Use a local Walk function (#421)

* Use a local Walk function

Because arduino-cli segfaults when sketchDir is a symbolic link, a simple
walk function is introduced with a twofold effect:
- fix the segfault
- allow to use symlinks

ref: https://www.google.com/search?q=golang+Walk+does+not+follow+symbolic+links

* tabs

* style

* comment

* retrigger CI

* retrigger CI

* style

* check sketch for being a file

* check sketch is not a directory

* additions:
- act on error in walk function (OS can detect symbolic links loops (lnk -> lnk))
- add a deepness detector for non trivial loops (dir/lnk -> ../..)

* fixes from "task check"

* updates per review

* style

* Update arduino/builder/sketch.go

Co-Authored-By: Roberto Sora <[email protected]>

* fixes

Author: d-a-v

Diff for: arduino/builder/sketch.go

@@ -25,10 +25,16 @@ import (
 
 	"github.com/arduino/arduino-cli/arduino/globals"
 	"github.com/arduino/arduino-cli/arduino/sketch"
+	"github.com/arduino/arduino-cli/cli/errorcodes"
+	"github.com/arduino/arduino-cli/cli/feedback"
 
 	"github.com/pkg/errors"
 )
 
+// As currently implemented on Linux,
+// the maximum number of symbolic links that will be followed while resolving a pathname is 40
+const maxFileSystemDepth = 40
+
 var includesArduinoH = regexp.MustCompile(`(?m)^\s*#\s*include\s*[<\"]Arduino\.h[>\"]`)
 
 // QuoteCppString returns the given string as a quoted string for use with the C
@@ -58,6 +64,39 @@ func SketchSaveItemCpp(item *sketch.Item, destPath string) error {
 	return nil
 }
 
+// simpleLocalWalk locally replaces filepath.Walk and/but goes through symlinks
+func simpleLocalWalk(root string, maxDepth int, walkFn func(path string, info os.FileInfo, err error) error) error {
+
+	info, err := os.Stat(root)
+
+	if err != nil {
+		return walkFn(root, nil, err)
+	}
+
+	err = walkFn(root, info, err)
+	if err == filepath.SkipDir {
+		return nil
+	}
+
+	if info.IsDir() {
+		if maxDepth <= 0 {
+			return walkFn(root, info, errors.New("Filesystem bottom is too deep (directory recursion or filesystem really deep): "+root))
+		}
+		maxDepth--
+		files, err := ioutil.ReadDir(root)
+		if err == nil {
+			for _, file := range files {
+				err = simpleLocalWalk(root+string(os.PathSeparator)+file.Name(), maxDepth, walkFn)
+				if err == filepath.SkipDir {
+					return nil
+				}
+			}
+		}
+	}
+
+	return nil
+}
+
 // SketchLoad collects all the files composing a sketch.
 // The parameter `sketchPath` holds a path pointing to a single sketch file or a sketch folder,
 // the path must be absolute.
@@ -79,14 +118,28 @@ func SketchLoad(sketchPath, buildPath string) (*sketch.Sketch, error) {
 			return nil, errors.Wrap(err, "unable to find the main sketch file")
 		}
 		f.Close()
+		// ensure it is not a directory
+		info, err := os.Stat(mainSketchFile)
+		if err != nil {
+			return nil, errors.Wrap(err, "unable to check the main sketch file")
+		}
+		if info.IsDir() {
+			return nil, errors.Wrap(errors.New(mainSketchFile), "sketch must not be a directory")
+		}
 	} else {
 		sketchFolder = filepath.Dir(sketchPath)
 		mainSketchFile = sketchPath
 	}
 
 	// collect all the sketch files
 	var files []string
-	err = filepath.Walk(sketchFolder, func(path string, info os.FileInfo, err error) error {
+	err = simpleLocalWalk(sketchFolder, maxFileSystemDepth, func(path string, info os.FileInfo, err error) error {
+
+		if err != nil {
+			feedback.Errorf("Error during sketch processing: %v", err)
+			os.Exit(errorcodes.ErrGeneric)
+		}
+
 		// ignore hidden files and skip hidden directories
 		if strings.HasPrefix(info.Name(), ".") {
 			if info.IsDir() {