Chore: Add altsrc flag definition generation

cmd/urfave-cli-genflags/Makefile

@@ -25,4 +25,5 @@ show-cover:
 
 .PHONY: run
 run: build
-	./urfave-cli-genflags
+	./urfave-cli-genflags	
+	./urfave-cli-genflags -f altsrc/flag-spec.yaml -o altsrc/flag_generated.go -p altsrc -a

cmd/urfave-cli-genflags/generated_altsrc.gotmpl

@@ -0,0 +1,34 @@
+// WARNING: this file is generated. DO NOT EDIT
+
+package {{.PackageName}}
+
+import (
+	"flag"
+	"github.com/urfave/cli/v2"
+)
+
+{{range .SortedFlagTypes}}
+// {{.TypeName}} is the flag type that wraps cli.{{.TypeName}} to allow
+// for other values to be specified
+type {{.TypeName}} struct {
+	*cli.{{.TypeName}}
+	set *flag.FlagSet
+}
+
+// New{{.TypeName}} creates a new {{.TypeName}}
+func New{{.TypeName}}(fl *cli.{{.TypeName}}) *{{.TypeName}} {
+	return &{{.TypeName}}{{"{"}}{{.TypeName}}: fl, set: nil}
+}
+
+// Apply saves the flagSet for later usage calls, then calls
+// the wrapped {{.TypeName}}.Apply
+func (f *{{.TypeName}}) Apply(set *flag.FlagSet) error {
+	f.set = set
+	return f.{{.TypeName}}.Apply(set)
+}
+{{end}}{{/* /range .SortedFlagTypes */}}
+
+// vim{{/* 👻 */}}:ro
+{{/*
+vim:filetype=gotexttmpl
+*/}}

cmd/urfave-cli-genflags/main.go

@@ -32,6 +32,9 @@ var (
 	//go:embed generated_test.gotmpl
 	TestTemplateString string
 
+	//go:embed generated_altsrc.gotmpl
+	AltsrcTemplateString string
+
 	titler = cases.Title(language.Und, cases.NoLower)
 )
 
@@ -58,6 +61,10 @@ func main() {
 		Name:  "genflags",
 		Usage: "Generate flag types for urfave/cli",
 		Flags: []cli.Flag{
+			&cli.BoolFlag{
+				Name:    "altsrc",
+				Aliases: []string{"a"},
+			},
 			&cli.PathFlag{
 				Name:    "flag-spec-yaml",
 				Aliases: []string{"f"},
@@ -148,12 +155,11 @@ func runGenFlags(cCtx *cli.Context) error {
 		spec.UrfaveCLITestNamespace = "cli."
 	}
 
-	genTmpl, err := template.New("gen").Parse(TemplateString)
-	if err != nil {
-		return err
+	templateString := TemplateString
+	if cCtx.IsSet("altsrc") {
+		templateString = AltsrcTemplateString
 	}
-
-	genTestTmpl, err := template.New("gen_test").Parse(TestTemplateString)
+	genTmpl, err := template.New("gen").Parse(templateString)
 	if err != nil {
 		return err
 	}
@@ -163,27 +169,33 @@ func runGenFlags(cCtx *cli.Context) error {
 		return err
 	}
 
-	genTestBuf := &bytes.Buffer{}
-	if err := genTestTmpl.Execute(genTestBuf, spec); err != nil {
-		return err
-	}
-
 	if err := os.WriteFile(cCtx.Path("generated-output"), genBuf.Bytes(), 0644); err != nil {
 		return err
 	}
 
-	if err := os.WriteFile(cCtx.Path("generated-test-output"), genTestBuf.Bytes(), 0644); err != nil {
-		return err
-	}
-
 	if _, err := sh(cCtx.Context, cCtx.Path("goimports"), "-w", cCtx.Path("generated-output")); err != nil {
 		return err
 	}
 
-	if _, err := sh(cCtx.Context, cCtx.Path("goimports"), "-w", cCtx.Path("generated-test-output")); err != nil {
-		return err
-	}
+	if !cCtx.IsSet("altsrc") {
+		genTestTmpl, err := template.New("gen_test").Parse(TestTemplateString)
+		if err != nil {
+			return err
+		}
 
+		genTestBuf := &bytes.Buffer{}
+		if err := genTestTmpl.Execute(genTestBuf, spec); err != nil {
+			return err
+		}
+
+		if err := os.WriteFile(cCtx.Path("generated-test-output"), genTestBuf.Bytes(), 0644); err != nil {
+			return err
+		}
+
+		if _, err := sh(cCtx.Context, cCtx.Path("goimports"), "-w", cCtx.Path("generated-test-output")); err != nil {
+			return err
+		}
+	}
 	return nil
 }