From f33cc92b3736280a16d2a95f2611056aac681a90 Mon Sep 17 00:00:00 2001
From: David Jimenez <dvejmz@sgfault.com>
Date: Tue, 19 Oct 2021 23:02:24 +0100
Subject: [PATCH 1/2] feat: add debug logger

Provide logger implementation that allows writing application logs to a file if
`DEBUG` mode environment variable is enabled.

Signed-off-by: David Jimenez <dvejmz@sgfault.com>
---
 .gitignore        |  1 +
 logging/logger.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 main.go           |  8 ++++++++
 3 files changed, 51 insertions(+)
 create mode 100644 logging/logger.go

diff --git a/.gitignore b/.gitignore
index b11181c46..71f016325 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,4 @@ revive
 vendor
 *.swp
 dist/
+*.log
diff --git a/logging/logger.go b/logging/logger.go
new file mode 100644
index 000000000..f15d311f6
--- /dev/null
+++ b/logging/logger.go
@@ -0,0 +1,42 @@
+package logging
+
+import (
+	"io"
+	"io/ioutil"
+	"log"
+	"os"
+)
+
+var logger *log.Logger
+
+func GetLogger() (*log.Logger, error) {
+	if logger != nil {
+		return logger, nil
+	}
+
+	var writer io.Writer
+	var err error
+
+	debugModeEnabled := os.Getenv("DEBUG") == "1"
+	if debugModeEnabled {
+		writer, err = os.Create("revive.log")
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		// Suppress all logging output if debug mode is disabled
+		writer = ioutil.Discard
+	}
+
+	logger = log.New(writer, "", log.LstdFlags)
+
+	if !debugModeEnabled {
+		// Clear all flags to skip log output formatting step to increase
+		// performance somewhat if we're not logging anything
+		logger.SetFlags(0)
+	}
+
+	logger.Println("Logger initialised")
+
+	return logger, nil
+}
diff --git a/main.go b/main.go
index 12bd465f7..bb842bd13 100644
--- a/main.go
+++ b/main.go
@@ -13,6 +13,7 @@ import (
 	"github.com/mgechev/dots"
 	"github.com/mgechev/revive/config"
 	"github.com/mgechev/revive/lint"
+	"github.com/mgechev/revive/logging"
 	"github.com/mitchellh/go-homedir"
 )
 
@@ -29,6 +30,11 @@ func fail(err string) {
 }
 
 func main() {
+	log, err := logging.GetLogger()
+	if err != nil {
+		fail(err.Error())
+	}
+
 	conf, err := config.GetConfig(configPath)
 	if err != nil {
 		fail(err.Error())
@@ -60,6 +66,8 @@ func main() {
 		fail(err.Error())
 	}
 
+	log.Println("Config loaded")
+
 	failures, err := revive.Lint(packages, lintingRules, *conf)
 	if err != nil {
 		fail(err.Error())

From 732eb3ed26b1f1fa4fcd80866da7a7163b4b4bae Mon Sep 17 00:00:00 2001
From: David Jimenez <dvejmz@sgfault.com>
Date: Tue, 19 Oct 2021 23:22:21 +0100
Subject: [PATCH 2/2] style: add missing comment to exported function

Signed-off-by: David Jimenez <dvejmz@sgfault.com>
---
 logging/logger.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/logging/logger.go b/logging/logger.go
index f15d311f6..c911b2ec6 100644
--- a/logging/logger.go
+++ b/logging/logger.go
@@ -9,6 +9,8 @@ import (
 
 var logger *log.Logger
 
+// GetLogger retrieves an instance of an application logger which outputs
+// to a file if the debug flag is enabled
 func GetLogger() (*log.Logger, error) {
 	if logger != nil {
 		return logger, nil