save+util: Provide a meaningful error message for safe (over-)write fails

cmd/micro/clean.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bufio"
 	"encoding/gob"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -11,6 +12,7 @@ import (
 
 	"github.com/zyedidia/micro/v2/internal/buffer"
 	"github.com/zyedidia/micro/v2/internal/config"
+	"github.com/zyedidia/micro/v2/internal/util"
 )
 
 func shouldContinue() bool {
@@ -42,7 +44,11 @@ func CleanConfig() {
 	settingsFile := filepath.Join(config.ConfigDir, "settings.json")
 	err := config.WriteSettings(settingsFile)
 	if err != nil {
-		fmt.Println("Error writing settings.json file: " + err.Error())
+		if errors.Is(err, util.ErrOverwrite) {
+			fmt.Println(err.Error())
+		} else {
+			fmt.Println("Error writing settings.json file: " + err.Error())
+		}
 	}
 
 	// detect unused options
@@ -80,7 +86,11 @@ func CleanConfig() {
 
 			err := config.OverwriteSettings(settingsFile)
 			if err != nil {
-				fmt.Println("Error overwriting settings.json file: " + err.Error())
+				if errors.Is(err, util.ErrOverwrite) {
+					fmt.Println(err.Error())
+				} else {
+					fmt.Println("Error overwriting settings.json file: " + err.Error())
+				}
 			}
 
 			fmt.Println("Removed unused options")

internal/action/command.go

@@ -658,7 +658,16 @@ func SetGlobalOptionNative(option string, nativeValue interface{}) error {
 		delete(b.LocalSettings, option)
 	}
 
-	return config.WriteSettings(filepath.Join(config.ConfigDir, "settings.json"))
+	err := config.WriteSettings(filepath.Join(config.ConfigDir, "settings.json"))
+	if err != nil {
+		if errors.Is(err, util.ErrOverwrite) {
+			screen.TermMessage(err)
+			err = errors.Unwrap(err)
+		}
+		return err
+	}
+
+	return nil
 }
 
 func SetGlobalOption(option, value string) error {
@@ -783,7 +792,11 @@ func (h *BufPane) BindCmd(args []string) {
 
 	_, err := TryBindKey(parseKeyArg(args[0]), args[1], true)
 	if err != nil {
-		InfoBar.Error(err)
+		if errors.Is(err, util.ErrOverwrite) {
+			screen.TermMessage(err)
+		} else {
+			InfoBar.Error(err)
+		}
 	}
 }
 
@@ -796,7 +809,11 @@ func (h *BufPane) UnbindCmd(args []string) {
 
 	err := UnbindKey(parseKeyArg(args[0]))
 	if err != nil {
-		InfoBar.Error(err)
+		if errors.Is(err, util.ErrOverwrite) {
+			screen.TermMessage(err)
+		} else {
+			InfoBar.Error(err)
+		}
 	}
 }
 

internal/buffer/save.go

@@ -316,6 +316,10 @@ func (b *Buffer) saveToFile(filename string, withSudo bool, autoSave bool) error
 	result := <-saveResponseChan
 	err = result.err
 	if err != nil {
+		if errors.Is(err, util.ErrOverwrite) {
+			screen.TermMessage(err)
+			err = errors.Unwrap(err)
+		}
 		return err
 	}
 
@@ -371,6 +375,7 @@ func (b *Buffer) safeWrite(path string, withSudo bool, newFile bool) (int, error
 	b.forceKeepBackup = true
 	size, err := file.Write(b)
 	if err != nil {
+		err = util.OverwriteError{err, backupName}
 		return size, err
 	}
 	b.forceKeepBackup = false

internal/util/util.go

@@ -45,11 +45,44 @@ var (
 	Stdout *bytes.Buffer
 	// Sigterm is a channel where micro exits when written
 	Sigterm chan os.Signal
+
+	// To be used for fails on (over-)write with safe writes
+	ErrOverwrite = OverwriteError{}
 )
 
 // To be used for file writes before umask is applied
 const FileMode os.FileMode = 0666
 
+const OverwriteFailMsg = `An error occurred while writing to the file:
+
+%s
+
+The file may be corrupted now. The good news is that it has been
+successfully backed up. Next time you open this file with Micro,
+Micro will ask if you want to recover it from the backup.
+
+The backup path is:
+
+%s`
+
+// OverwriteError is a custom error to add additional information
+type OverwriteError struct {
+	What       error
+	BackupName string
+}
+
+func (e OverwriteError) Error() string {
+	return fmt.Sprintf(OverwriteFailMsg, e.What, e.BackupName)
+}
+
+func (e OverwriteError) Is(target error) bool {
+	return target == ErrOverwrite
+}
+
+func (e OverwriteError) Unwrap() error {
+	return e.What
+}
+
 func init() {
 	var err error
 	SemVersion, err = semver.Make(Version)
@@ -685,6 +718,8 @@ func SafeWrite(path string, bytes []byte, rename bool) error {
 	if err != nil {
 		if rename {
 			os.Remove(tmp)
+		} else {
+			err = OverwriteError{err, tmp}
 		}
 		return err
 	}