cmd/go: introduce WriteOpts argument for WriteGoMod

This CL is a no-op, just adding the new options and plumbing it through.
'go get' will use this option to let commitRequirements know whether
toolchain was mentioned explicitly on the command line.

For #57001.

Change-Id: Iee7145f3335e899704df3e98fb840f1aa4063b0c
Reviewed-on: https://go-review.googlesource.com/c/go/+/499555
Run-TryBot: Russ Cox <rsc@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/cmd/go/internal/modcmd/download.go

@@ -187,7 +187,7 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 		// TODO(#45551): In the future, report an error if go.mod or go.sum need to
 		// be updated after loading the build list. This may require setting
 		// the mode to "mod" or "readonly" depending on haveExplicitArgs.
-		if err := modload.WriteGoMod(ctx); err != nil {
+		if err := modload.WriteGoMod(ctx, modload.WriteOpts{}); err != nil {
 			base.Fatalf("go: %v", err)
 		}
 	}
@@ -266,7 +266,7 @@ func runDownload(ctx context.Context, cmd *base.Command, args []string) {
 	// Don't save sums for 'go mod download' without arguments unless we're in
 	// workspace mode; see comment above.
 	if haveExplicitArgs || modload.WorkFilePath() != "" {
-		if err := modload.WriteGoMod(ctx); err != nil {
+		if err := modload.WriteGoMod(ctx, modload.WriteOpts{}); err != nil {
 			base.Errorf("go: %v", err)
 		}
 	}

src/cmd/go/internal/modget/get.go

@@ -379,7 +379,7 @@ func runGet(ctx context.Context, cmd *base.Command, args []string) {
 	// Everything succeeded. Update go.mod.
 	oldReqs := reqsFromGoMod(modload.ModFile())
 
-	if err := modload.WriteGoMod(ctx); err != nil {
+	if err := modload.WriteGoMod(ctx, modload.WriteOpts{}); err != nil {
 		if tooNew, ok := err.(*gover.TooNewError); ok {
 			// This can happen for 'go get go@newversion'
 			// when all the required modules are old enough

src/cmd/go/internal/modload/init.go

@@ -940,7 +940,7 @@ func CreateModFile(ctx context.Context, modPath string) {
 		base.Fatalf("go: %v", err)
 	}
 	requirements = rs
-	if err := commitRequirements(ctx); err != nil {
+	if err := commitRequirements(ctx, WriteOpts{}); err != nil {
 		base.Fatalf("go: %v", err)
 	}
 
@@ -1515,10 +1515,14 @@ func findImportComment(file string) string {
 	return path
 }
 
+// WriteOpts control the behavior of WriteGoMod.
+type WriteOpts struct {
+}
+
 // WriteGoMod writes the current build list back to go.mod.
-func WriteGoMod(ctx context.Context) error {
+func WriteGoMod(ctx context.Context, opts WriteOpts) error {
 	requirements = LoadModFile(ctx)
-	return commitRequirements(ctx)
+	return commitRequirements(ctx, opts)
 }
 
 // commitRequirements ensures go.mod and go.sum are up to date with the current
@@ -1530,7 +1534,7 @@ func WriteGoMod(ctx context.Context) error {
 // go.mod or go.sum are out of date in a semantically significant way.
 //
 // In workspace mode, commitRequirements only writes changes to go.work.sum.
-func commitRequirements(ctx context.Context) (err error) {
+func commitRequirements(ctx context.Context, opts WriteOpts) (err error) {
 	if inWorkspaceMode() {
 		// go.mod files aren't updated in workspace mode, but we still want to
 		// update the go.work.sum file.

src/cmd/go/internal/modload/list.go

@@ -111,7 +111,7 @@ func ListModules(ctx context.Context, args []string, mode ListMode, reuseFile st
 	if err == nil {
 		requirements = rs
 		if !ExplicitWriteGoMod {
-			err = commitRequirements(ctx)
+			err = commitRequirements(ctx, WriteOpts{})
 		}
 	}
 	return mods, err

src/cmd/go/internal/modload/load.go

@@ -450,7 +450,7 @@ func LoadPackages(ctx context.Context, opts PackageOpts, patterns ...string) (ma
 	sort.Strings(loadedPackages)
 
 	if !ExplicitWriteGoMod && opts.ResolveMissingImports {
-		if err := commitRequirements(ctx); err != nil {
+		if err := commitRequirements(ctx, WriteOpts{}); err != nil {
 			base.Fatalf("go: %v", err)
 		}
 	}
@@ -733,7 +733,7 @@ func ImportFromFiles(ctx context.Context, gofiles []string) {
 	requirements = loaded.requirements
 
 	if !ExplicitWriteGoMod {
-		if err := commitRequirements(ctx); err != nil {
+		if err := commitRequirements(ctx, WriteOpts{}); err != nil {
 			base.Fatalf("go: %v", err)
 		}
 	}

src/cmd/go/internal/workcmd/sync.go

@@ -122,7 +122,7 @@ func runSync(ctx context.Context, cmd *base.Command, args []string) {
 			SilenceMissingStdImports: true,
 			SilencePackageErrors:     true,
 		}, "all")
-		modload.WriteGoMod(ctx)
+		modload.WriteGoMod(ctx, modload.WriteOpts{})
 	}
 
 	wf, err := modload.ReadWorkFile(workFilePath)