cmd/cue: implement cue mod init --source

It seems to be really common to invoke `cue mod init`
followed by setting the source field, so make that flow
more straightforward by adding a `--source` flag to
`cue mod init`.

Also update the e2e tests to use it.

Signed-off-by: Roger Peppe <[e-mail]>
Change-Id: I610a851e05b36bf828a21ff6d7bb13daf3cc748b
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1193590
TryBot-Result: CUEcueckoo <[e-mail]>
Unity-Result: CUE porcuepine <[e-mail]>
Reviewed-by: Daniel Martí <[e-mail]>

cmd/cue/cmd/flags.go

···
 	flagRecursive     flagName = "recursive"
 	flagSchema        flagName = "schema"
 	flagSimplify      flagName = "simplify"
+	flagSource        flagName = "source"
 	flagStrict        flagName = "strict"
 	flagTrace         flagName = "trace"
 	flagVerbose       flagName = "verbose"

cmd/cue/cmd/modedit.go

···
 }
 
 func (c *modEditCmd) flagSource(arg string) error {
-	if arg != "git" && arg != "self" {
-		return fmt.Errorf("unrecognized source kind %q", arg)
+	src := &modfile.Source{
+		Kind: arg,
+	}
+	if err := src.Validate(); err != nil {
+		return err
 	}
 	c.addEdit(func(f *modfile.File) error {
-		if f.Source == nil {
-			f.Source = &modfile.Source{}
-		}
-		f.Source.Kind = arg
+		f.Source = src
 		return nil
 	})
 	return nil

cmd/cue/cmd/modinit.go

···
 	}
 
 	cmd.Flags().BoolP(string(flagForce), "f", false, "force moving old-style cue.mod file")
-
+	cmd.Flags().String(string(flagSource), "", "set the source field")
 	return cmd
 }
 
···
 	}
 	mf := &modfile.File{
 		Module: modulePath,
+	}
+	if s := flagSource.String(cmd); s != "" {
+		mf.Source = &modfile.Source{
+			Kind: s,
+		}
+		if err := mf.Source.Validate(); err != nil {
+			return err
+		}
 	}
 	vers := versionForModFile()
 	if vers == "" {

cmd/cue/cmd/testdata/script/modinit_withsource.txtar

···
+# Test that we can use the --source flag to cue mod init.
+
+env CUE_VERSION_OVERRIDE=v0.9.0-alpha.2
+
+mkdir $WORK/test0
+cd $WORK/test0
+exec cue mod init --source self test.example
+cmp cue.mod/module.cue $WORK/want-module.cue-0
+
+mkdir $WORK/test1
+cd $WORK/test1
+exec cue mod init --source git test.example
+cmp cue.mod/module.cue $WORK/want-module.cue-1
+
+mkdir $WORK/test2
+cd $WORK/test2
+! exec cue mod init --source bad test.example
+cmp stderr $WORK/want-stderr
+
+-- want-module.cue-0 --
+module: "test.example"
+language: {
+	version: "v0.9.0-alpha.2"
+}
+source: {
+	kind: "self"
+}
+-- want-module.cue-0 --
+module: "test.example"
+language: {
+	version: "v0.9.0-alpha.2"
+}
+source: {
+	kind: "self"
+}
+-- want-module.cue-1 --
+module: "test.example"
+language: {
+	version: "v0.9.0-alpha.2"
+}
+source: {
+	kind: "git"
+}
+-- want-stderr --
+unrecognized source kind "bad"

internal/_e2e/testdata/script/gcloud_upload.txtar

···
 
 cd publish
 
-exec cue mod init ${MODVER}
-exec cue mod edit --source self
+exec cue mod init --source self ${MODVER}
 exec cue mod publish ${VERSION}
 
 cd ../depend
 
 env-fill out_foo.cue
-exec cue mod init depend.localhost
-exec cue mod edit --source self
+exec cue mod init --source self depend.localhost
 exec cue mod tidy
 exec cue export
 cmp stdout export.golden

internal/_e2e/testdata/script/github_app_private.txtar

···
 
 cd publish
 
-exec cue mod init ${MODVER}
-exec cue mod edit --source self
+exec cue mod init --source self ${MODVER}
 exec cue mod publish ${VERSION}
 
 cd ../depend
 
 env-fill out_foo.cue
-exec cue mod init depend.localhost
-exec cue mod edit --source self
+exec cue mod init --source self depend.localhost
 exec cue mod tidy
 exec cue export
 cmp stdout export.golden

internal/_e2e/testdata/script/github_app_public.txtar

···
 
 cd publish
 
-exec cue mod init ${MODVER}
-exec cue mod edit --source self
+exec cue mod init --source self ${MODVER}
 exec cue mod publish ${VERSION}
 
 cd ../depend
 
 env-fill out_foo.cue
-exec cue mod init depend.localhost
-exec cue mod edit --source self
+exec cue mod init --source self depend.localhost
 exec cue mod tidy
 exec cue export
 cmp stdout export.golden
···
 # so it's not a stable string. We should give the user a short and stable error,
 # and test for it here with a regular expression.
 cd ../publish-different
-exec cue mod init ${MODVER}
-exec cue mod edit --source self
+exec cue mod init --source self ${MODVER}
 ! exec cue mod publish ${VERSION}
 stderr 'cannot tag.*400 Bad Request'
 

mod/modfile/modfile.go

···
 	Kind string `json:"kind"`
 }
 
+// Validate checks that src is well formed.
+func (src *Source) Validate() error {
+	switch src.Kind {
+	case "git", "self":
+		return nil
+	}
+	return fmt.Errorf("unrecognized source kind %q", src.Kind)
+}
+
 // Format returns a formatted representation of f
 // in CUE syntax.
 func (f *File) Format() ([]byte, error) {