devbox: add AppendScript method to ConfigShellCmds (#149)

This method takes a script as a string and appends it to the slice of
shell commands in the config. From the docs:

	AppendScript appends each line of a script to s.Cmds. It also
	applies the following formatting rules:

	  - Trim leading newlines from the script.
	  - Trim trailing whitespace from the script.
- If the first line of the script begins with one or more tabs ('\t'),
then unindent each line by that same number of tabs.
	  - Remove trailing whitespace from each line.

	Note that unindenting only happens when a line starts with at
	least as many tabs as the first line. If it starts with
	fewer tabs, then it is not unindented at all.

See `config_test.go` for an example.

config.go

@@ -7,6 +7,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"strings"
+	"unicode"
 
 	"github.com/pkg/errors"
 	"go.jetpack.io/devbox/cuecfg"
@@ -93,6 +94,33 @@ type ConfigShellCmds struct {
 	Cmds      []string
 }
 
+// AppendScript appends each line of a script to s.Cmds. It also applies the
+// following formatting rules:
+//
+//   - Trim leading newlines from the script.
+//   - Trim trailing whitespace from the script.
+//   - If the first line of the script begins with one or more tabs ('\t'), then
+//     unindent each line by that same number of tabs.
+//   - Remove trailing whitespace from each line.
+//
+// Note that unindenting only happens when a line starts with at least as many
+// tabs as the first line. If it starts with fewer tabs, then it is not
+// unindented at all.
+func (s *ConfigShellCmds) AppendScript(script string) {
+	script = strings.TrimLeft(script, "\r\n ")
+	script = strings.TrimRightFunc(script, unicode.IsSpace)
+	if len(script) == 0 {
+		return
+	}
+	prefixLen := strings.IndexFunc(script, func(r rune) bool { return r != '\t' })
+	prefix := strings.Repeat("\t", prefixLen)
+	for _, line := range strings.Split(script, "\n") {
+		line = strings.TrimRightFunc(line, unicode.IsSpace)
+		line = strings.TrimPrefix(line, prefix)
+		s.Cmds = append(s.Cmds, line)
+	}
+}
+
 // MarshalJSON marshals shell commands according to s.MarshalAs. It marshals
 // commands to a string by joining s.Cmds with newlines.
 func (s ConfigShellCmds) MarshalJSON() ([]byte, error) {

config_test.go

@@ -2,6 +2,7 @@ package devbox
 
 import (
 	"encoding/json"
+	"fmt"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -145,3 +146,106 @@ func TestConfigShellCmdsString(t *testing.T) {
 		})
 	}
 }
+
+func ExampleConfigShellCmds_AppendScript() {
+	shCmds := ConfigShellCmds{}
+	shCmds.AppendScript(`
+		# This script will be unindented by the number of leading tabs
+		# on the first line.
+		if true; then
+			echo "this is always printed"
+		fi`,
+	)
+	b, _ := json.MarshalIndent(&shCmds, "", "  ")
+	fmt.Println(string(b))
+
+	// Output:
+	// [
+	//   "# This script will be unindented by the number of leading tabs",
+	//   "# on the first line.",
+	//   "if true; then",
+	//   "\techo \"this is always printed\"",
+	//   "fi"
+	// ]
+}
+
+func TestAppendScript(t *testing.T) {
+	tests := []struct {
+		name     string
+		script   string
+		wantCmds []string
+	}{
+		{
+			name:     "Empty",
+			script:   "",
+			wantCmds: nil,
+		},
+		{
+			name:     "OnlySpaces",
+			script:   " ",
+			wantCmds: nil,
+		},
+		{
+			name:     "Only newlines",
+			script:   "\r\n",
+			wantCmds: nil,
+		},
+		{
+			name:     "Simple",
+			script:   "echo test",
+			wantCmds: []string{"echo test"},
+		},
+		{
+			name:     "LeadingNewline",
+			script:   "\necho test",
+			wantCmds: []string{"echo test"},
+		},
+		{
+			name:     "LeadingNewlineAndSpace",
+			script:   "\n    echo test",
+			wantCmds: []string{"echo test"},
+		},
+		{
+			name:     "TrailingWhitespace",
+			script:   "echo test  \n",
+			wantCmds: []string{"echo test"},
+		},
+		{
+			name:   "SecondLineIndent",
+			script: "if true; then\n\techo test\nfi",
+			wantCmds: []string{
+				"if true; then",
+				"\techo test",
+				"fi",
+			},
+		},
+		{
+			name:   "Unindent",
+			script: "\n\tif true; then\n\t\techo test\n\tfi",
+			wantCmds: []string{
+				"if true; then",
+				"\techo test",
+				"fi",
+			},
+		},
+		{
+			name:   "UnindentTooFewTabs",
+			script: "\t\tif true; then\n\techo test\n\t\tfi",
+			wantCmds: []string{
+				"if true; then",
+				"\techo test",
+				"fi",
+			},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			shCmds := ConfigShellCmds{}
+			shCmds.AppendScript(test.script)
+			gotCmds := shCmds.Cmds
+			if diff := cmp.Diff(test.wantCmds, gotCmds); diff != "" {
+				t.Errorf("Got incorrect commands slice (-want +got):\n%s", diff)
+			}
+		})
+	}
+}