Change limactl list --format json not to include empty objects

Unlike the YAML encoder, the JSON encoder will encode empty structs
even when they have the `json:",omitempty"` tag (it will only emit nil
pointers to structs).

This commit repeatedly removes empty objects until the result no
longer gets any shorter. It doesn't check for the omitempty tag, but
we have that tag set on every struct.

Example: this removes `"vmOpts":{"qemu":{},"vz":{"rosetta":{}}}`.

Signed-off-by: Jan Dubois <jan.dubois@suse.com>

Author: jandubois

cmd/limactl/list.go

@@ -249,25 +249,43 @@ func listAction(cmd *cobra.Command, args []string) error {
 	}
 
 	if format == "json" {
+		// The JSON encoder will create empty objects (YAML maps), even when they have the ",omitempty" tag.
+		deleteEmptyObjects := `del(.. | select(tag == "!!map" and length == 0))`
+		yqExpr += " | " + deleteEmptyObjects
+
 		encoderPrefs := yqlib.ConfiguredJSONPreferences.Copy()
-		if isTTY {
-			// Using non-0 indent means the instance will be printed over multiple lines,
-			// so is no longer in JSON Lines format. This is a compromise for readability.
-			encoderPrefs.Indent = 4
-			encoderPrefs.ColorsEnabled = true
-		} else {
-			encoderPrefs.Indent = 0
-			encoderPrefs.ColorsEnabled = false
-		}
-		encoder := yqlib.NewJSONEncoder(encoderPrefs)
+		encoderPrefs.ColorsEnabled = false
+		encoderPrefs.Indent = 0
+		plainEncoder := yqlib.NewJSONEncoder(encoderPrefs)
+		// Using non-0 indent means the instance will be printed over multiple lines,
+		// so is no longer in JSON Lines format. This is a compromise for readability.
+		encoderPrefs.Indent = 4
+		encoderPrefs.ColorsEnabled = true
+		colorEncoder := yqlib.NewJSONEncoder(encoderPrefs)
 
 		// Each line contains the JSON object for one Lima instance.
 		scanner := bufio.NewScanner(buf)
 		for scanner.Scan() {
 			var str string
-			if str, err = yqutil.EvaluateExpressionWithEncoder(yqExpr, scanner.Text(), encoder); err != nil {
+			if str, err = yqutil.EvaluateExpressionWithEncoder(yqExpr, scanner.Text(), plainEncoder); err != nil {
 				return err
 			}
+			// Repeatedly delete empty objects until there are none left.
+			for {
+				length := len(str)
+				if str, err = yqutil.EvaluateExpressionWithEncoder(deleteEmptyObjects, str, plainEncoder); err != nil {
+					return err
+				}
+				if len(str) >= length {
+					break
+				}
+			}
+			if isTTY {
+				// pretty-print and colorize the output
+				if str, err = yqutil.EvaluateExpressionWithEncoder(".", str, colorEncoder); err != nil {
+					return err
+				}
+			}
 			if _, err = fmt.Fprint(cmd.OutOrStdout(), str); err != nil {
 				return err
 			}

hack/bats/tests/01-list.bats

@@ -20,20 +20,6 @@ local_setup() {
     export LIMA_HOME="${LOCAL_LIMA_HOME:?}"
 }
 
-# In Go templates "{{json .}}" will encode empty maps (e.g. "foo": {}) even if the
-# map has the "json:",omitempty" tag. "{{yaml .}}" does omit empty maps, so remove
-# them from the JSON output to make it comparable to the YAML one.
-#
-# TODO should we modify `limactl list` to remove empty maps by default
-# since we pass the output through yq anyways?
-canonical_json() {
-    local empty_maps='.. | select(tag == "!!map" and length == 0)'
-    while limactl yq --exit-status --input-format json "[${empty_maps}] | length > 0" <<<"$output" >/dev/null 2>&1; do
-        run -0 limactl yq --input-format json --output-format json --indent 0 "del(${empty_maps})" <<<"$output"
-    done
-
-}
-
 @test 'list with no running instances shows a warning and exits without error' {
     export LIMA_HOME="$BATS_TEST_TMPDIR"
     run_e -0 limactl list
@@ -101,9 +87,8 @@ canonical_json() {
 }
 
 @test '--format YAML returns YAML documents' {
-    # save canonical JSON output with empty maps removed, for comparison
+    # save JSON output for comparison
     run -0 limactl ls foo bar --format json
-    canonical_json
     json=$output
 
     run -0 limactl ls --format yaml foo bar
@@ -121,7 +106,7 @@ canonical_json() {
     run -0 limactl yq --input-format yaml --output-format json  --indent 0 "." <<<"$yaml"
     assert_output_lines_count 2
 
-    # verify it matches the canonical JSON output
+    # verify it matches the JSON output
     assert_output "$json"
 
 }
@@ -148,14 +133,13 @@ canonical_json() {
     run -0 limactl yq --input-format json --output-format json  --indent 0 "." <<<"$output"
     assert_output_lines_count 2
 
-    # compare to the regular --format json output
+    # compare to the plain (uncolorized) json output
     assert_output "$json"
 }
 
 @test 'YAML output to terminal is colorized, but semantically identical' {
-    # save canonical output without colors and empty maps removed
+    # save uncolorized JSON output
     run -0 limactl ls foo bar --format json
-    canonical_json
     json=$output
 
     # colorize output even when stdout is not a tty
@@ -179,7 +163,7 @@ canonical_json() {
     run -0 limactl yq --indent 0 --input-format yaml --output-format json "." <<<"$yaml"
     assert_output_lines_count 2
 
-    # verify it matches the canonical JSON output
+    # verify it matches the JSON output
     assert_output "$json"
 }