cmd/cue: implement cue import --dry-run

The flag had been documented and declared for a while,
but it never did anything - nor did we have any tests for it.
Its presence aligns with the docs, and makes a new encoding test easier.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: If149e079a8310bbd9d06330256cbd471bfe0f95a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1198967
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Unity-Result: CUE porcuepine <[email protected]>

cmd/cue/cmd/import.go

@@ -258,7 +258,7 @@ Example:
 	addOrphanFlags(cmd.Flags())
 
 	cmd.Flags().Bool(string(flagFiles), false, "split multiple entries into different files")
-	cmd.Flags().Bool(string(flagDryRun), false, "only run simulation")
+	cmd.Flags().Bool(string(flagDryRun), false, "show what files would be created")
 	cmd.Flags().BoolP(string(flagRecursive), "R", false, "recursively parse string values")
 	cmd.Flags().StringArray(string(flagExt), nil, "match files with these extensions")
 
@@ -442,7 +442,7 @@ func getFilename(b *buildPlan, f *ast.File, root string, force bool) (filename s
 			if !force {
 				// TODO: mimic old behavior: write to stderr, but do not exit
 				// with error code. Consider what is best to do here.
-				stderr := b.cmd.Command.OutOrStderr()
+				stderr := b.cmd.OutOrStderr()
 				if root != "" {
 					cueFile, _ = filepath.Rel(root, cueFile)
 				}
@@ -478,6 +478,15 @@ func handleFile(b *buildPlan, f *ast.File) (err error) {
 }
 
 func writeFile(p *buildPlan, f *ast.File, cueFile string) error {
+	if flagDryRun.Bool(p.cmd) {
+		cueFile, err := filepath.Rel(rootWorkingDir, cueFile)
+		if err != nil {
+			return err
+		}
+		stderr := p.cmd.OutOrStderr()
+		fmt.Fprintf(stderr, "importing into %s\n", cueFile)
+		return nil
+	}
 	b, err := format.Node(f, format.Simplify())
 	if err != nil {
 		return fmt.Errorf("error formatting file: %v", err)

cmd/cue/cmd/testdata/script/encoding_jsonl.txtar

@@ -32,21 +32,15 @@ cmp stdout export-one.stdout
 # TODO(mvdan): note that `cue import --dry-run` does not work,
 # so we need to use rm and stderr checks to ensure we create the files we expect.
 
-! exec cue import --list .
+! exec cue import --list --dry-run .
 stderr 'invalid JSON .*input-many.json.* after top-level value'
 rm input-many.json
 
-rm input-jsonl.cue input-ldjson.cue input-one.cue
-exec cue import --list .
-! stderr 'Skipping file.*already exists'
-exists input-jsonl.cue input-ldjson.cue input-one.cue
-! exists input-none.cue input-ndjson.cue
+exec cue import --list --dry-run .
+cmp stderr import.stderr
 
-rm input-jsonl.cue input-ldjson.cue input-one.cue
-exec cue import json --list .
-! stderr 'Skipping file.*already exists'
-exists input-jsonl.cue input-ldjson.cue input-one.cue
-! exists input-none.cue input-ndjson.cue
+exec cue import json --list --dry-run .
+cmp stderr import.stderr
 
 -- input-none.none --
 {"a": "one"}
@@ -81,3 +75,7 @@ exists input-jsonl.cue input-ldjson.cue input-one.cue
 {"a": "json one"}
 {"b": "json two"}
 {"c1": "json three", "c2": "json four"}
+-- import.stderr --
+importing into input-jsonl.cue
+importing into input-ldjson.cue
+importing into input-one.cue