chore(lint): enable additional golangci-lint rules and fix all findings (#46)

Enable 10 new linters in `.golangci.yml`: `copyloopvar`, `dupword`,
`errname`, `errorlint`, `gocritic`, `intrange`, `modernize`,
`nilerr`, `perfsprint`, and `unconvert`.

Fixes across 19 files:

- Use `errors.Is`/`errors.As` instead of `==`/type assertions on errors
- Use `errors.New` instead of `fmt.Errorf` for static error strings
- Use `any` instead of `interface{}`, `strings.SplitSeq` instead of
  `strings.Split`, `slices.Contains` instead of manual loop
- Convert if-else chains to switch statements
- Use integer range loops (`for i := range n`)
- Rename `gitPathErr` to `errGitPath` per sentinel error convention
- Suppress `nilerr` for intentional patterns (git exit codes as booleans)

Author: boneskull

.golangci.yml

@@ -5,12 +5,22 @@ run:
 
 linters:
   enable:
+    - copyloopvar
+    - dupword
     - errcheck
+    - errname
+    - errorlint
+    - gocritic
     - govet
-    - staticcheck
-    - unused
     - ineffassign
+    - intrange
     - misspell
+    - modernize
+    - nilerr
+    - perfsprint
+    - staticcheck
+    - unconvert
+    - unused
     # gosec disabled - false positives for CLI tools that shell out to git
   settings:
     errcheck:

cmd/abort.go

@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -35,7 +36,7 @@ func runAbort(cmd *cobra.Command, args []string) error {
 	// Check if cascade in progress
 	st, err := state.Load(g.GetGitDir())
 	if err != nil {
-		return fmt.Errorf("no operation in progress")
+		return errors.New("no operation in progress")
 	}
 
 	// Abort rebase if in progress

cmd/adopt.go

@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -88,7 +89,7 @@ func runAdopt(cmd *cobra.Command, args []string) error {
 	if parentNode != nil {
 		for _, ancestor := range tree.GetAncestors(parentNode) {
 			if ancestor.Name == branchName {
-				return fmt.Errorf("cannot adopt: would create a cycle")
+				return errors.New("cannot adopt: would create a cycle")
 			}
 		}
 	}

cmd/cascade.go

@@ -54,7 +54,7 @@ func runCascade(cmd *cobra.Command, args []string) error {
 
 	// Check if cascade already in progress
 	if state.Exists(g.GetGitDir()) {
-		return fmt.Errorf("operation already in progress; use 'gh stack continue' or 'gh stack abort'")
+		return errors.New("operation already in progress; use 'gh stack continue' or 'gh stack abort'")
 	}
 
 	currentBranch, err := g.CurrentBranch()
@@ -94,7 +94,7 @@ func runCascade(cmd *cobra.Command, args []string) error {
 	err = doCascadeWithState(g, cfg, branches, cascadeDryRunFlag, state.OperationCascade, false, false, false, nil, stashRef, s)
 
 	// Restore auto-stashed changes after operation (unless conflict, which saves stash in state)
-	if stashRef != "" && err != ErrConflict {
+	if stashRef != "" && !errors.Is(err, ErrConflict) {
 		fmt.Println("Restoring auto-stashed changes...")
 		if popErr := g.StashPop(stashRef); popErr != nil {
 			fmt.Printf("%s could not restore stashed changes (commit %s): %v\n", s.WarningIcon(), git.AbbrevSHA(stashRef), popErr)

cmd/continue.go

@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -37,14 +38,14 @@ func runContinue(cmd *cobra.Command, args []string) error {
 	// Check if operation in progress
 	st, err := state.Load(g.GetGitDir())
 	if err != nil {
-		return fmt.Errorf("no operation in progress")
+		return errors.New("no operation in progress")
 	}
 
 	// Complete the in-progress rebase
 	if g.IsRebaseInProgress() {
 		fmt.Println("Continuing rebase...")
 		if rebaseErr := g.RebaseContinue(); rebaseErr != nil {
-			return fmt.Errorf("rebase --continue failed; resolve conflicts first")
+			return errors.New("rebase --continue failed; resolve conflicts first")
 		}
 	}
 
@@ -75,7 +76,7 @@ func runContinue(cmd *cobra.Command, args []string) error {
 
 		if cascadeErr := doCascadeWithState(g, cfg, branches, false, st.Operation, st.UpdateOnly, st.Web, st.PushOnly, st.Branches, st.StashRef, s); cascadeErr != nil {
 			// Stash handling is done by doCascadeWithState (conflict saves in state, errors restore)
-			if cascadeErr != ErrConflict && st.StashRef != "" {
+			if !errors.Is(cascadeErr, ErrConflict) && st.StashRef != "" {
 				fmt.Println("Restoring auto-stashed changes...")
 				if popErr := g.StashPop(st.StashRef); popErr != nil {
 					fmt.Printf("%s could not restore stashed changes (commit %s): %v\n", s.WarningIcon(), git.AbbrevSHA(st.StashRef), popErr)

cmd/create.go

@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -76,7 +77,7 @@ func runCreate(cmd *cobra.Command, args []string) error {
 
 	if hasStaged && !createEmptyFlag {
 		if createMessageFlag == "" {
-			return fmt.Errorf("staged changes found but no commit message provided; use -m or --empty")
+			return errors.New("staged changes found but no commit message provided; use -m or --empty")
 		}
 	}
 

cmd/init.go

@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 
@@ -42,12 +43,13 @@ func runInit(cmd *cobra.Command, args []string) error {
 	trunk := trunkFlag
 	if trunk == "" {
 		// Try main, then master
-		if g.BranchExists("main") {
+		switch {
+		case g.BranchExists("main"):
 			trunk = "main"
-		} else if g.BranchExists("master") {
+		case g.BranchExists("master"):
 			trunk = "master"
-		} else {
-			return fmt.Errorf("could not determine trunk branch; use --trunk to specify")
+		default:
+			return errors.New("could not determine trunk branch; use --trunk to specify")
 		}
 	}
 

cmd/log_test.go

@@ -98,6 +98,7 @@ func TestLogMultipleBranches(t *testing.T) {
 
 	if featureA == nil {
 		t.Fatal("feature-a not found")
+		return
 	}
 
 	if len(featureA.Children) != 1 {

cmd/submit.go

@@ -2,6 +2,7 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"regexp"
@@ -63,10 +64,10 @@ func runSubmit(cmd *cobra.Command, args []string) error {
 
 	// Validate flag combinations
 	if submitPushOnlyFlag && submitUpdateOnlyFlag {
-		return fmt.Errorf("--push-only and --update-only cannot be used together: --push-only skips all PR operations")
+		return errors.New("--push-only and --update-only cannot be used together: --push-only skips all PR operations")
 	}
 	if submitPushOnlyFlag && submitWebFlag {
-		return fmt.Errorf("--push-only and --web cannot be used together: --push-only skips all PR operations")
+		return errors.New("--push-only and --web cannot be used together: --push-only skips all PR operations")
 	}
 	if submitFromFlag != "" && submitCurrentOnlyFlag {
 		return fmt.Errorf("--from and --current-only cannot be used together")
@@ -86,7 +87,7 @@ func runSubmit(cmd *cobra.Command, args []string) error {
 
 	// Check if operation already in progress
 	if state.Exists(g.GetGitDir()) {
-		return fmt.Errorf("operation already in progress; use 'gh stack continue' or 'gh stack abort'")
+		return errors.New("operation already in progress; use 'gh stack continue' or 'gh stack abort'")
 	}
 
 	currentBranch, err := g.CurrentBranch()
@@ -174,7 +175,7 @@ func runSubmit(cmd *cobra.Command, args []string) error {
 	fmt.Println(s.Bold("=== Phase 1: Restack ==="))
 	if cascadeErr := doCascadeWithState(g, cfg, branches, submitDryRunFlag, state.OperationSubmit, submitUpdateOnlyFlag, submitWebFlag, submitPushOnlyFlag, branchNames, stashRef, s); cascadeErr != nil {
 		// Stash is saved in state for conflicts; restore on other errors
-		if cascadeErr != ErrConflict && stashRef != "" {
+		if !errors.Is(cascadeErr, ErrConflict) && stashRef != "" {
 			fmt.Println("Restoring auto-stashed changes...")
 			if popErr := g.StashPop(stashRef); popErr != nil {
 				fmt.Printf("%s could not restore stashed changes (commit %s): %v\n", s.WarningIcon(), git.AbbrevSHA(stashRef), popErr)
@@ -266,7 +267,8 @@ func doSubmitPRs(g *git.Git, cfg *config.Config, root *tree.Node, branches []*tr
 
 		existingPR, _ := cfg.GetPR(b.Name) //nolint:errcheck // 0 is fine
 
-		if existingPR > 0 {
+		switch {
+		case existingPR > 0:
 			// Update existing PR
 			if dryRun {
 				fmt.Printf("%s Would update PR #%d base to %s\n", s.Muted("dry-run:"), existingPR, s.Branch(parent))
@@ -289,27 +291,28 @@ func doSubmitPRs(g *git.Git, cfg *config.Config, root *tree.Node, branches []*tr
 				// If PR is a draft and now targets trunk, offer to publish
 				maybeMarkPRReady(ghClient, existingPR, b.Name, parent, trunk, s)
 			}
-		} else if !updateOnly {
+		case !updateOnly:
 			// Create new PR
 			if dryRun {
 				fmt.Printf("%s Would create PR for %s (base: %s)\n", s.Muted("dry-run:"), s.Branch(b.Name), s.Branch(parent))
 			} else {
 				prNum, adopted, err := createPRForBranch(g, ghClient, cfg, root, b.Name, parent, trunk, remoteBranches, s)
-				if err != nil {
+				switch {
+				case err != nil:
 					fmt.Printf("%s failed to create PR for %s: %v\n", s.WarningIcon(), s.Branch(b.Name), err)
-				} else if adopted {
+				case adopted:
 					fmt.Printf("%s Adopted PR #%d for %s (%s)\n", s.SuccessIcon(), prNum, s.Branch(b.Name), ghClient.PRURL(prNum))
 					if openWeb {
 						prURLs = append(prURLs, ghClient.PRURL(prNum))
 					}
-				} else {
+				default:
 					fmt.Printf("%s Created PR #%d for %s (%s)\n", s.SuccessIcon(), prNum, s.Branch(b.Name), ghClient.PRURL(prNum))
 					if openWeb {
 						prURLs = append(prURLs, ghClient.PRURL(prNum))
 					}
 				}
 			}
-		} else {
+		default:
 			fmt.Printf("Skipping %s %s\n", s.Branch(b.Name), s.Muted("(no existing PR, --update-only)"))
 		}
 	}
@@ -447,7 +450,7 @@ func promptForPRDetails(branch, defaultTitle, defaultBody string, s *style.Style
 	}
 	title = strings.TrimSpace(title)
 	if title == "" {
-		return "", "", fmt.Errorf("PR title cannot be empty")
+		return "", "", errors.New("PR title cannot be empty")
 	}
 
 	// Show the generated body and ask if user wants to edit

cmd/sync.go

@@ -2,8 +2,10 @@
 package cmd
 
 import (
+	"errors"
 	"fmt"
 	"os"
+	"slices"
 
 	"github.com/boneskull/gh-stack/internal/config"
 	"github.com/boneskull/gh-stack/internal/git"
@@ -184,7 +186,7 @@ func runSync(cmd *cobra.Command, args []string) error {
 	// Uses git diff to detect when a branch's content is already in trunk
 	for _, branch := range branches {
 		// Skip already detected via PR
-		if sliceContains(merged, branch) {
+		if slices.Contains(merged, branch) {
 			continue
 		}
 
@@ -215,7 +217,7 @@ func runSync(cmd *cobra.Command, args []string) error {
 		}
 
 		// Skip if parent is already marked as merged (will be handled)
-		if sliceContains(merged, parent) {
+		if slices.Contains(merged, parent) {
 			continue
 		}
 
@@ -351,7 +353,7 @@ func runSync(cmd *cobra.Command, args []string) error {
 			allBranches := []*tree.Node{child}
 			allBranches = append(allBranches, tree.GetDescendants(child)...)
 			if err := doCascadeWithState(g, cfg, allBranches, syncDryRunFlag, state.OperationCascade, false, false, false, nil, stashRef, s); err != nil {
-				if err == ErrConflict {
+				if errors.Is(err, ErrConflict) {
 					hitConflict = true
 				}
 				return err
@@ -373,16 +375,6 @@ func runSync(cmd *cobra.Command, args []string) error {
 	return nil
 }
 
-// sliceContains returns true if slice contains the given string.
-func sliceContains(slice []string, s string) bool {
-	for _, item := range slice {
-		if item == s {
-			return true
-		}
-	}
-	return false
-}
-
 // mergedAction represents the user's choice for handling a merged branch.
 type mergedAction int