almost working show VERSION command

shows slightly to much (2 characters at the end)

cmd/show.go

@@ -13,9 +13,33 @@ var shouldShowPlain bool
 
 // showCmd represents the show command
 var showCmd = &cobra.Command{
-	Use:   "show",
+	Use:   "show [VERSION|latest|next|unreleased]",
 	Short: "Displays the contents of the nearest changelog.",
-	Long:  `Displays the contents of the nearest changelog.`,
+	Long: `Displays the contents of the nearest changelog.
+
+	If a VERSION (e.g. "1.2.3") is specified, only the release notes for that given version will be shown.
+	Instead of a specific version you can also use one of the following aliases:
+	- "latest" will show the latest release
+	- "next" or "unreleased" will show the contents of the [Unreleased]
+	`,
+	Args: cobra.MaximumNArgs(1),
+	ValidArgsFunction: func(
+		cmd *cobra.Command,
+		args []string,
+		toComplete string,
+	) ([]string, cobra.ShellCompDirective) {
+		matchingVersions, directive := clog.CompleteReleasesAsFirstArgument(cmd, args, toComplete)
+		if matchingVersions == nil {
+			return matchingVersions, directive
+		}
+
+		// We also support 'latest' as an alias
+		matchingVersions = append(matchingVersions, "latest")
+		matchingVersions = append(matchingVersions, "next")
+		matchingVersions = append(matchingVersions, "unreleased")
+
+		return matchingVersions, cobra.ShellCompDirectiveNoFileComp
+	},
 	RunE: func(cmd *cobra.Command, args []string) error {
 		path, err := clog.ResolvePathToChangelog()
 		if err != nil {
@@ -27,12 +51,30 @@ var showCmd = &cobra.Command{
 			return err
 		}
 
+		if len(args) == 0 {
+			if shouldShowPlain {
+				fmt.Print(string(source))
+				return nil
+			}
+
+			return clog.Show(string(source))
+		}
+
+		changelog := clog.Parse(source)
+		// TODO: These bounds are always off by two (too much) at the Stop
+		bounds, err := findReleaseBounds(args[0], &changelog)
+		if err != nil {
+			return err
+		}
+
+		contents := changelog.ContentWithin(bounds)
+
 		if shouldShowPlain {
-			fmt.Print(string(source))
+			fmt.Print(contents)
 			return nil
 		}
 
-		return clog.Show(string(source))
+		return clog.Show(contents)
 	},
 }
 
@@ -51,3 +93,51 @@ func init() {
 	// is called directly, e.g.:
 	// showCmd.Flags().BoolP("toggle", "t", false, "Help message for toggle")
 }
+
+func isAlias(alias string) bool {
+	versionAliases := []string{
+		"latest",
+		"next",
+		"unreleased",
+	}
+	for _, knownAlias := range versionAliases {
+		if alias == knownAlias {
+			return true
+		}
+	}
+
+	return false
+}
+
+func findReleaseBounds(versionOrAlias string, changelog *clog.Changelog) (*clog.Bounds, error) {
+	if isAlias(versionOrAlias) {
+		alias := versionOrAlias
+
+		if alias == "latest" {
+			if len(changelog.Releases.Past) < 1 {
+				return nil, fmt.Errorf("Cannot show latest release, since there are none")
+			}
+
+			return &changelog.Releases.Past[0].Bounds, nil
+		}
+
+		if alias == "next" || alias == "unreleased" {
+			nextRelease := changelog.Releases.Next
+			if nextRelease == nil {
+				return nil, fmt.Errorf("Cannot show next release, since there is none")
+			}
+
+			return &nextRelease.Bounds, nil
+		}
+
+		return nil, fmt.Errorf("Unknown version or alias '%s'")
+	}
+
+	version := versionOrAlias
+	release := changelog.FindRelease(version)
+	if release == nil {
+		return nil, fmt.Errorf("Release '%s' not found", version)
+	}
+
+	return &release.Bounds, nil
+}

cmd/yank.go

@@ -3,6 +3,7 @@ package cmd
 import (
 	"fmt"
 	"os"
+	"strings"
 
 	"github.com/spf13/cobra"
 
@@ -11,11 +12,33 @@ import (
 
 // yankCmd represents the yank command
 var yankCmd = &cobra.Command{
-	Use:               "yank",
-	Short:             "Marks the specified release as yanked",
-	Long:              `As described by https://keepachangelog.com, yanked releases are versions that had to be pulled because of a serious bug or security issue.`,
-	Args:              cobra.ExactArgs(1),
-	ValidArgsFunction: clog.CompleteReleasesAsFirstArgument,
+	Use:   "yank",
+	Short: "Marks the specified release as yanked",
+	Long:  `As described by https://keepachangelog.com, yanked releases are versions that had to be pulled because of a serious bug or security issue.`,
+	Args:  cobra.ExactArgs(1),
+	ValidArgsFunction: func(
+		cmd *cobra.Command,
+		args []string,
+		toComplete string,
+	) ([]string, cobra.ShellCompDirective) {
+		if len(args) != 0 {
+			return nil, cobra.ShellCompDirectiveNoFileComp
+		}
+
+		changelog, _, err := clog.ResolveChangelog()
+		if err != nil {
+			return nil, cobra.ShellCompDirectiveNoFileComp
+		}
+
+		matchingVersions := make([]string, 0)
+		for _, release := range changelog.Releases.Past {
+			if !release.Yanked && strings.HasPrefix(release.Version, toComplete) {
+				matchingVersions = append(matchingVersions, release.Version)
+			}
+		}
+
+		return matchingVersions, cobra.ShellCompDirectiveNoFileComp
+	},
 	RunE: func(cmd *cobra.Command, args []string) error {
 		changelog, changelogPath, err := clog.ResolveChangelog()
 		if err != nil {

internal/changelog/completions.go

@@ -8,7 +8,11 @@ import (
 
 // Can be passed as ValidArgsFunction to support custom completions if the
 // first argument is a released version.
-func CompleteReleasesAsFirstArgument(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+func CompleteReleasesAsFirstArgument(
+	cmd *cobra.Command,
+	args []string,
+	toComplete string,
+) ([]string, cobra.ShellCompDirective) {
 	if len(args) != 0 {
 		return nil, cobra.ShellCompDirectiveNoFileComp
 	}

internal/changelog/show.go

@@ -6,6 +6,10 @@ import (
 	"github.com/charmbracelet/glamour"
 )
 
+func (changelog *Changelog) ContentWithin(bounds *Bounds) string {
+	return changelog.source[bounds.Start:bounds.Stop]
+}
+
 func Show(contents string) error {
 	renderer, _ := glamour.NewTermRenderer(
 		// detect background color and pick either the default dark or light theme