fix: better errors and import spacing

Signed-off-by: jolheiser <john.olheiser@gmail.com>

format/format.go

@@ -2,13 +2,14 @@ package format
 
 import (
 	"errors"
+	"fmt"
 	"regexp"
 	"strings"
 )
 
 var (
 	importRe     = regexp.MustCompile(`(?ms)import \(([^)]+)\)`)
-	otherRe      = regexp.MustCompile(`(?:var|const|func)\s`)
+	otherRe      = regexp.MustCompile(`^(?:var|const|func)\s`)
 	ErrNoImports = errors.New("no imports found")
 )
 
@@ -16,17 +17,17 @@ var (
 func Source(src []byte, module string) ([]byte, error) {
 	importStart := importRe.FindIndex(src)
 	if importStart == nil {
-		return nil, ErrNoImports
+		return nil, fmt.Errorf("could not find imports: %w", ErrNoImports)
 	}
 
 	otherStart := otherRe.FindIndex(src)
 	if otherStart != nil && otherStart[0] < importStart[0] {
-		return nil, ErrNoImports
+		return nil, fmt.Errorf("found non-imports before imports: %w", ErrNoImports)
 	}
 
 	groups := importRe.FindStringSubmatch(string(src))
 	if groups[0] == "" {
-		return nil, ErrNoImports
+		return nil, fmt.Errorf("could not find imports: %w", ErrNoImports)
 	}
 
 	imports := strings.Split(groups[1], "\n")

format/struct.go

@@ -42,11 +42,11 @@ func (i importBlock) String() string {
 	var decl strings.Builder
 
 	decl.WriteString(strings.Join(importItemSlice(i.Stdlib), "\n\t"))
-	if len(i.Stdlib) > 0 {
+	if len(i.Module) > 0 {
 		decl.WriteString("\n\n\t")
 	}
 	decl.WriteString(strings.Join(importItemSlice(i.Module), "\n\t"))
-	if len(i.Module) > 0 {
+	if len(i.Other) > 0 {
 		decl.WriteString("\n\n\t")
 	}
 	decl.WriteString(strings.Join(importItemSlice(i.Other), "\n\t"))

imp.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"io/fs"
 	"os"
 	"path/filepath"
@@ -45,15 +46,18 @@ func runImp(root, ignore string, write bool) error {
 
 		data, err := os.ReadFile(walkPath)
 		if err != nil {
-			return err
+			return fmt.Errorf("could not read file %q: %w", walkPath, err)
 		}
 		formatted, err := format.Source(data, module)
 		if err != nil {
-			return err
+			return fmt.Errorf("could not format file %q: %w", walkPath, err)
 		}
 
 		if write {
-			return os.WriteFile(walkPath, formatted, walkInfo.Mode())
+			if err := os.WriteFile(walkPath, formatted, walkInfo.Mode()); err != nil {
+				return fmt.Errorf("could not write file %q: %w", walkPath, err)
+			}
+			return nil
 		}
 
 		if !bytes.Equal(data, formatted) {