Add min length rule for library.properties url field

Previously, the permissive compliance mode only required that the library.properties url field was present. The field was
allowed to be empty in this mode.

Investigation revealed that the Arduino Library Manager indexer system, which Arduino Lint's permissive compliance mode
is intended to match, requires the url field value to be at least one character long:

https://github.com/arduino/libraries-repository-engine/blob/c395aaf14e7568f585a6a96350b584682a3c7feb/libraries/metadata/metadata.go#L110

Author: per1234

etc/schemas/arduino-library-properties-definitions-schema.json

@@ -413,6 +413,9 @@
             "allOf": [
               {
                 "type": "string"
+              },
+              {
+                "minLength": 1
               }
             ]
           }

internal/rule/ruleconfiguration/ruleconfiguration.go

@@ -889,6 +889,22 @@ var configurations = []Type{
 		ErrorModes:       []rulemode.Type{rulemode.Default},
 		RuleFunction:     rulefunction.LibraryPropertiesUrlFieldMissing,
 	},
+	{
+		ProjectType:      projecttype.Library,
+		SuperprojectType: projecttype.All,
+		Category:         "library.properties",
+		Subcategory:      "url field",
+		ID:               "LP056",
+		Brief:            "url < min length",
+		Description:      "",
+		MessageTemplate:  "library.properties url value is less than minimum length.",
+		DisableModes:     nil,
+		EnableModes:      []rulemode.Type{rulemode.Default},
+		InfoModes:        nil,
+		WarningModes:     nil,
+		ErrorModes:       []rulemode.Type{rulemode.Default},
+		RuleFunction:     rulefunction.LibraryPropertiesUrlFieldLTMinLength,
+	},
 	{
 		ProjectType:      projecttype.Library,
 		SuperprojectType: projecttype.All,

internal/rule/rulefunction/library.go

@@ -944,6 +944,23 @@ func LibraryPropertiesUrlFieldMissing() (result ruleresult.Type, output string)
 	return ruleresult.Pass, ""
 }
 
+// LibraryPropertiesUrlFieldLTMinLength checks if the library.properties "url" value is less than the minimum length.
+func LibraryPropertiesUrlFieldLTMinLength() (result ruleresult.Type, output string) {
+	if projectdata.LibraryPropertiesLoadError() != nil {
+		return ruleresult.NotRun, "Couldn't load library.properties"
+	}
+
+	if !projectdata.LibraryProperties().ContainsKey("url") {
+		return ruleresult.NotRun, "Field not present"
+	}
+
+	if schema.PropertyLessThanMinLength("url", projectdata.LibraryPropertiesSchemaValidationResult()[compliancelevel.Permissive]) {
+		return ruleresult.Fail, ""
+	}
+
+	return ruleresult.Pass, ""
+}
+
 // LibraryPropertiesUrlFieldInvalid checks whether the library.properties "url" value has a valid URL format.
 func LibraryPropertiesUrlFieldInvalid() (result ruleresult.Type, output string) {
 	if projectdata.LibraryPropertiesLoadError() != nil {

internal/rule/rulefunction/library_test.go

@@ -714,6 +714,17 @@ func TestLibraryPropertiesUrlFieldMissing(t *testing.T) {
 	checkLibraryRuleFunction(LibraryPropertiesUrlFieldMissing, testTables, t)
 }
 
+func TestLibraryPropertiesUrlFieldLTMinLength(t *testing.T) {
+	testTables := []libraryRuleFunctionTestTable{
+		{"Invalid", "InvalidLibraryProperties", ruleresult.NotRun, ""},
+		{"Legacy", "Legacy", ruleresult.NotRun, ""},
+		{"url field too short", "UrlLTMinLength", ruleresult.Fail, ""},
+		{"Valid", "Recursive", ruleresult.Pass, ""},
+	}
+
+	checkLibraryRuleFunction(LibraryPropertiesUrlFieldLTMinLength, testTables, t)
+}
+
 func TestLibraryPropertiesUrlFieldInvalid(t *testing.T) {
 	testTables := []libraryRuleFunctionTestTable{
 		{"Invalid", "InvalidLibraryProperties", ruleresult.NotRun, ""},

internal/rule/rulefunction/testdata/libraries/UrlLTMinLength/library.properties

@@ -0,0 +1,10 @@
+name=UrlLTMinLength
+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=
+architectures=avr
+includes=UrlLTMinLength.h

internal/rule/rulefunction/testdata/libraries/UrlLTMinLength/src/UrlLTMinLength.h

@@ -1832,6 +1832,9 @@ var _arduinoLibraryPropertiesDefinitionsSchemaJson = []byte(`{
             "allOf": [
               {
                 "type": "string"
+              },
+              {
+                "minLength": 1
               }
             ]
           }