Add check for misspelled library extras folder name

Author: per1234

Diff for: check/checkconfigurations/checkconfigurations.go

@@ -911,6 +911,21 @@ var configurations = []Type{
 		ErrorModes:      []checkmode.Type{checkmode.Default},
 		CheckFunction:   checkfunctions.LibraryFolderNameGTMaxLength,
 	},
+	{
+		ProjectType:     projecttype.Library,
+		Category:        "structure",
+		Subcategory:     "",
+		ID:              "",
+		Brief:           "incorrect extras folder name",
+		Description:     "",
+		MessageTemplate: "Potentially misspelled extras folder name found: {{.}}. See: https://arduino.github.io/arduino-cli/latest/library-specification/#extra-documentation",
+		DisableModes:    nil,
+		EnableModes:     []checkmode.Type{checkmode.All},
+		InfoModes:       nil,
+		WarningModes:    []checkmode.Type{checkmode.All},
+		ErrorModes:      nil,
+		CheckFunction:   checkfunctions.MisspelledExtrasFolderName,
+	},
 	{
 		ProjectType:     projecttype.Sketch,
 		Category:        "structure",

Diff for: check/checkfunctions/checkfunctions.go

@@ -20,6 +20,7 @@ import (
 	"regexp"
 
 	"github.com/arduino/arduino-check/check/checkresult"
+	"github.com/arduino/go-paths-helper"
 )
 
 // Type is the function signature for the check functions.
@@ -31,3 +32,18 @@ func validProjectPathBaseName(name string) bool {
 	baseNameRegexp := regexp.MustCompile("^[a-zA-Z0-9][a-zA-Z0-9_.-]*$")
 	return baseNameRegexp.MatchString(name)
 }
+
+func containsMisspelledPathBaseName(pathList paths.PathList, correctBaseName string, misspellingQuery string) (*paths.Path, bool) {
+	misspellingRegexp := regexp.MustCompile(misspellingQuery)
+	for _, path := range pathList {
+		if path.Base() == correctBaseName {
+			return nil, false
+		}
+
+		if misspellingRegexp.MatchString(path.Base()) {
+			return path, true
+		}
+	}
+
+	return nil, false
+}

Diff for: check/checkfunctions/library.go

@@ -965,6 +965,22 @@ func LibraryFolderNameGTMaxLength() (result checkresult.Type, output string) {
 	return checkresult.Pass, ""
 }
 
+// MisspelledExtrasFolderName checks for incorrectly spelled `extras` folder name.
+func MisspelledExtrasFolderName() (result checkresult.Type, output string) {
+	directoryListing, err := checkdata.ProjectPath().ReadDir()
+	if err != nil {
+		panic(err)
+	}
+	directoryListing.FilterDirs()
+
+	path, found := containsMisspelledPathBaseName(directoryListing, "extras", "(?i)^extra$")
+	if found {
+		return checkresult.Fail, path.String()
+	}
+
+	return checkresult.Pass, ""
+}
+
 // spellCheckLibraryPropertiesFieldValue returns the value of the provided library.properties field with commonly misspelled words corrected.
 func spellCheckLibraryPropertiesFieldValue(fieldName string) (result checkresult.Type, output string) {
 	if checkdata.LibraryPropertiesLoadError() != nil {

Diff for: check/checkfunctions/library_test.go

@@ -272,3 +272,13 @@ func TestLibraryFolderNameGTMaxLength(t *testing.T) {
 
 	checkLibraryCheckFunction(LibraryFolderNameGTMaxLength, testTables, t)
 }
+
+func TestMisspelledExtrasFolderName(t *testing.T) {
+	testTables := []libraryCheckFunctionTestTable{
+		{"Correctly spelled", "ExtrasFolder", checkresult.Pass, ""},
+		{"Misspelled", "MisspelledExtrasFolder", checkresult.Fail, ""},
+		{"No extras folder", "Recursive", checkresult.Pass, ""},
+	}
+
+	checkLibraryCheckFunction(MisspelledExtrasFolderName, testTables, t)
+}

Diff for: check/checkfunctions/testdata/libraries/ExtrasFolder/extras/.gitkeep

@@ -0,0 +1,9 @@
+name=ExtrasFolder
+version=1.0.0
+author=Cristian Maglie <[email protected]>, Pippo Pluto <[email protected]>
+maintainer=Cristian Maglie <[email protected]>
+sentence=A library that makes coding a web server a breeze.
+paragraph=Supports HTTP1.1 and you can do GET and POST.
+category=Communication
+url=http://example.com/
+architectures=avr

Diff for: check/checkfunctions/testdata/libraries/ExtrasFolder/library.properties

@@ -0,0 +1,9 @@
+name=MisspelledExtrasFolder
+version=1.0.0
+author=Cristian Maglie <[email protected]>, Pippo Pluto <[email protected]>
+maintainer=Cristian Maglie <[email protected]>
+sentence=A library that makes coding a web server a breeze.
+paragraph=Supports HTTP1.1 and you can do GET and POST.
+category=Communication
+url=http://example.com/
+architectures=avr