port over shell completion w/ cobra from grype, find/replace, etc.

Signed-off-by: Samuel Dacanay <sam.dacanay@anchore.com>

cmd/completion.go

@@ -0,0 +1,65 @@
+package cmd
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+// completionCmd represents the completion command
+var completionCmd = &cobra.Command{
+	Use:   "completion [bash|zsh|fish]",
+	Short: "Generate a shell completion for Syft (listing local docker images)",
+	Long: `To load completions (docker image list):
+
+Bash:
+
+$ source <(syft completion bash)
+
+# To load completions for each session, execute once:
+Linux:
+  $ syft completion bash > /etc/bash_completion.d/syft
+MacOS:
+  $ syft completion bash > /usr/local/etc/bash_completion.d/syft
+
+Zsh:
+
+# If shell completion is not already enabled in your environment you will need
+# to enable it.  You can execute the following once:
+
+$ echo "autoload -U compinit; compinit" >> ~/.zshrc
+
+# To load completions for each session, execute once:
+$ syft completion zsh > "${fpath[1]}/_syft"
+
+# You will need to start a new shell for this setup to take effect.
+
+Fish:
+
+$ syft completion fish | source
+
+# To load completions for each session, execute once:
+$ syft completion fish > ~/.config/fish/completions/syft.fish
+`,
+	DisableFlagsInUseLine: true,
+	ValidArgs:             []string{"bash", "zsh", "fish"},
+	Args:                  cobra.ExactValidArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		var err error
+		switch args[0] {
+		case "bash":
+			err = cmd.Root().GenBashCompletion(os.Stdout)
+		case "zsh":
+			err = cmd.Root().GenZshCompletion(os.Stdout)
+		case "fish":
+			err = cmd.Root().GenFishCompletion(os.Stdout, true)
+		}
+		if err != nil {
+			panic(err)
+		}
+	},
+}
+
+func init() {
+	rootCmd.AddCommand(completionCmd)
+}

cmd/root.go

@@ -1,8 +1,14 @@
 package cmd
 
 import (
+	"context"
 	"fmt"
 	"os"
+	"strings"
+
+	"github.com/docker/docker/api/types"
+	"github.com/docker/docker/api/types/filters"
+	"github.com/docker/docker/client"
 
 	"github.com/anchore/syft/internal"
 	"github.com/anchore/syft/internal/bus"
@@ -44,6 +50,20 @@ Supports the following image sources:
 			os.Exit(1)
 		}
 	},
+	ValidArgsFunction: func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+		// Since we use ValidArgsFunction, Cobra will call this AFTER having parsed all flags and arguments provided
+		dockerImageRepoTags, err := ListLocalDockerImages(toComplete)
+		if err != nil {
+			// Indicates that an error occurred and completions should be ignored
+			return []string{"completion failed"}, cobra.ShellCompDirectiveError
+		}
+		if len(dockerImageRepoTags) == 0 {
+			return []string{"no docker images found"}, cobra.ShellCompDirectiveError
+		}
+		// ShellCompDirectiveDefault indicates that the shell will perform its default behavior after completions have
+		// been provided (without implying other possible directives)
+		return dockerImageRepoTags, cobra.ShellCompDirectiveDefault
+	},
 }
 
 func startWorker(userInput string) <-chan error {
@@ -88,3 +108,30 @@ func doRunCmd(_ *cobra.Command, args []string) error {
 	ux := ui.Select(appConfig.CliOptions.Verbosity > 0, appConfig.Quiet)
 	return ux(errs, eventSubscription)
 }
+
+func ListLocalDockerImages(prefix string) ([]string, error) {
+	var repoTags = make([]string, 0)
+	ctx := context.Background()
+	cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
+	if err != nil {
+		return repoTags, err
+	}
+
+	// Only want to return tagged images
+	imageListArgs := filters.NewArgs()
+	imageListArgs.Add("dangling", "false")
+	images, err := cli.ImageList(ctx, types.ImageListOptions{All: false, Filters: imageListArgs})
+	if err != nil {
+		return repoTags, err
+	}
+
+	for _, image := range images {
+		// image may have multiple tags
+		for _, tag := range image.RepoTags {
+			if strings.HasPrefix(tag, prefix) {
+				repoTags = append(repoTags, tag)
+			}
+		}
+	}
+	return repoTags, nil
+}