build: generate drivers with std lib only [skip ci]

Makefile

@@ -55,7 +55,6 @@ build: promu
 
 drivers-%:
 	@echo ">> generating drivers.go with selected drivers"
-	@$(GO) get github.com/dave/jennifer/jen
 	@$(GO) run drivers_gen.go -- $*
 	@$(GO) get ./...
 	@$(GO) mod tidy

drivers_gen.go

@@ -3,15 +3,16 @@
 package main
 
 import (
+	"bytes"
 	"fmt"
+	"go/format"
 	"os"
-
-	. "github.com/dave/jennifer/jen"
+	"sort"
 )
 
 const (
-	packageName string = "sql_exporter"
-	filename    string = "drivers.go"
+	packageName = "sql_exporter"
+	filename    = "drivers.go"
 )
 
 var driverList = map[string][]string{
@@ -33,37 +34,90 @@ var driverList = map[string][]string{
 }
 
 func main() {
-	var enabledDrivers []string
-
-	args := os.Args[2:]
+	// Accept either os.Args[2:] (keeps compatibility with previous usage)
+	// or os.Args[1:] (simple "go run drivers_gen.go minimal")
+	var args []string
+	if len(os.Args) >= 3 {
+		args = os.Args[2:]
+	} else {
+		args = os.Args[1:]
+	}
 
-	if args[0] == "all" {
+	if len(args) == 0 {
+		fmt.Printf("Usage: go run drivers_gen.go <key>\nAvailable keys:\n")
+		// Print keys in deterministic order
+		keys := make([]string, 0, len(driverList))
 		for k := range driverList {
-			if k != "custom" {
-				enabledDrivers = append(enabledDrivers, driverList[k]...)
+			keys = append(keys, k)
+		}
+		fmt.Printf(" - all\n")
+		for _, k := range keys {
+			fmt.Printf(" - %s\n", k)
+		}
+		os.Exit(1)
+	}
+
+	key := args[0]
+	var enabledDrivers []string
+
+	if key == "all" {
+		for k, list := range driverList {
+			if k == "custom" {
+				continue
 			}
+			enabledDrivers = append(enabledDrivers, list...)
 		}
 	} else {
-		var ok bool
-		enabledDrivers, ok = driverList[args[0]]
+		list, ok := driverList[key]
 		if !ok {
-			fmt.Printf("Nonexistent key. Do nothing.\n")
+			fmt.Printf("Nonexistent key '%s'. Do nothing.\n", key)
 			os.Exit(0)
 		}
+		enabledDrivers = append(enabledDrivers, list...)
 	}
 
-	f := NewFile(packageName)
-	f.HeaderComment("// Code generated by \"drivers_gen.go\"")
-	f.Anon(enabledDrivers...)
-	fmt.Println("Following drivers are to be added:")
+	if len(enabledDrivers) == 0 {
+		fmt.Println("No drivers selected; nothing to do.")
+		os.Exit(0)
+	}
 
-	for _, v := range enabledDrivers {
-		fmt.Printf("> %s\n", v)
+	// Create file contents
+	var b bytes.Buffer
+	fmt.Fprintf(&b, "// Code generated by \"drivers_gen.go\"\n\n")
+	fmt.Fprintf(&b, "package %s\n\n", packageName)
+	fmt.Fprintf(&b, "import (\n")
+	// Keep order stable and de-duplicate just in case
+	seen := map[string]bool{}
+	for _, d := range enabledDrivers {
+		seen[d] = true
 	}
+	unique := make([]string, 0, len(seen))
+	for d := range seen {
+		unique = append(unique, d)
+	}
+	sort.Strings(unique)
+	for _, d := range unique {
+		fmt.Fprintf(&b, "\t_ %q\n", d)
+	}
+	fmt.Fprintf(&b, ")\n")
 
+	// Format using gofmt
+	src, err := format.Source(b.Bytes())
+	if err != nil {
+		// If formatting fails, write the unformatted source and print a warning
+		fmt.Println("warning: go/format failed:", err)
+		src = b.Bytes()
+	}
+
+	// Print what will be written
+	fmt.Println("Following drivers are to be added:")
+	for _, v := range unique {
+		fmt.Printf("> %s\n", v)
+	}
 	fmt.Printf("Save to '%s'\n", filename)
-	if err := f.Save(filename); err != nil {
-		fmt.Println(err.Error())
+
+	if err := os.WriteFile(filename, src, 0644); err != nil {
+		fmt.Println("error writing file:", err)
 		os.Exit(1)
 	}
 }