Support using command output directly in menuFromCommand custom command prompt

The menuFromCommand option is a little complicated, so I'm adding an easy way to just use the command output directly,
where each line becomes a suggestion, as-is.

Now that we support suggestions in the input prompt, there's less of a need for menuFromCommand, but it probably still
serves some purpose.

In future I want to support this filter/valueFormat/labelFormat thing for suggestions too. I would like to think a little more
about the interface though: is using a regex like we currently do really the simplest approach?

docs/Custom_Command_Keybindings.md

@@ -264,6 +264,20 @@ Here's an example using unnamed groups:
         labelFormat: '{{ .group_1 | green }}'
 ```
 
+Here's an example using a command but not specifying anything else: so each line from the command becomes the value and label of the menu items
+
+```yml
+  - key : 'a'
+    description: 'Checkout a remote branch as FETCH_HEAD'
+    command: "open {{.Form.File | quote}}"
+    context: 'global'
+    prompts:
+      - type: 'menuFromCommand'
+        title: 'File:'
+        key: 'File'
+        command: 'ls'
+```
+
 ## Placeholder values
 
 Your commands can contain placeholder strings using Go's [template syntax](https://jan.newmarch.name/golang/template/chapter-template.html). The template syntax is pretty powerful, letting you do things like conditionals if you want, but for the most part you'll simply want to be accessing the fields on the following objects:

pkg/gui/services/custom_commands/handler_creator.go

@@ -210,7 +210,7 @@ func (self *HandlerCreator) menuPromptFromCommand(prompt *config.CustomCommandPr
 		return self.c.Error(err)
 	}
 
-	menuItems := slices.Map(candidates, func(candidate *commandMenuEntry) *types.MenuItem {
+	menuItems := slices.Map(candidates, func(candidate *commandMenuItem) *types.MenuItem {
 		return &types.MenuItem{
 			LabelColumns: []string{candidate.label},
 			OnPress: func() error {

pkg/gui/services/custom_commands/menu_generator.go

@@ -22,12 +22,41 @@ func NewMenuGenerator(c *common.Common) *MenuGenerator {
 	return &MenuGenerator{c: c}
 }
 
-type commandMenuEntry struct {
+type commandMenuItem struct {
 	label string
 	value string
 }
 
-func (self *MenuGenerator) call(commandOutput, filter, valueFormat, labelFormat string) ([]*commandMenuEntry, error) {
+func (self *MenuGenerator) call(commandOutput, filter, valueFormat, labelFormat string) ([]*commandMenuItem, error) {
+	menuItemFromLine, err := self.getMenuItemFromLinefn(filter, valueFormat, labelFormat)
+	if err != nil {
+		return nil, err
+	}
+
+	menuItems := []*commandMenuItem{}
+	for _, line := range strings.Split(commandOutput, "\n") {
+		if line == "" {
+			continue
+		}
+
+		menuItem, err := menuItemFromLine(line)
+		if err != nil {
+			return nil, err
+		}
+		menuItems = append(menuItems, menuItem)
+	}
+
+	return menuItems, nil
+}
+
+func (self *MenuGenerator) getMenuItemFromLinefn(filter string, valueFormat string, labelFormat string) (func(line string) (*commandMenuItem, error), error) {
+	if filter == "" && valueFormat == "" && labelFormat == "" {
+		// showing command output lines as-is in suggestions panel
+		return func(line string) (*commandMenuItem, error) {
+			return &commandMenuItem{label: line, value: line}, nil
+		}, nil
+	}
+
 	regex, err := regexp.Compile(filter)
 	if err != nil {
 		return nil, errors.New("unable to parse filter regex, error: " + err.Error())
@@ -51,37 +80,25 @@ func (self *MenuGenerator) call(commandOutput, filter, valueFormat, labelFormat
 		labelTemplate = valueTemplate
 	}
 
-	candidates := []*commandMenuEntry{}
-	for _, line := range strings.Split(commandOutput, "\n") {
-		if line == "" {
-			continue
-		}
-
-		candidate, err := self.generateMenuCandidate(
+	return func(line string) (*commandMenuItem, error) {
+		return self.generateMenuItem(
 			line,
 			regex,
 			valueTemplate,
 			labelTemplate,
 		)
-		if err != nil {
-			return nil, err
-		}
-
-		candidates = append(candidates, candidate)
-	}
-
-	return candidates, err
+	}, nil
 }
 
-func (self *MenuGenerator) generateMenuCandidate(
+func (self *MenuGenerator) generateMenuItem(
 	line string,
 	regex *regexp.Regexp,
 	valueTemplate *TrimmerTemplate,
 	labelTemplate *TrimmerTemplate,
-) (*commandMenuEntry, error) {
+) (*commandMenuItem, error) {
 	tmplData := self.parseLine(line, regex)
 
-	entry := &commandMenuEntry{}
+	entry := &commandMenuItem{}
 
 	var err error
 	entry.value, err = valueTemplate.execute(tmplData)

pkg/gui/services/custom_commands/menu_generator_test.go

@@ -14,7 +14,7 @@ func TestMenuGenerator(t *testing.T) {
 		filter      string
 		valueFormat string
 		labelFormat string
-		test        func([]*commandMenuEntry, error)
+		test        func([]*commandMenuItem, error)
 	}
 
 	scenarios := []scenario{
@@ -24,7 +24,7 @@ func TestMenuGenerator(t *testing.T) {
 			"(?P<remote>[a-z_]+)/(?P<branch>.*)",
 			"{{ .branch }}",
 			"Remote: {{ .remote }}",
-			func(actualEntry []*commandMenuEntry, err error) {
+			func(actualEntry []*commandMenuItem, err error) {
 				assert.NoError(t, err)
 				assert.EqualValues(t, "pr-1", actualEntry[0].value)
 				assert.EqualValues(t, "Remote: upstream", actualEntry[0].label)
@@ -36,7 +36,7 @@ func TestMenuGenerator(t *testing.T) {
 			"(?P<remote>[a-z]*)/(?P<branch>.*)",
 			"{{ .branch }}|{{ .remote }}",
 			"",
-			func(actualEntry []*commandMenuEntry, err error) {
+			func(actualEntry []*commandMenuItem, err error) {
 				assert.NoError(t, err)
 				assert.EqualValues(t, "pr-1|upstream", actualEntry[0].value)
 				assert.EqualValues(t, "pr-1|upstream", actualEntry[0].label)
@@ -48,12 +48,36 @@ func TestMenuGenerator(t *testing.T) {
 			"(?P<remote>[a-z]*)/(?P<branch>.*)",
 			"{{ .group_2 }}|{{ .group_1 }}",
 			"Remote: {{ .group_1 }}",
-			func(actualEntry []*commandMenuEntry, err error) {
+			func(actualEntry []*commandMenuItem, err error) {
 				assert.NoError(t, err)
 				assert.EqualValues(t, "pr-1|upstream", actualEntry[0].value)
 				assert.EqualValues(t, "Remote: upstream", actualEntry[0].label)
 			},
 		},
+		{
+			"No named groups",
+			"upstream/pr-1",
+			"([a-z]*)/(.*)",
+			"{{ .group_2 }}|{{ .group_1 }}",
+			"Remote: {{ .group_1 }}",
+			func(actualEntry []*commandMenuItem, err error) {
+				assert.NoError(t, err)
+				assert.EqualValues(t, "pr-1|upstream", actualEntry[0].value)
+				assert.EqualValues(t, "Remote: upstream", actualEntry[0].label)
+			},
+		},
+		{
+			"No filter",
+			"upstream/pr-1",
+			"",
+			"",
+			"",
+			func(actualEntry []*commandMenuItem, err error) {
+				assert.NoError(t, err)
+				assert.EqualValues(t, "upstream/pr-1", actualEntry[0].value)
+				assert.EqualValues(t, "upstream/pr-1", actualEntry[0].label)
+			},
+		},
 	}
 
 	for _, s := range scenarios {