Create rule S6423: Always log failures in Azure Functions (#960)

rules/S6423/csharp/metadata.json

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+{
+  "title": "Azure Functions should log all failures.",
+  "type": "CODE_SMELL",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "5min"
+  },
+  "tags": [
+    "error-handling"
+  ],
+  "defaultSeverity": "Major",
+  "ruleSpecification": "RSPEC-6423",
+  "sqKey": "S6423",
+  "scope": "Main",
+  "defaultQualityProfiles": [ ],
+  "quickfix": "unknown"
+}

rules/S6423/csharp/rule.adoc

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+Capturing and logging errors is critical to monitoring the health of your Azure Functions application.
+
+Each `catch` block inside an Azure Function should log helpful details about the failure. Moreover, the logging should not be done at `Debug` or `Trace` level.
+
+Consider using the built-in integration with Application Insights for better monitoring of your Application.
+
+// If you want to factorize the description uncomment the following line and create the file.
+//include::../description.adoc[]
+
+== Noncompliant Code Example
+
+[source,csharp]
+----
+[FunctionName("Foo")]
+public static async Task<IActionResult> Run(
+	[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
+	ILogger log)
+{
+	try
+	{
+		// do stuff that can fail
+	}
+	catch (Exception ex)
+	{
+		// the failure is not logged at all OR is logged at DEBUG/TRACE level
+	}
+}
+----
+
+== Compliant Solution
+
+[source,csharp]
+----
+[FunctionName("Foo")]
+public static async Task<IActionResult> Run(
+	[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req,
+	ILogger log)
+{
+	try
+	{
+		// do stuff that can fail
+	}
+	catch (Exception ex)
+	{
+		log.LogError("Give details that will help investigations", ex);
+	}
+}
+----
+
+== See
+
+* https://docs.microsoft.com/en-us/azure/azure-functions/functions-bindings-error-pages?tabs=csharp[Azure Functions error handling and retries]
+* https://docs.microsoft.com/en-us/azure/azure-functions/functions-monitoring[Monitor Azure Functions]
+* https://docs.microsoft.com/en-us/azure/azure-monitor/app/azure-functions-supported-features[Application Insights for Azure Functions supported features]

rules/S6423/metadata.json

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+{
+}