internal/mod/modload: support adding language version

We want to add a language version declaration to the module.cue
file when it's not present. This enables that.

Also change the modload tests to use `modfile.File.Format` to
format their output, as that's more representative of the
actual use.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I627d2522d6bf7a88a90c9031058addd7b8d5758d
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1173894
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>

cmd/cue/cmd/modtidy.go

@@ -58,7 +58,7 @@ func runModTidy(cmd *Command, args []string) error {
 	if err != nil {
 		return err
 	}
-	mf, err := modload.Load(ctx, os.DirFS(modRoot), ".", reg)
+	mf, err := modload.Tidy(ctx, os.DirFS(modRoot), ".", reg, "")
 	if err != nil {
 		return err
 	}

internal/mod/modload/load.go

@@ -37,9 +37,11 @@ type loader struct {
 	registry      Registry
 }
 
-// Load evaluates all the requirements of the given main module, using the given
+// Tidy evaluates all the requirements of the given main module, using the given
 // registry to download requirements and returns a resolved and tidied module file.
-func Load(ctx context.Context, fsys fs.FS, modRoot string, reg Registry) (*modfile.File, error) {
+// If there's no language version in the module file and cueVers is non-empty
+// it will be used to populate the language version field.
+func Tidy(ctx context.Context, fsys fs.FS, modRoot string, reg Registry, cueVers string) (*modfile.File, error) {
 	modFilePath := path.Join(modRoot, "cue.mod/module.cue")
 	data, err := fs.ReadFile(fsys, modFilePath)
 	if err != nil {
@@ -79,15 +81,20 @@ func Load(ctx context.Context, fsys fs.FS, modRoot string, reg Registry) (*modfi
 	if err != nil {
 		return nil, fmt.Errorf("cannot tidy requirements: %v", err)
 	}
-	return modfileFromRequirements(mf, rs), nil
+	return modfileFromRequirements(mf, rs, cueVers), nil
 }
 
-func modfileFromRequirements(old *modfile.File, rs *modrequirements.Requirements) *modfile.File {
+func modfileFromRequirements(old *modfile.File, rs *modrequirements.Requirements, cueVers string) *modfile.File {
 	mf := &modfile.File{
 		Module:   old.Module,
 		Language: old.Language,
 		Deps:     make(map[string]*modfile.Dep),
 	}
+	if cueVers != "" && (mf.Language == nil || mf.Language.Version == "") {
+		mf.Language = &modfile.Language{
+			Version: cueVers,
+		}
+	}
 	defaults := rs.DefaultMajorVersions()
 	for _, v := range rs.RootModules() {
 		mf.Deps[v.Path()] = &modfile.Dep{

internal/mod/modload/load_test.go

@@ -16,7 +16,6 @@ import (
 	"github.com/google/go-cmp/cmp"
 	"golang.org/x/tools/txtar"
 
-	"cuelang.org/go/cue/cuecontext"
 	"cuelang.org/go/internal/mod/modfile"
 	"cuelang.org/go/internal/mod/modpkgload"
 	"cuelang.org/go/internal/mod/modregistry"
@@ -39,14 +38,16 @@ func TestLoad(t *testing.T) {
 			want, err := fs.ReadFile(tfs, "want")
 			qt.Assert(t, qt.IsNil(err))
 
+			cueVers, _ := fs.ReadFile(tfs, "cue-version")
+
 			var out strings.Builder
-			mf, err := Load(context.Background(), tfs, ".", reg)
+			mf, err := Tidy(context.Background(), tfs, ".", reg, strings.TrimSpace(string(cueVers)))
 			if err != nil {
 				fmt.Fprintf(&out, "error: %v\n", err)
 			} else {
-				ctx := cuecontext.New()
-				v := ctx.Encode(mf)
-				fmt.Fprintln(&out, v)
+				data, err := mf.Format()
+				qt.Assert(t, qt.IsNil(err))
+				out.Write(data)
 			}
 			if diff := cmp.Diff(string(want), out.String()); diff != "" {
 				t.Log("actual result:\n", out.String())

internal/mod/modload/testdata/addversion.txtar

@@ -0,0 +1,12 @@
+# Test that a version is added if not present
+-- cue-version --
+v1.2.3
+-- want --
+module: "main.org@v0"
+language: {
+	version: "v1.2.3"
+}
+-- cue.mod/module.cue --
+module: "main.org@v0"
+-- main.cue --
+package main

internal/mod/modload/testdata/canuseprerelease.txtar

@@ -2,12 +2,10 @@
 # no stable releases available.
 
 -- want --
-{
-	module: "main.org@v0"
-	deps: {
-		"example.com@v0": {
-			v: "v0.0.3-alpha"
-		}
+module: "main.org@v0"
+deps: {
+	"example.com@v0": {
+		v: "v0.0.3-alpha"
 	}
 }
 -- cue.mod/module.cue --

internal/mod/modload/testdata/implied-major-version-with-explicit-default.txtar

@@ -1,13 +1,11 @@
 # This test checks we can have have an import with an implied major version
 # when there's an explicit default in the module file.
 -- want --
-{
-	module: "main.org@v0"
-	deps: {
-		"example.com@v0": {
-			v:       "v0.0.1"
-			default: true
-		}
+module: "main.org@v0"
+deps: {
+	"example.com@v0": {
+		v:       "v0.0.1"
+		default: true
 	}
 }
 -- cue.mod/module.cue --

internal/mod/modload/testdata/implied-major-version-without-explicit-default.txtar

@@ -1,13 +1,11 @@
 # This test checks we can have have an import with an implied major version
 # when there's no explicit default in the module file.
 -- want --
-{
-	module: "main.org@v0"
-	deps: {
-		"example.com@v1": {
-			v:       "v1.0.0"
-			default: true
-		}
+module: "main.org@v0"
+deps: {
+	"example.com@v1": {
+		v:       "v1.0.0"
+		default: true
 	}
 }
 -- cue.mod/module.cue --

internal/mod/modload/testdata/nested-deps.txtar

@@ -2,21 +2,19 @@
 # and a module that's unused.
 
 -- want --
-{
-	module: "main.org@v0"
-	deps: {
-		"bar.com@v0": {
-			v: "v0.5.0"
-		}
-		"baz.org@v0": {
-			v: "v0.10.1"
-		}
-		"example.com@v0": {
-			v: "v0.0.1"
-		}
-		"foo.com/bar/hello@v0": {
-			v: "v0.2.3"
-		}
+module: "main.org@v0"
+deps: {
+	"bar.com@v0": {
+		v: "v0.5.0"
+	}
+	"baz.org@v0": {
+		v: "v0.10.1"
+	}
+	"example.com@v0": {
+		v: "v0.0.1"
+	}
+	"foo.com/bar/hello@v0": {
+		v: "v0.2.3"
 	}
 }
 -- cue.mod/module.cue --

internal/mod/modload/testdata/noaddversion.txtar

@@ -0,0 +1,13 @@
+# Test that a version is not added if present
+-- cue-version --
+v1.2.3
+-- want --
+module: "main.org@v0"
+language: {
+	version: "v1.0.3"
+}
+-- cue.mod/module.cue --
+module: "main.org@v0"
+language: version: "v1.0.3"
+-- main.cue --
+package main

internal/mod/modload/testdata/preferstable.txtar

@@ -2,12 +2,10 @@
 # pre-releases.
 
 -- want --
-{
-	module: "main.org@v0"
-	deps: {
-		"example.com@v0": {
-			v: "v0.0.1"
-		}
+module: "main.org@v0"
+deps: {
+	"example.com@v0": {
+		v: "v0.0.1"
 	}
 }
 -- cue.mod/module.cue --

internal/mod/modload/testdata/stdlibpackagenotfound.txtar

@@ -2,10 +2,7 @@
 # the standard library but that doesn't exist.
 
 -- want --
-{
-	module: "main.org@v0"
-	deps: {}
-}
+module: "main.org@v0"
 -- cue.mod/module.cue --
 module: "main.org@v0"