cmd/cue: add language version in "mod init"

We want the language version to be reflected in the module file.

Also check that `cue mod tidy` is a no-op after running `cue mod init`.

Fixes #2808.

Signed-off-by: Roger Peppe <[email protected]>
Change-Id: I31339c34f6f26175a6b04fb0431238c88d413725
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1177110
Reviewed-by: Daniel Martí <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

cmd/cue/cmd/mod.go

@@ -25,6 +25,7 @@ import (
 
 	"cuelang.org/go/internal/mod/modfile"
 	"cuelang.org/go/internal/mod/module"
+	gomodule "golang.org/x/mod/module"
 )
 
 func newModCmd(c *Command) *cobra.Command {
@@ -125,7 +126,11 @@ func runModInit(cmd *Command, args []string) (err error) {
 	}
 	mf := &modfile.File{
 		Module: modulePath,
-		// TODO Language
+	}
+	if vers := versionForModFile(); vers != "" {
+		mf.Language = &modfile.Language{
+			Version: vers,
+		}
 	}
 
 	err = os.Mkdir(mod, 0755)
@@ -184,3 +189,17 @@ func backport(mod, cwd string) error {
 
 	return nil
 }
+
+func versionForModFile() string {
+	bi, _ := readBuildInfo()
+	version := cueVersion(bi)
+	if gomodule.IsPseudoVersion(version) {
+		// If we have a version like v0.7.1-0.20240130142347-7855e15cb701
+		// we want it to turn into the base version (v0.7.0 in that example).
+		// If there's no base version (e.g. v0.0.0-...) then PseudoVersionBase
+		// will return the empty string, which is exactly what we want
+		// because we don't want to put v0.0.0 in a module.cue file.
+		version, _ = gomodule.PseudoVersionBase(version)
+	}
+	return version
+}

cmd/cue/cmd/modtidy.go

@@ -22,7 +22,6 @@ import (
 	"path/filepath"
 
 	"github.com/spf13/cobra"
-	gomodule "golang.org/x/mod/module"
 
 	"cuelang.org/go/internal/mod/modload"
 )
@@ -69,17 +68,7 @@ func runModTidy(cmd *Command, args []string) error {
 	if err != nil {
 		return err
 	}
-	bi, _ := readBuildInfo()
-	version := cueVersion(bi)
-	if gomodule.IsPseudoVersion(version) {
-		// If we have a version like v0.7.1-0.20240130142347-7855e15cb701
-		// we want it to turn into the base version (v0.7.0 in that example).
-		// If there's no base version (e.g. v0.0.0-...) then PseudoVersionBase
-		// will return the empty string, which is exactly what we want
-		// because we don't want to put v0.0.0 in a module.cue file.
-		version, _ = gomodule.PseudoVersionBase(version)
-	}
-	mf, err := modload.Tidy(ctx, os.DirFS(modRoot), ".", reg, version)
+	mf, err := modload.Tidy(ctx, os.DirFS(modRoot), ".", reg, versionForModFile())
 	if err != nil {
 		return err
 	}

cmd/cue/cmd/testdata/script/modinit_with_version.txtar

@@ -0,0 +1,18 @@
+# Check that cue mod init adds the language version.
+env CUE_VERSION_OVERRIDE=v0.1.2
+exec cue mod init foo.example
+cmp cue.mod/module.cue want-module
+
+# cue mod tidy should be a no-op after cue mod init
+exec cue mod tidy
+cmp cue.mod/module.cue want-module
+
+-- want-module --
+module: "foo.example@v0"
+language: {
+	version: "v0.1.2"
+}
+-- _registry/example.com_e_v0.0.1/cue.mod/module.cue --
+module: "example.com/e@v0"
+-- _registry/example.com_e_v0.0.1/main.cue --
+package e