context use: don't create/update config file and directories if not needed

[thaJeztah]

• relates to command: print appropriate warning messages on 'context list'/'contex… #3668

context use: skip validation for "default" context

This code was handling validation and parsing, only to discard the results if it was the default context.

context use: don't create/update config file and directories if not needed

Avoid updating the config-file if nothing changed. This also prevents creating
the file and config-directory if the default is used and no config-file existed
yet.

config.Save() performs various steps (creating the directory, updating
or copying permissions, etc etc), which are not needed if the defaults are
used;

cli/cli/config/configfile/file.go

Lines 135 to 176 in a445d97

	// Save encodes and writes out all the authorization information
	func (configFile *ConfigFile) Save() (retErr error) {
	if configFile.Filename == "" {
	return errors.Errorf("Can't save config with empty filename")
	}
	dir := filepath.Dir(configFile.Filename)
	if err := os.MkdirAll(dir, 0700); err != nil {
	return err
	}
	temp, err := os.CreateTemp(dir, filepath.Base(configFile.Filename))
	if err != nil {
	return err
	}
	defer func() {
	temp.Close()
	if retErr != nil {
	if err := os.Remove(temp.Name()); err != nil {
	logrus.WithError(err).WithField("file", temp.Name()).Debug("Error cleaning up temp file")
	}
	}
	}()
	err = configFile.SaveToWriter(temp)
	if err != nil {
	return err
	}
	if err := temp.Close(); err != nil {
	return errors.Wrap(err, "error closing temp file")
	}
	// Handle situation where the configfile is a symlink
	cfgFile := configFile.Filename
	if f, err := os.Readlink(cfgFile); err == nil {
	cfgFile = f
	}
	// Try copying the current config file (if any) ownership and permissions
	copyFilePermissions(cfgFile, temp.Name())
	return os.Rename(temp.Name(), cfgFile)
	}

- Description for the changelog

The client no longer creates or updates the CLI config file when running `docker context use` and the selected context is the current context.

- A picture of a cute animal (not mandatory but encouraged)

[codecov-commenter]

Codecov Report

Merging #3721 (7963778) into master (7963778) will not change coverage.
The diff coverage is n/a.

❗ Current head 7963778 differs from pull request most recent head f87d7ed. Consider uploading reports for the commit f87d7ed to get more accurate results

@@           Coverage Diff           @@
##           master    #3721   +/-   ##
=======================================
  Coverage   59.11%   59.11%           
=======================================
  Files         289      289           
  Lines       24665    24665           
=======================================
  Hits        14581    14581           
  Misses       9212     9212           
  Partials      872      872           

[thaJeztah]

@nicks @rumpl @vvoland PTAL

[vvoland]

Redundant last assert

[thaJeztah]

nice catch; sloppy copy/paste 😅

fixed!

[thaJeztah]

All green; let's get this one in