feat: Add auto-fix with import management (#179)

## Description

- enhance `format-with-verb` rule with context-specific suggestions and
auto-fix support
- Add automatic import management (add missing, remove unused) after
applying fixes
- Add `RequiredImports` field to `Issue` type to track imports needed
for fixes

### Import Processing

- Add `ProcessImports` function
- Automatically add required imports (e.g. `errors` package when
replacing `ufmt.Errorf`)
- Support `*.gno` files by treating them as `*.go` for import solution

Author: notJoon

.gitignore

@@ -20,3 +20,5 @@
 # Go workspace file
 go.work
 go.work.sum
+
+.gocache

internal/fixer/fixer.go

@@ -3,9 +3,6 @@ package fixer
 import (
 	"bytes"
 	"fmt"
-	"go/format"
-	"go/parser"
-	"go/token"
 	"os"
 	"sort"
 	"strings"
@@ -114,18 +111,15 @@ func (f *Fixer) writeFixedContent(filename string, lines []string) error {
 		}
 	}
 
-	fset := token.NewFileSet()
-	astFile, err := parser.ParseFile(fset, filename, f.buffer.Bytes(), parser.ParseComments)
+	// Process imports: adds missing imports and removes unused ones
+	content, err := ProcessImports(filename, f.buffer.Bytes())
 	if err != nil {
-		return fmt.Errorf("failed to parse file: %w", err)
+		// If import processing fails, fall back to basic formatting
+		fmt.Printf("Warning: failed to process imports: %v\n", err)
+		content = f.buffer.Bytes()
 	}
 
-	f.buffer.Reset()
-	if err := format.Node(&f.buffer, fset, astFile); err != nil {
-		return fmt.Errorf("failed to format file: %w", err)
-	}
-
-	if err := os.WriteFile(filename, f.buffer.Bytes(), defaultFilePermissions); err != nil {
+	if err := os.WriteFile(filename, content, defaultFilePermissions); err != nil {
 		return fmt.Errorf("failed to write file: %w", err)
 	}
 

internal/fixer/fixer_test.go

@@ -176,6 +176,136 @@ func main() {
 		"oldOwner", oldOwner,
 	)
 }
+`,
+		},
+		{
+			name: "Fix - format-without-verb Errorf with return",
+			input: `package main
+
+func example() error {
+	return ufmt.Errorf("handler error")
+}
+`,
+			issues: []tt.Issue{
+				{
+					Rule:       "format-without-verb",
+					Message:    "format string has no verbs; use errors.New() instead",
+					Start:      token.Position{Line: 4, Column: 9},
+					End:        token.Position{Line: 4, Column: 38},
+					Suggestion: `return errors.New("handler error")`,
+				},
+			},
+			expected: `package main
+
+import "errors"
+
+func example() error {
+	return errors.New("handler error")
+}
+`,
+		},
+		{
+			name: "Fix - format-without-verb Sprintf to literal",
+			input: `package main
+
+func main() {
+	msg := ufmt.Sprintf("hello world")
+}
+`,
+			issues: []tt.Issue{
+				{
+					Rule:       "format-without-verb",
+					Message:    "format string has no verbs; use a string literal directly",
+					Start:      token.Position{Line: 4, Column: 9},
+					End:        token.Position{Line: 4, Column: 37},
+					Suggestion: `msg := "hello world"`,
+				},
+			},
+			expected: `package main
+
+func main() {
+	msg := "hello world"
+}
+`,
+		},
+		{
+			name: "Fix - format-without-verb Printf to print",
+			input: `package main
+
+func main() {
+	ufmt.Printf("status ok")
+}
+`,
+			issues: []tt.Issue{
+				{
+					Rule:       "format-without-verb",
+					Message:    "format string has no verbs; use print() instead",
+					Start:      token.Position{Line: 4, Column: 2},
+					End:        token.Position{Line: 4, Column: 26},
+					Suggestion: `print("status ok")`,
+				},
+			},
+			expected: `package main
+
+func main() {
+	print("status ok")
+}
+`,
+		},
+		{
+			name: "Fix - format-without-verb Errorf adds errors import",
+			input: `package main
+
+func example() error {
+	return ufmt.Errorf("handler error")
+}
+`,
+			issues: []tt.Issue{
+				{
+					Rule:            "format-without-verb",
+					Message:         "format string has no verbs; use errors.New() instead",
+					Start:           token.Position{Line: 4, Column: 9},
+					End:             token.Position{Line: 4, Column: 38},
+					Suggestion:      `return errors.New("handler error")`,
+					RequiredImports: []string{"errors"},
+				},
+			},
+			expected: `package main
+
+import "errors"
+
+func example() error {
+	return errors.New("handler error")
+}
+`,
+		},
+		{
+			name: "Fix - does not duplicate existing import",
+			input: `package main
+
+import "errors"
+
+func example() error {
+	return ufmt.Errorf("handler error")
+}
+`,
+			issues: []tt.Issue{
+				{
+					Rule:            "format-without-verb",
+					Message:         "format string has no verbs; use errors.New() instead",
+					Start:           token.Position{Line: 6, Column: 9},
+					End:             token.Position{Line: 6, Column: 38},
+					Suggestion:      `return errors.New("handler error")`,
+					RequiredImports: []string{"errors"},
+				},
+			},
+			expected: `package main
+
+import "errors"
+
+func example() error {
+	return errors.New("handler error")
+}
 `,
 		},
 	}

internal/fixer/imports.go

@@ -0,0 +1,34 @@
+package fixer
+
+import (
+	"path/filepath"
+	"strings"
+
+	"golang.org/x/tools/imports"
+)
+
+// ProcessImports uses goimports-style processing to:
+//  1. Add missing imports (for standard library packages)
+//  2. Remove unused imports
+//  3. Format the code
+func ProcessImports(filename string, src []byte) ([]byte, error) {
+	// For .gno files, use .go extension so imports package recognizes it
+	processName := filename
+	if strings.HasSuffix(filename, ".gno") {
+		processName = strings.TrimSuffix(filepath.Base(filename), ".gno") + ".go"
+	}
+
+	opts := &imports.Options{
+		Comments:   true,
+		TabIndent:  true,
+		TabWidth:   8,
+		FormatOnly: false, // Process imports, not just format
+	}
+
+	result, err := imports.Process(processName, src, opts)
+	if err != nil {
+		return src, err
+	}
+
+	return result, nil
+}