replacement(m))
+		replacement, _ := modload.Replacement(m)
+		line := moduleLine(m, replacement)
 		io.WriteString(w, line)
 
 		goVersion := ""
diff --git a/src/cmd/go/internal/modget/get.go b/src/cmd/go/internal/modget/get.go
index 3c8b5a7090..6eae44f1a4 100644
--- a/src/cmd/go/internal/modget/get.go
+++ b/src/cmd/go/internal/modget/get.go
@@ -1615,7 +1615,7 @@ func (r *resolver) checkPackageProblems(ctx context.Context, pkgPatterns []strin
 		i := i
 		m := r.buildList[i]
 		mActual := m
-		if mRepl := modload.Replacement(m); mRepl.Path != "" {
+		if mRepl, _ := modload.Replacement(m); mRepl.Path != "" {
 			mActual = mRepl
 		}
 		old := module.Version{Path: m.Path, Version: r.initialVersion[m.Path]}
@@ -1623,7 +1623,7 @@ func (r *resolver) checkPackageProblems(ctx context.Context, pkgPatterns []strin
 			continue
 		}
 		oldActual := old
-		if oldRepl := modload.Replacement(old); oldRepl.Path != "" {
+		if oldRepl, _ := modload.Replacement(old); oldRepl.Path != "" {
 			oldActual = oldRepl
 		}
 		if mActual == oldActual || mActual.Version == "" || !modfetch.HaveSum(oldActual) {
diff --git a/src/cmd/go/internal/modload/build.go b/src/cmd/go/internal/modload/build.go
index a5c5ad9b44..2973586479 100644
--- a/src/cmd/go/internal/modload/build.go
+++ b/src/cmd/go/internal/modload/build.go
@@ -241,7 +241,7 @@ func moduleInfo(ctx context.Context, rs *Requirements, m module.Version, mode Li
 	}
 
 	// completeFromModCache fills in the extra fields in m using the module cache.
-	completeFromModCache := func(m *modinfo.ModulePublic) {
+	completeFromModCache := func(m *modinfo.ModulePublic, replacedFrom string) {
 		checksumOk := func(suffix string) bool {
 			return rs == nil || m.Version == "" || cfg.BuildMod == "mod" ||
 				modfetch.HaveSum(module.Version{Path: m.Path, Version: m.Version + suffix})
@@ -260,7 +260,7 @@ func moduleInfo(ctx context.Context, rs *Requirements, m module.Version, mode Li
 		if m.GoVersion == "" && checksumOk("/go.mod") {
 			// Load the go.mod file to determine the Go version, since it hasn't
 			// already been populated from rawGoVersion.
-			if summary, err := rawGoModSummary(mod); err == nil && summary.goVersion != "" {
+			if summary, err := rawGoModSummary(mod, replacedFrom); err == nil && summary.goVersion != "" {
 				m.GoVersion = summary.goVersion
 			}
 		}
@@ -290,11 +290,11 @@ func moduleInfo(ctx context.Context, rs *Requirements, m module.Version, mode Li
 	if rs == nil {
 		// If this was an explicitly-versioned argument to 'go mod download' or
 		// 'go list -m', report the actual requested version, not its replacement.
-		completeFromModCache(info) // Will set m.Error in vendor mode.
+		completeFromModCache(info, "") // Will set m.Error in vendor mode.
 		return info
 	}
 
-	r := Replacement(m)
+	r, replacedFrom := Replacement(m)
 	if r.Path == "" {
 		if cfg.BuildMod == "vendor" {
 			// It's tempting to fill in the "Dir" field to point within the vendor
@@ -303,7 +303,7 @@ func moduleInfo(ctx context.Context, rs *Requirements, m module.Version, mode Li
 			// interleave packages from different modules if one module path is a
 			// prefix of the other.
 		} else {
-			completeFromModCache(info)
+			completeFromModCache(info, "")
 		}
 		return info
 	}
@@ -328,7 +328,7 @@ func moduleInfo(ctx context.Context, rs *Requirements, m module.Version, mode Li
 		info.Replace.GoMod = filepath.Join(info.Replace.Dir, "go.mod")
 	}
 	if cfg.BuildMod != "vendor" {
-		completeFromModCache(info.Replace)
+		completeFromModCache(info.Replace, replacedFrom)
 		info.Dir = info.Replace.Dir
 		info.GoMod = info.Replace.GoMod
 		info.Retracted = info.Replace.Retracted
@@ -368,7 +368,7 @@ func PackageBuildInfo(path string, deps []string) string {
 			mv = "(devel)"
 		}
 		fmt.Fprintf(&buf, "%s\t%s\t%s", token, m.Path, mv)
-		if r := Replacement(m); r.Path == "" {
+		if r, _ := Replacement(m); r.Path == "" {
 			fmt.Fprintf(&buf, "\t%s\n", modfetch.Sum(m))
 		} else {
 			fmt.Fprintf(&buf, "\n=>\t%s\t%s\t%s\n", r.Path, r.Version, modfetch.Sum(r))
diff --git a/src/cmd/go/internal/modload/import.go b/src/cmd/go/internal/modload/import.go
index 088d0c14ec..5741299281 100644
--- a/src/cmd/go/internal/modload/import.go
+++ b/src/cmd/go/internal/modload/import.go
@@ -479,11 +479,12 @@ func queryImport(ctx context.Context, path string, rs *Requirements) (module.Ver
 		// The package path is not valid to fetch remotely,
 		// so it can only exist in a replaced module,
 		// and we know from the above loop that it is not.
+		replacement, _ := Replacement(mods[0])
 		return module.Version{}, &PackageNotInModuleError{
 			Mod:         mods[0],
 			Query:       "latest",
 			Pattern:     path,
-			Replacement: Replacement(mods[0]),
+			Replacement: replacement,
 		}
 	}
 
@@ -652,7 +653,7 @@ func fetch(ctx context.Context, mod module.Version, needSum bool) (dir string, i
 	if modRoot := MainModules.ModRoot(mod); modRoot != "" {
 		return modRoot, true, nil
 	}
-	if r := Replacement(mod); r.Path != "" {
+	if r, _ := Replacement(mod); r.Path != "" {
 		if r.Version == "" {
 			dir = r.Path
 			if !filepath.IsAbs(dir) {
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index 18b07cb125..de8adbafc4 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -1475,7 +1475,8 @@ func keepSums(ctx context.Context, ld *loader, rs *Requirements, which whichSums
 					for prefix := pkg.path; prefix != "."; prefix = path.Dir(prefix) {
 						if v, ok := rs.rootSelected(prefix); ok && v != "none" {
 							m := module.Version{Path: prefix, Version: v}
-							keep[resolveReplacement(m)] = true
+							r, _ := resolveReplacement(m)
+							keep[r] = true
 						}
 					}
 					continue
@@ -1486,7 +1487,8 @@ func keepSums(ctx context.Context, ld *loader, rs *Requirements, which whichSums
 			for prefix := pkg.path; prefix != "."; prefix = path.Dir(prefix) {
 				if v := mg.Selected(prefix); v != "none" {
 					m := module.Version{Path: prefix, Version: v}
-					keep[resolveReplacement(m)] = true
+					r, _ := resolveReplacement(m)
+					keep[r] = true
 				}
 			}
 		}
@@ -1498,7 +1500,7 @@ func keepSums(ctx context.Context, ld *loader, rs *Requirements, which whichSums
 		// Save sums for the root modules (or their replacements), but don't
 		// incur the cost of loading the graph just to find and retain the sums.
 		for _, m := range rs.rootModules {
-			r := resolveReplacement(m)
+			r, _ := resolveReplacement(m)
 			keep[modkey(r)] = true
 			if which == addBuildListZipSums {
 				keep[r] = true
@@ -1511,13 +1513,15 @@ func keepSums(ctx context.Context, ld *loader, rs *Requirements, which whichSums
 				// The requirements from m's go.mod file are present in the module graph,
 				// so they are relevant to the MVS result regardless of whether m was
 				// actually selected.
-				keep[modkey(resolveReplacement(m))] = true
+				r, _ := resolveReplacement(m)
+				keep[modkey(r)] = true
 			}
 		})
 
 		if which == addBuildListZipSums {
 			for _, m := range mg.BuildList() {
-				keep[resolveReplacement(m)] = true
+				r, _ := resolveReplacement(m)
+				keep[r] = true
 			}
 		}
 	}
diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index 7def3c2625..dd69e2afbf 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -582,7 +582,7 @@ func pathInModuleCache(ctx context.Context, dir string, rs *Requirements) string
 	tryMod := func(m module.Version) (string, bool) {
 		var root string
 		var err error
-		if repl := Replacement(m); repl.Path != "" && repl.Version == "" {
+		if repl, _ := Replacement(m); repl.Path != "" && repl.Version == "" {
 			root = repl.Path
 			if !filepath.IsAbs(root) {
 				root = filepath.Join(ModRoot(), root)
@@ -1800,7 +1800,7 @@ func (ld *loader) checkMultiplePaths() {
 
 	firstPath := map[module.Version]string{}
 	for _, mod := range mods {
-		src := resolveReplacement(mod)
+		src, _ := resolveReplacement(mod)
 		if prev, ok := firstPath[src]; !ok {
 			firstPath[src] = mod.Path
 		} else if prev != mod.Path {
diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index 31e79a3646..bc5c83dffc 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -171,7 +171,7 @@ func CheckRetractions(ctx context.Context, m module.Version) (err error) {
 		// Cannot be retracted.
 		return nil
 	}
-	if repl := Replacement(module.Version{Path: m.Path}); repl.Path != "" {
+	if repl, _ := Replacement(module.Version{Path: m.Path}); repl.Path != "" {
 		// All versions of the module were replaced.
 		// Don't load retractions, since we'd just load the replacement.
 		return nil
@@ -188,11 +188,11 @@ func CheckRetractions(ctx context.Context, m module.Version) (err error) {
 	// We load the raw file here: the go.mod file may have a different module
 	// path that we expect if the module or its repository was renamed.
 	// We still want to apply retractions to other aliases of the module.
-	rm, err := queryLatestVersionIgnoringRetractions(ctx, m.Path)
+	rm, replacedFrom, err := queryLatestVersionIgnoringRetractions(ctx, m.Path)
 	if err != nil {
 		return err
 	}
-	summary, err := rawGoModSummary(rm)
+	summary, err := rawGoModSummary(rm, replacedFrom)
 	if err != nil {
 		return err
 	}
@@ -290,17 +290,17 @@ func CheckDeprecation(ctx context.Context, m module.Version) (deprecation string
 		// Don't look up deprecation.
 		return "", nil
 	}
-	if repl := Replacement(module.Version{Path: m.Path}); repl.Path != "" {
+	if repl, _ := Replacement(module.Version{Path: m.Path}); repl.Path != "" {
 		// All versions of the module were replaced.
 		// We'll look up deprecation separately for the replacement.
 		return "", nil
 	}
 
-	latest, err := queryLatestVersionIgnoringRetractions(ctx, m.Path)
+	latest, replacedFrom, err := queryLatestVersionIgnoringRetractions(ctx, m.Path)
 	if err != nil {
 		return "", err
 	}
-	summary, err := rawGoModSummary(latest)
+	summary, err := rawGoModSummary(latest, replacedFrom)
 	if err != nil {
 		return "", err
 	}
@@ -317,10 +317,11 @@ func replacement(mod module.Version, index *modFileIndex) (fromVersion string, t
 	return "", module.Version{}, false
 }
 
-// Replacement returns the replacement for mod, if any, from go.mod.
+// Replacement returns the replacement for mod, if any, and and the module root
+// directory of the main module containing the replace directive.
 // If there is no replacement for mod, Replacement returns
 // a module.Version with Path == "".
-func Replacement(mod module.Version) module.Version {
+func Replacement(mod module.Version) (module.Version, string) {
 	_ = TODOWorkspaces("support replaces in the go.work file")
 	foundFrom, found, foundModRoot := "", module.Version{}, ""
 	for _, v := range MainModules.Versions() {
@@ -331,22 +332,24 @@ func Replacement(mod module.Version) module.Version {
 					_ = TODOWorkspaces("once the go.work file supports replaces, recommend them as a way to override conflicts")
 					base.Errorf("conflicting replacements found for %v in workspace modules defined by %v and %v",
 						mod, modFilePath(foundModRoot), modFilePath(modRoot))
-					return found
+					return found, foundModRoot
 				}
 				found, foundModRoot = r, modRoot
 			}
 		}
 	}
-	return found
+	return found, foundModRoot
 }
 
 // resolveReplacement returns the module actually used to load the source code
 // for m: either m itself, or the replacement for m (iff m is replaced).
-func resolveReplacement(m module.Version) module.Version {
-	if r := Replacement(m); r.Path != "" {
-		return r
+// It also returns the modroot of the module providing the replacement if
+// one was found.
+func resolveReplacement(m module.Version) (module.Version, string) {
+	if r, replacedFrom := Replacement(m); r.Path != "" {
+		return r, replacedFrom
 	}
-	return m
+	return m, ""
 }
 
 // indexModFile rebuilds the index of modFile.
@@ -533,7 +536,7 @@ func goModSummary(m module.Version) (*modFileSummary, error) {
 		return summary, nil
 	}
 
-	actual := resolveReplacement(m)
+	actual, replacedFrom := resolveReplacement(m)
 	if HasModRoot() && cfg.BuildMod == "readonly" && !inWorkspaceMode() && actual.Version != "" {
 		key := module.Version{Path: actual.Path, Version: actual.Version + "/go.mod"}
 		if !modfetch.HaveSum(key) {
@@ -541,7 +544,7 @@ func goModSummary(m module.Version) (*modFileSummary, error) {
 			return nil, module.VersionError(actual, &sumMissingError{suggestion: suggestion})
 		}
 	}
-	summary, err := rawGoModSummary(actual)
+	summary, err := rawGoModSummary(actual, replacedFrom)
 	if err != nil {
 		return nil, err
 	}
@@ -605,18 +608,23 @@ func goModSummary(m module.Version) (*modFileSummary, error) {
 // its dependencies.
 //
 // rawGoModSummary cannot be used on the Target module.
-func rawGoModSummary(m module.Version) (*modFileSummary, error) {
+
+func rawGoModSummary(m module.Version, replacedFrom string) (*modFileSummary, error) {
 	if m.Path == "" && MainModules.Contains(m.Path) {
 		panic("internal error: rawGoModSummary called on the Target module")
 	}
 
+	type key struct {
+		m            module.Version
+		replacedFrom string
+	}
 	type cached struct {
 		summary *modFileSummary
 		err     error
 	}
-	c := rawGoModSummaryCache.Do(m, func() interface{} {
+	c := rawGoModSummaryCache.Do(key{m, replacedFrom}, func() interface{} {
 		summary := new(modFileSummary)
-		name, data, err := rawGoModData(m)
+		name, data, err := rawGoModData(m, replacedFrom)
 		if err != nil {
 			return cached{nil, err}
 		}
@@ -666,12 +674,15 @@ var rawGoModSummaryCache par.Cache // module.Version → rawGoModSummary result
 //
 // Unlike rawGoModSummary, rawGoModData does not cache its results in memory.
 // Use rawGoModSummary instead unless you specifically need these bytes.
-func rawGoModData(m module.Version) (name string, data []byte, err error) {
+func rawGoModData(m module.Version, replacedFrom string) (name string, data []byte, err error) {
 	if m.Version == "" {
 		// m is a replacement module with only a file path.
 		dir := m.Path
 		if !filepath.IsAbs(dir) {
-			dir = filepath.Join(ModRoot(), dir)
+			if replacedFrom == "" {
+				panic(fmt.Errorf("missing module root of main module providing replacement with relative path: %v", dir))
+			}
+			dir = filepath.Join(replacedFrom, dir)
 		}
 		name = filepath.Join(dir, "go.mod")
 		if gomodActual, ok := fsys.OverlayPath(name); ok {
@@ -706,19 +717,20 @@ func rawGoModData(m module.Version) (name string, data []byte, err error) {
 //
 // If the queried latest version is replaced,
 // queryLatestVersionIgnoringRetractions returns the replacement.
-func queryLatestVersionIgnoringRetractions(ctx context.Context, path string) (latest module.Version, err error) {
+func queryLatestVersionIgnoringRetractions(ctx context.Context, path string) (latest module.Version, replacedFrom string, err error) {
 	type entry struct {
-		latest module.Version
-		err    error
+		latest       module.Version
+		replacedFrom string // if latest is a replacement
+		err          error
 	}
 	e := latestVersionIgnoringRetractionsCache.Do(path, func() interface{} {
 		ctx, span := trace.StartSpan(ctx, "queryLatestVersionIgnoringRetractions "+path)
 		defer span.Done()
 
-		if repl := Replacement(module.Version{Path: path}); repl.Path != "" {
+		if repl, replFrom := Replacement(module.Version{Path: path}); repl.Path != "" {
 			// All versions of the module were replaced.
 			// No need to query.
-			return &entry{latest: repl}
+			return &entry{latest: repl, replacedFrom: replFrom}
 		}
 
 		// Find the latest version of the module.
@@ -730,12 +742,12 @@ func queryLatestVersionIgnoringRetractions(ctx context.Context, path string) (la
 			return &entry{err: err}
 		}
 		latest := module.Version{Path: path, Version: rev.Version}
-		if repl := resolveReplacement(latest); repl.Path != "" {
-			latest = repl
+		if repl, replFrom := resolveReplacement(latest); repl.Path != "" {
+			latest, replacedFrom = repl, replFrom
 		}
-		return &entry{latest: latest}
+		return &entry{latest: latest, replacedFrom: replacedFrom}
 	}).(*entry)
-	return e.latest, e.err
+	return e.latest, e.replacedFrom, e.err
 }
 
 var latestVersionIgnoringRetractionsCache par.Cache // path → queryLatestVersionIgnoringRetractions result
diff --git a/src/cmd/go/internal/modload/query.go b/src/cmd/go/internal/modload/query.go
index a7031856ae..6d6bfe774c 100644
--- a/src/cmd/go/internal/modload/query.go
+++ b/src/cmd/go/internal/modload/query.go
@@ -513,9 +513,10 @@ func QueryPackages(ctx context.Context, pattern, query string, current func(stri
 	pkgMods, modOnly, err := QueryPattern(ctx, pattern, query, current, allowed)
 
 	if len(pkgMods) == 0 && err == nil {
+		replacement, _ := Replacement(modOnly.Mod)
 		return nil, &PackageNotInModuleError{
 			Mod:         modOnly.Mod,
-			Replacement: Replacement(modOnly.Mod),
+			Replacement: replacement,
 			Query:       query,
 			Pattern:     pattern,
 		}
@@ -670,9 +671,10 @@ func QueryPattern(ctx context.Context, pattern, query string, current func(strin
 				if err := firstError(m); err != nil {
 					return r, err
 				}
+				replacement, _ := Replacement(r.Mod)
 				return r, &PackageNotInModuleError{
 					Mod:         r.Mod,
-					Replacement: Replacement(r.Mod),
+					Replacement: replacement,
 					Query:       query,
 					Pattern:     pattern,
 				}
@@ -964,7 +966,7 @@ func moduleHasRootPackage(ctx context.Context, m module.Version) (bool, error) {
 // we don't need to verify it in go.sum. This makes 'go list -m -u' faster
 // and simpler.
 func versionHasGoMod(_ context.Context, m module.Version) (bool, error) {
-	_, data, err := rawGoModData(m)
+	_, data, err := rawGoModData(m, "")
 	if err != nil {
 		return false, err
 	}
@@ -1093,7 +1095,7 @@ func (rr *replacementRepo) Stat(rev string) (*modfetch.RevInfo, error) {
 		}
 	}
 
-	if r := Replacement(module.Version{Path: path, Version: v}); r.Path == "" {
+	if r, _ := Replacement(module.Version{Path: path, Version: v}); r.Path == "" {
 		return info, err
 	}
 	return rr.replacementStat(v)
diff --git a/src/cmd/go/internal/modload/vendor.go b/src/cmd/go/internal/modload/vendor.go
index 6dc8b6cf82..b2da3783ea 100644
--- a/src/cmd/go/internal/modload/vendor.go
+++ b/src/cmd/go/internal/modload/vendor.go
@@ -209,7 +209,7 @@ func checkVendorConsistency(index *modFileIndex, modFile *modfile.File) {
 	}
 
 	for _, mod := range vendorReplaced {
-		r := Replacement(mod)
+		r, _ := Replacement(mod)
 		if r == (module.Version{}) {
 			vendErrorf(mod, "is marked as replaced in vendor/modules.txt, but not replaced in go.mod")
 			continue