cmd/cue: fix mod edit --source self

The `cue mod edit --source self` wasn't tested and the logic was wrong, so fix it.

Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I809c466c7c76efde34046b83f70c58760dd7f3fd
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1193381
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>

cmd/cue/cmd/modedit.go

@@ -108,7 +108,7 @@ func (c *modEditCmd) addEdit(f func(*modfile.File) error) {
 }
 
 func (c *modEditCmd) flagSource(arg string) error {
-	if arg != "git" && arg != "none" {
+	if arg != "git" && arg != "self" {
 		return fmt.Errorf("unrecognized source kind %q", arg)
 	}
 	c.addEdit(func(f *modfile.File) error {

cmd/cue/cmd/testdata/script/modedit_initial.txtar

@@ -1,3 +1,6 @@
+exec cue mod edit --source self
+cmp cue.mod/module.cue want-module-0
+
 exec cue mod edit --source git
 cmp cue.mod/module.cue want-module-1
 
@@ -20,6 +23,14 @@ cmp cue.mod/module.cue want-module-5
 -- cue.mod/module.cue --
 module: "main.org@v0"
 language: version: "v0.9.0-alpha.0"
+-- want-module-0 --
+module: "main.org@v0"
+language: {
+	version: "v0.9.0-alpha.0"
+}
+source: {
+	kind: "self"
+}
 -- want-module-1 --
 module: "main.org@v0"
 language: {