Add bash completion

pkg/auxents/auxents.go

@@ -31,6 +31,7 @@ func init() {
 		{"lecat", lecatMain},
 		{"termcvt", termcvtMain},
 		{"unhex", unhexMain},
+		{"completion", genCompletion},
 	}
 }
 

pkg/auxents/completion.go

@@ -0,0 +1,35 @@
+package auxents
+
+import "fmt"
+
+func genCompletion(args []string) int {
+	verb := args[1]
+	args = args[2:]
+
+	printUsage := func() {
+		fmt.Printf("Usage: mlr %s SHELL\n", verb)
+		fmt.Println("Supported shells: bash")
+		fmt.Println()
+		fmt.Println("Add below to your bashrc to enable completion")
+		fmt.Println("source <(mlr completion bash)")
+	}
+
+	if len(args) != 1 {
+		printUsage()
+		return 1
+	}
+
+	if args[0] == "-h" || args[0] == "--help" {
+		printUsage()
+		return 0
+	}
+
+	if args[0] != "bash" {
+		fmt.Printlf("Unsupported shell: %s\n", args[0])
+		printUsage()
+		return 1
+	}
+
+	fmt.Println(`complete -o nospace -o nosort -C "mlr _complete_bash" mlr`)
+	return 0
+}

pkg/completion/completion.go

@@ -0,0 +1,65 @@
+// Package completion handles Shell completion
+package completion
+
+import (
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+
+	"github.com/johnkerl/miller/v6/pkg/transformers"
+)
+
+func DoCompletion() {
+	if os.Args[1] != "_complete_bash" {
+		return
+	}
+	if len(os.Args) < 5 {
+		Debug()
+		return
+	}
+	// See: https://www.gnu.org/software/bash/manual/html_node/Programmable-Completion-Builtins.html#index-complete
+	// Bash completion calls with three arguments: $1 is the name of the
+	// command whose arguments are being completed, $2 is the word being
+	// completed, and $3 is the word preceding the word being completed. Since
+	// we already set one argument, the rest of them are shifted by one
+	// position i.e.  `mlr _complete_bash <mlr> <last> <prev>`,
+	last := os.Args[3]
+	prev := os.Args[4]
+	if prev == "then" {
+		matches := GetMatchingVerbs(last)
+		// See: https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html#index-COMP_005fTYPE
+		// When tab is hit two times, bash sets COMP_TYPE to ascii value of `?` i.e. 63
+		if len(matches) == 1 && matches[0].Verb == last && os.Getenv("COMP_TYPE") == "63" {
+			v := matches[0]
+			v.UsageFunc(os.Stdout)
+		} else {
+			sort.Slice(matches, func(i, j int) bool { return matches[i].Verb < matches[j].Verb })
+			for _, verb := range matches {
+				fmt.Println(verb.Verb)
+			}
+		}
+	}
+}
+
+func GetMatchingVerbs(partVerb string) []*transformers.TransformerSetup {
+	var matches []*transformers.TransformerSetup
+	for _, verb := range transformers.TRANSFORMER_LOOKUP_TABLE {
+		localv := verb
+		if strings.HasPrefix(verb.Verb, partVerb) {
+			matches = append(matches, &localv)
+		}
+	}
+	return matches
+}
+
+func Debug() {
+	for i, arg := range os.Args {
+		fmt.Fprintln(os.Stderr, i, arg)
+	}
+	for _, val := range os.Environ() {
+		if strings.HasPrefix(val, "COMP") {
+			fmt.Fprintln(os.Stderr, val)
+		}
+	}
+}

pkg/entrypoint/entrypoint.go

@@ -9,10 +9,12 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"strings"
 
 	"github.com/johnkerl/miller/v6/pkg/auxents"
 	"github.com/johnkerl/miller/v6/pkg/cli"
 	"github.com/johnkerl/miller/v6/pkg/climain"
+	"github.com/johnkerl/miller/v6/pkg/completion"
 	"github.com/johnkerl/miller/v6/pkg/lib"
 	"github.com/johnkerl/miller/v6/pkg/platform"
 	"github.com/johnkerl/miller/v6/pkg/stream"
@@ -24,6 +26,13 @@ type MainReturn struct {
 }
 
 func Main() MainReturn {
+
+	if len(os.Args) > 1 {
+		if strings.HasPrefix(os.Args[1], "_complete") {
+			completion.DoCompletion()
+			return MainReturn{PrintElapsedTime: false}
+		}
+	}
 	// Special handling for Windows so we can do things like:
 	//
 	//   mlr put '$a = $b . "cd \"efg\" hi"' foo.dat