consolidated prefix input and validation

cmd/init.go

@@ -108,6 +108,49 @@ func runInit(cfg *config.Config, opts *initOptions) error {
 		return ErrInvalidArgs
 	}
 
+	// Prompt for prefix interactively if not provided via flag and we're
+	// in interactive mode (not adopt, not explicit branches).
+	if opts.prefix == "" && !opts.adopt && len(opts.branches) == 0 && cfg.IsInteractive() {
+		p := prompter.New(cfg.In, cfg.Out, cfg.Err)
+		if opts.numbered {
+			// --numbered requires a prefix; prompt specifically for one
+			prefixInput, err := p.Input("Enter a branch prefix (required for --numbered)", "")
+			if err != nil {
+				if isInterruptError(err) {
+					printInterrupt(cfg)
+					return ErrSilent
+				}
+				cfg.Errorf("failed to read prefix: %s", err)
+				return ErrSilent
+			}
+			opts.prefix = strings.TrimSpace(prefixInput)
+			if opts.prefix == "" {
+				cfg.Errorf("--numbered requires a prefix")
+				return ErrInvalidArgs
+			}
+		} else {
+			prefixInput, err := p.Input("Set a branch prefix? (leave blank to skip)", "")
+			if err != nil {
+				if isInterruptError(err) {
+					printInterrupt(cfg)
+					return ErrSilent
+				}
+				cfg.Errorf("failed to read prefix: %s", err)
+				return ErrSilent
+			}
+			opts.prefix = strings.TrimSpace(prefixInput)
+		}
+	}
+
+	// Validate prefix, after it has been determined (from flag or prompt),
+	// before any branch creation.
+	if opts.prefix != "" {
+		if err := git.ValidateRefName(opts.prefix); err != nil {
+			cfg.Errorf("invalid prefix %q: must be a valid git ref component", opts.prefix)
+			return ErrInvalidArgs
+		}
+	}
+
 	if opts.adopt {
 		// Adopt mode: validate all specified branches exist
 		if len(opts.branches) == 0 {
@@ -165,46 +208,13 @@ func runInit(cfg *config.Config, opts *initOptions) error {
 		}
 		branches = prefixed
 	} else {
-		// Interactive mode
+		// Interactive mode — prefix was already prompted for above
 		if !cfg.IsInteractive() {
 			cfg.Errorf("interactive input required; provide branch names or use --adopt")
 			return ErrInvalidArgs
 		}
 		p := prompter.New(cfg.In, cfg.Out, cfg.Err)
 
-		// Step 1: Ask for prefix
-		if opts.prefix == "" {
-			if opts.numbered {
-				// --numbered requires a prefix; prompt specifically for one
-				prefixInput, err := p.Input("Enter a branch prefix (required for --numbered)", "")
-				if err != nil {
-					if isInterruptError(err) {
-						printInterrupt(cfg)
-						return ErrSilent
-					}
-					cfg.Errorf("failed to read prefix: %s", err)
-					return ErrSilent
-				}
-				opts.prefix = strings.TrimSpace(prefixInput)
-				if opts.prefix == "" {
-					cfg.Errorf("--numbered requires a prefix")
-					return ErrInvalidArgs
-				}
-			} else {
-				prefixInput, err := p.Input("Set a branch prefix? (leave blank to skip)", "")
-				if err != nil {
-					if isInterruptError(err) {
-						printInterrupt(cfg)
-						return ErrSilent
-					}
-					cfg.Errorf("failed to read prefix: %s", err)
-					return ErrSilent
-				}
-				opts.prefix = strings.TrimSpace(prefixInput)
-			}
-		}
-
-		// Step 2: Ask for branch name (unless --numbered auto-generates it)
 		if opts.numbered {
 			// Auto-generate numbered branch name
 			branchName := branch.NextNumberedName(opts.prefix, nil)
@@ -283,14 +293,6 @@ func runInit(cfg *config.Config, opts *initOptions) error {
 		}
 	}
 
-	// Validate prefix (from flag or interactive input)
-	if opts.prefix != "" {
-		if err := git.ValidateRefName(opts.prefix); err != nil {
-			cfg.Errorf("invalid prefix %q: must be a valid git ref component", opts.prefix)
-			return ErrInvalidArgs
-		}
-	}
-
 	// Build stack
 	trunkSHA, _ := git.RevParse(trunk)
 	branchRefs := make([]stack.BranchRef, len(branches))

cmd/init_test.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"fmt"
 	"io"
 	"os"
 	"testing"
@@ -137,6 +138,32 @@ func TestInit_PrefixAppliedToExplicitBranches(t *testing.T) {
 	assert.Equal(t, []string{"feat/b1", "feat/b2"}, names, "stack should store prefixed branch names")
 }
 
+func TestInit_InvalidPrefixRejectedBeforeBranchCreation(t *testing.T) {
+	gitDir := t.TempDir()
+	var created []string
+	restore := git.SetOps(&git.MockOps{
+		GitDirFn:        func() (string, error) { return gitDir, nil },
+		DefaultBranchFn: func() (string, error) { return "main", nil },
+		CurrentBranchFn: func() (string, error) { return "main", nil },
+		ValidateRefNameFn: func(name string) error {
+			return fmt.Errorf("invalid ref name: %s", name)
+		},
+		CreateBranchFn: func(name, base string) error {
+			created = append(created, name)
+			return nil
+		},
+	})
+	defer restore()
+
+	cfg, outR, errR := config.NewTestConfig()
+	err := runInit(cfg, &initOptions{branches: []string{"mybranch"}, prefix: "bad..prefix"})
+	output := collectOutput(cfg, outR, errR)
+
+	assert.ErrorIs(t, err, ErrInvalidArgs, "should reject invalid prefix")
+	assert.Contains(t, output, "invalid prefix")
+	assert.Empty(t, created, "no branches should be created when prefix is invalid")
+}
+
 func TestInit_RerereAlreadyEnabled(t *testing.T) {
 	gitDir := t.TempDir()
 	enableRerereCalled := false