[dev.cmdgo] cmd/go: fix calls to modFileGoVersion to pass in modFile

Before this change, we were arbitrarily picking a module to get the Go
version from in calls to modFileGoVersion. We now pass in the modFile to
modFileGoVersion when we have the file. Most of the calls were to get
the goVersion argument for commitRequirements, so now we have
commitRequirements call modFileGoVersion on the modFile directly
One of the calls to commitRequirements (when running go mod tidy with
a different Go version) passed in a new go version to update the file
to. Now, the modFile is updated before calling commitRequirements.

For the remaining cases of modFileGoVersion, it's replaced by a call to
the new (*MainModuleSet).GoVersion function, which either returns the go
version on the workspace file (in workspace mode) or the version of the
single go.mod file.

Change-Id: Ie88c3ca76c7f29ffc4faa16bb76f6cb7eccb5029
Reviewed-on: https://go-review.googlesource.com/c/go/+/344749
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>

5 files changed, 64 insertions, 40 deletions

diff --git a/src/cmd/go/internal/modload/buildlist.go b/src/cmd/go/internal/modload/buildlist.go
index 14379b4c3c..94414278ab 100644
--- a/src/cmd/go/internal/modload/buildlist.go
+++ b/src/cmd/go/internal/modload/buildlist.go
@@ -461,7 +461,7 @@ func LoadModGraph(ctx context.Context, goVersion string) *ModuleGraph {
 		base.Fatalf("go: %v", err)
 	}
 
-	commitRequirements(ctx, modFileGoVersion(), rs)
+	commitRequirements(ctx, rs)
 	return mg
 }
 
@@ -527,7 +527,7 @@ func EditBuildList(ctx context.Context, add, mustSelect []module.Version) (chang
 	if err != nil {
 		return false, err
 	}
-	commitRequirements(ctx, modFileGoVersion(), rs)
+	commitRequirements(ctx, rs)
 	return changed, err
 }
 
diff --git a/src/cmd/go/internal/modload/init.go b/src/cmd/go/internal/modload/init.go
index ab6733830f..b845842a7f 100644
--- a/src/cmd/go/internal/modload/init.go
+++ b/src/cmd/go/internal/modload/init.go
@@ -59,8 +59,9 @@ var (
 	// roots are required but MainModules hasn't been initialized yet. Set to
 	// the modRoots of the main modules.
 	// modRoots != nil implies len(modRoots) > 0
-	modRoots []string
-	gopath   string
+	modRoots          []string
+	gopath            string
+	workFileGoVersion string
 )
 
 // Variable set in InitWorkfile
@@ -91,6 +92,8 @@ type MainModuleSet struct {
 
 	modContainingCWD module.Version
 
+	workFileGoVersion string
+
 	indexMu sync.Mutex
 	indices map[module.Version]*modFileIndex
 }
@@ -190,6 +193,20 @@ func (mms *MainModuleSet) ModContainingCWD() module.Version {
 	return mms.modContainingCWD
 }
 
+// GoVersion returns the go version set on the single module, in module mode,
+// or the go.work file in workspace mode.
+func (mms *MainModuleSet) GoVersion() string {
+	if !inWorkspaceMode() {
+		return modFileGoVersion(mms.ModFile(mms.mustGetSingleMainModule()))
+	}
+	v := mms.workFileGoVersion
+	if v == "" {
+		// Fall back to 1.18 for go.work files.
+		v = "1.18"
+	}
+	return v
+}
+
 var MainModules *MainModuleSet
 
 type Root int
@@ -374,7 +391,7 @@ func Init() {
 
 	if inWorkspaceMode() {
 		var err error
-		modRoots, err = loadWorkFile(workFilePath)
+		workFileGoVersion, modRoots, err = loadWorkFile(workFilePath)
 		if err != nil {
 			base.Fatalf("reading go.work: %v", err)
 		}
@@ -536,16 +553,19 @@ func (goModDirtyError) Error() string {
 
 var errGoModDirty error = goModDirtyError{}
 
-func loadWorkFile(path string) (modRoots []string, err error) {
+func loadWorkFile(path string) (goVersion string, modRoots []string, err error) {
 	_ = TODOWorkspaces("Clean up and write back the go.work file: add module paths for workspace modules.")
 	workDir := filepath.Dir(path)
 	workData, err := lockedfile.Read(path)
 	if err != nil {
-		return nil, err
+		return "", nil, err
 	}
 	wf, err := modfile.ParseWork(path, workData, nil)
 	if err != nil {
-		return nil, err
+		return "", nil, err
+	}
+	if wf.Go != nil {
+		goVersion = wf.Go.Version
 	}
 	seen := map[string]bool{}
 	for _, d := range wf.Directory {
@@ -554,12 +574,12 @@ func loadWorkFile(path string) (modRoots []string, err error) {
 			modRoot = filepath.Join(workDir, modRoot)
 		}
 		if seen[modRoot] {
-			return nil, fmt.Errorf("path %s appears multiple times in workspace", modRoot)
+			return "", nil, fmt.Errorf("path %s appears multiple times in workspace", modRoot)
 		}
 		seen[modRoot] = true
 		modRoots = append(modRoots, modRoot)
 	}
-	return modRoots, nil
+	return goVersion, modRoots, nil
 }
 
 // LoadModFile sets Target and, if there is a main module, parses the initial
@@ -582,7 +602,7 @@ func loadWorkFile(path string) (modRoots []string, err error) {
 func LoadModFile(ctx context.Context) *Requirements {
 	rs, needCommit := loadModFile(ctx)
 	if needCommit {
-		commitRequirements(ctx, modFileGoVersion(), rs)
+		commitRequirements(ctx, rs)
 	}
 	return rs
 }
@@ -602,7 +622,7 @@ func loadModFile(ctx context.Context) (rs *Requirements, needCommit bool) {
 	if len(modRoots) == 0 {
 		_ = TODOWorkspaces("Instead of creating a fake module with an empty modroot, make MainModules.Len() == 0 mean that we're in module mode but not inside any module.")
 		mainModule := module.Version{Path: "command-line-arguments"}
-		MainModules = makeMainModules([]module.Version{mainModule}, []string{""}, []*modfile.File{nil}, []*modFileIndex{nil})
+		MainModules = makeMainModules([]module.Version{mainModule}, []string{""}, []*modfile.File{nil}, []*modFileIndex{nil}, "")
 		goVersion := LatestGoVersion()
 		rawGoVersion.Store(mainModule, goVersion)
 		requirements = newRequirements(modDepthFromGoVersion(goVersion), nil, nil)
@@ -652,7 +672,7 @@ func loadModFile(ctx context.Context) (rs *Requirements, needCommit bool) {
 		}
 	}
 
-	MainModules = makeMainModules(mainModules, modRoots, modFiles, indices)
+	MainModules = makeMainModules(mainModules, modRoots, modFiles, indices, workFileGoVersion)
 	setDefaultBuildMod() // possibly enable automatic vendoring
 	rs = requirementsFromModFiles(ctx, modFiles)
 
@@ -702,7 +722,7 @@ func loadModFile(ctx context.Context) (rs *Requirements, needCommit bool) {
 				}
 			}
 		} else {
-			rawGoVersion.Store(mainModule, modFileGoVersion())
+			rawGoVersion.Store(mainModule, modFileGoVersion(MainModules.ModFile(mainModule)))
 		}
 	}
 
@@ -756,7 +776,7 @@ func CreateModFile(ctx context.Context, modPath string) {
 	fmt.Fprintf(os.Stderr, "go: creating new go.mod: module %s\n", modPath)
 	modFile := new(modfile.File)
 	modFile.AddModuleStmt(modPath)
-	MainModules = makeMainModules([]module.Version{modFile.Module.Mod}, []string{modRoot}, []*modfile.File{modFile}, []*modFileIndex{nil})
+	MainModules = makeMainModules([]module.Version{modFile.Module.Mod}, []string{modRoot}, []*modfile.File{modFile}, []*modFileIndex{nil}, "")
 	addGoStmt(modFile, modFile.Module.Mod, LatestGoVersion()) // Add the go directive before converted module requirements.
 
 	convertedFrom, err := convertLegacyConfig(modFile, modRoot)
@@ -772,7 +792,7 @@ func CreateModFile(ctx context.Context, modPath string) {
 	if err != nil {
 		base.Fatalf("go: %v", err)
 	}
-	commitRequirements(ctx, modFileGoVersion(), rs)
+	commitRequirements(ctx, rs)
 
 	// Suggest running 'go mod tidy' unless the project is empty. Even if we
 	// imported all the correct requirements above, we're probably missing
@@ -880,7 +900,7 @@ func AllowMissingModuleImports() {
 
 // makeMainModules creates a MainModuleSet and associated variables according to
 // the given main modules.
-func makeMainModules(ms []module.Version, rootDirs []string, modFiles []*modfile.File, indices []*modFileIndex) *MainModuleSet {
+func makeMainModules(ms []module.Version, rootDirs []string, modFiles []*modfile.File, indices []*modFileIndex, workFileGoVersion string) *MainModuleSet {
 	for _, m := range ms {
 		if m.Version != "" {
 			panic("mainModulesCalled with module.Version with non empty Version field: " + fmt.Sprintf("%#v", m))
@@ -888,12 +908,13 @@ func makeMainModules(ms []module.Version, rootDirs []string, modFiles []*modfile
 	}
 	modRootContainingCWD := findModuleRoot(base.Cwd())
 	mainModules := &MainModuleSet{
-		versions:    ms[:len(ms):len(ms)],
-		inGorootSrc: map[module.Version]bool{},
-		pathPrefix:  map[module.Version]string{},
-		modRoot:     map[module.Version]string{},
-		modFiles:    map[module.Version]*modfile.File{},
-		indices:     map[module.Version]*modFileIndex{},
+		versions:          ms[:len(ms):len(ms)],
+		inGorootSrc:       map[module.Version]bool{},
+		pathPrefix:        map[module.Version]string{},
+		modRoot:           map[module.Version]string{},
+		modFiles:          map[module.Version]*modfile.File{},
+		indices:           map[module.Version]*modFileIndex{},
+		workFileGoVersion: workFileGoVersion,
 	}
 	for i, m := range ms {
 		mainModules.pathPrefix[m] = m.Path
@@ -958,7 +979,7 @@ func requirementsFromModFiles(ctx context.Context, modFiles []*modfile.File) *Re
 		}
 	}
 	module.Sort(roots)
-	rs := newRequirements(modDepthFromGoVersion(modFileGoVersion()), roots, direct)
+	rs := newRequirements(modDepthFromGoVersion(MainModules.GoVersion()), roots, direct)
 	return rs
 }
 
@@ -1315,12 +1336,13 @@ func WriteGoMod(ctx context.Context) {
 	if !allowWriteGoMod {
 		panic("WriteGoMod called while disallowed")
 	}
-	commitRequirements(ctx, modFileGoVersion(), LoadModFile(ctx))
+	commitRequirements(ctx, LoadModFile(ctx))
 }
 
 // commitRequirements writes sets the global requirements variable to rs and
 // writes its contents back to the go.mod file on disk.
-func commitRequirements(ctx context.Context, goVersion string, rs *Requirements) {
+// goVersion, if non-empty, is used to set the version on the go.mod file.
+func commitRequirements(ctx context.Context, rs *Requirements) {
 	requirements = rs
 
 	if !allowWriteGoMod {
@@ -1352,10 +1374,10 @@ func commitRequirements(ctx context.Context, goVersion string, rs *Requirements)
 			Indirect: !rs.direct[m.Path],
 		})
 	}
-	if goVersion != "" {
-		modFile.AddGoStmt(goVersion)
+	if modFile.Go == nil || modFile.Go.Version == "" {
+		modFile.AddGoStmt(modFileGoVersion(modFile))
 	}
-	if semver.Compare("v"+modFileGoVersion(), separateIndirectVersionV) < 0 {
+	if semver.Compare("v"+modFileGoVersion(modFile), separateIndirectVersionV) < 0 {
 		modFile.SetRequire(list)
 	} else {
 		modFile.SetRequireSeparateIndirect(list)
diff --git a/src/cmd/go/internal/modload/list.go b/src/cmd/go/internal/modload/list.go
index 1862bef494..9c5018f340 100644
--- a/src/cmd/go/internal/modload/list.go
+++ b/src/cmd/go/internal/modload/list.go
@@ -72,7 +72,7 @@ func ListModules(ctx context.Context, args []string, mode ListMode) ([]*modinfo.
 	}
 
 	if err == nil {
-		commitRequirements(ctx, modFileGoVersion(), rs)
+		commitRequirements(ctx, rs)
 	}
 	return mods, err
 }
diff --git a/src/cmd/go/internal/modload/load.go b/src/cmd/go/internal/modload/load.go
index c9004ff796..efe6ad1319 100644
--- a/src/cmd/go/internal/modload/load.go
+++ b/src/cmd/go/internal/modload/load.go
@@ -407,11 +407,17 @@ func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (ma
 				base.Fatalf("go: %v", err)
 			}
 		}
+
+		// Update the go.mod file's Go version if necessary.
+		modFile := MainModules.ModFile(MainModules.mustGetSingleMainModule())
+		if ld.GoVersion != "" {
+			modFile.AddGoStmt(ld.GoVersion)
+		}
 	}
 
 	// Success! Update go.mod and go.sum (if needed) and return the results.
 	loaded = ld
-	commitRequirements(ctx, loaded.GoVersion, loaded.requirements)
+	commitRequirements(ctx, loaded.requirements)
 
 	for _, pkg := range ld.pkgs {
 		if !pkg.isTest() {
@@ -678,7 +684,7 @@ func ImportFromFiles(ctx context.Context, gofiles []string) {
 			return roots
 		},
 	})
-	commitRequirements(ctx, loaded.GoVersion, loaded.requirements)
+	commitRequirements(ctx, loaded.requirements)
 }
 
 // DirImportPath returns the effective import path for dir,
@@ -960,7 +966,7 @@ func loadFromRoots(ctx context.Context, params loaderParams) *loader {
 	}
 
 	if ld.GoVersion == "" {
-		ld.GoVersion = modFileGoVersion()
+		ld.GoVersion = MainModules.GoVersion()
 
 		if ld.Tidy && semver.Compare("v"+ld.GoVersion, "v"+LatestGoVersion()) > 0 {
 			ld.errorf("go mod tidy: go.mod file indicates go %s, but maximum supported version is %s\n", ld.GoVersion, LatestGoVersion())
@@ -1836,7 +1842,7 @@ func (ld *loader) checkTidyCompatibility(ctx context.Context, rs *Requirements)
 		fmt.Fprintln(os.Stderr)
 
 		goFlag := ""
-		if ld.GoVersion != modFileGoVersion() {
+		if ld.GoVersion != MainModules.GoVersion() {
 			goFlag = " -go=" + ld.GoVersion
 		}
 
diff --git a/src/cmd/go/internal/modload/modfile.go b/src/cmd/go/internal/modload/modfile.go
index 09e9c67659..463869910c 100644
--- a/src/cmd/go/internal/modload/modfile.go
+++ b/src/cmd/go/internal/modload/modfile.go
@@ -57,12 +57,8 @@ const (
 )
 
 // modFileGoVersion returns the (non-empty) Go version at which the requirements
-// in modFile are intepreted, or the latest Go version if modFile is nil.
-func modFileGoVersion() string {
-	_ = TODOWorkspaces("this is obviously wrong.")
-	// Yes we're picking arbitrarily, we'll have to pass through the version
-	// we care about
-	modFile := MainModules.ModFile(MainModules.Versions()[0])
+// in modFile are interpreted, or the latest Go version if modFile is nil.
+func modFileGoVersion(modFile *modfile.File) string {
 	if modFile == nil {
 		return LatestGoVersion()
 	}