Add check for sketch.json invalid JSON document

Author: per1234

Diff for: .prettierignore

@@ -8,3 +8,4 @@
 /check/checkdata/schema/testdata/invalid-schema.json
 /check/checkdata/testdata/packageindexes/invalid-JSON/package_foo_index.json
 /check/checkfunctions/testdata/packageindexes/invalid-JSON/package_foo_index.json
+/check/checkfunctions/testdata/sketches/InvalidJSONMetadataFile/sketch.json

Diff for: check/checkconfigurations/checkconfigurations.go

@@ -1211,6 +1211,21 @@ var configurations = []Type{
 		ErrorModes:      []checkmode.Type{checkmode.Strict},
 		CheckFunction:   checkfunctions.MissingLicenseFile,
 	},
+	{
+		ProjectType:     projecttype.Sketch,
+		Category:        "metadata",
+		Subcategory:     "sketch.json",
+		ID:              "",
+		Brief:           "invalid sketch.json JSON format",
+		Description:     "",
+		MessageTemplate: "sketch.json is not a valid JSON document. See: https://arduino.github.io/arduino-cli/latest/sketch-specification/#metadata",
+		DisableModes:    nil,
+		EnableModes:     []checkmode.Type{checkmode.Default},
+		InfoModes:       nil,
+		WarningModes:    []checkmode.Type{checkmode.Permissive},
+		ErrorModes:      []checkmode.Type{checkmode.Default},
+		CheckFunction:   checkfunctions.SketchDotJSONJSONFormat,
+	},
 	{
 		ProjectType:     projecttype.Sketch,
 		Category:        "code",

Diff for: check/checkfunctions/sketch.go

@@ -100,3 +100,17 @@ func PdeSketchExtension() (result checkresult.Type, output string) {
 
 	return checkresult.Pass, ""
 }
+
+// SketchDotJSONJSONFormat checks whether the sketch.json metadata file is a valid JSON document.
+func SketchDotJSONJSONFormat() (result checkresult.Type, output string) {
+	metadataPath := sketch.MetadataPath(checkdata.ProjectPath())
+	if metadataPath == nil {
+		return checkresult.NotRun, "No metadata file"
+	}
+
+	if isValidJSON(metadataPath) {
+		return checkresult.Pass, ""
+	}
+
+	return checkresult.Fail, ""
+}

Diff for: check/checkfunctions/sketch_test.go

@@ -95,3 +95,13 @@ func TestPdeSketchExtension(t *testing.T) {
 
 	checkSketchCheckFunction(PdeSketchExtension, testTables, t)
 }
+
+func TestSketchDotJSONJSONFormat(t *testing.T) {
+	testTables := []sketchCheckFunctionTestTable{
+		{"No metadata file", "NoMetadataFile", checkresult.NotRun, ""},
+		{"Valid", "ValidMetadataFile", checkresult.Pass, ""},
+		{"Invalid", "InvalidJSONMetadataFile", checkresult.Fail, ""},
+	}
+
+	checkSketchCheckFunction(SketchDotJSONJSONFormat, testTables, t)
+}

Diff for: check/checkfunctions/testdata/sketches/InvalidJSONMetadataFile/InvalidJSONMetadataFile.ino

@@ -0,0 +1,2 @@
+void setup() {}
+void loop() {}

Diff for: check/checkfunctions/testdata/sketches/InvalidJSONMetadataFile/sketch.json

@@ -0,0 +1,7 @@
+[
+  {
+    "foo": "bar"
+  },
+  {
+    "baz": "bat"
+  }

Diff for: check/checkfunctions/testdata/sketches/NoMetadataFile/NoMetadataFile.ino

@@ -0,0 +1,2 @@
+void setup() {}
+void loop() {}

Diff for: check/checkfunctions/testdata/sketches/ValidMetadataFile/ValidMetadataFile.ino

@@ -0,0 +1,2 @@
+void setup() {}
+void loop() {}

Diff for: check/checkfunctions/testdata/sketches/ValidMetadataFile/sketch.json

@@ -0,0 +1,6 @@
+{
+  "cpu": {
+    "fqbn": "arduino:avr:uno",
+    "port": ""
+  }
+}