diff --git a/altsrc/fg.py b/altsrc/fg.py
new file mode 100644
index 0000000000..f0d150f1be
--- /dev/null
+++ b/altsrc/fg.py
@@ -0,0 +1,45 @@
+# Only types that provide implementation of FlagInputSourceExtension can be listed here
+# please keep list sorted alphabetically
+flag_types = [
+    "Bool",
+    "Duration",
+    "Float64",
+    "Generic",
+    "Int",
+    "IntSlice",
+    "Path",
+    "String",
+    "StringSlice",
+]
+
+print('''// Code generated by fg.py; DO NOT EDIT.
+
+package altsrc
+
+import (
+	"flag"
+
+	"github.com/urfave/cli/v2"
+)''')
+
+for t in flag_types:
+    print(f'''
+// {t}Flag is the flag type that wraps cli.{t}Flag to allow
+// for other values to be specified
+type {t}Flag struct {{
+	*cli.{t}Flag
+	set *flag.FlagSet
+}}
+var _ FlagInputSourceExtension = (*{t}Flag)(nil)
+
+// New{t}Flag creates a new {t}Flag
+func New{t}Flag(fl *cli.{t}Flag) *{t}Flag {{
+	return &{t}Flag{{{t}Flag: fl, set: nil}}
+}}
+
+// Apply saves the flagSet for later usage calls, then calls
+// the wrapped {t}Flag.Apply
+func (f *{t}Flag) Apply(set *flag.FlagSet) error {{
+	f.set = set
+	return f.{t}Flag.Apply(set)
+}}''')
\ No newline at end of file
diff --git a/altsrc/flag_generated.go b/altsrc/flag_generated.go
index c9ecea82e9..bdaf5a5ff0 100644
--- a/altsrc/flag_generated.go
+++ b/altsrc/flag_generated.go
@@ -1,4 +1,4 @@
-// Code generated by fg; DO NOT EDIT.
+// Code generated by fg.py; DO NOT EDIT.
 
 package altsrc
 
@@ -14,6 +14,7 @@ type BoolFlag struct {
 	*cli.BoolFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*BoolFlag)(nil)
 
 // NewBoolFlag creates a new BoolFlag
 func NewBoolFlag(fl *cli.BoolFlag) *BoolFlag {
@@ -33,6 +34,7 @@ type DurationFlag struct {
 	*cli.DurationFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*DurationFlag)(nil)
 
 // NewDurationFlag creates a new DurationFlag
 func NewDurationFlag(fl *cli.DurationFlag) *DurationFlag {
@@ -52,6 +54,7 @@ type Float64Flag struct {
 	*cli.Float64Flag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*Float64Flag)(nil)
 
 // NewFloat64Flag creates a new Float64Flag
 func NewFloat64Flag(fl *cli.Float64Flag) *Float64Flag {
@@ -71,6 +74,7 @@ type GenericFlag struct {
 	*cli.GenericFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*GenericFlag)(nil)
 
 // NewGenericFlag creates a new GenericFlag
 func NewGenericFlag(fl *cli.GenericFlag) *GenericFlag {
@@ -84,31 +88,13 @@ func (f *GenericFlag) Apply(set *flag.FlagSet) error {
 	return f.GenericFlag.Apply(set)
 }
 
-// Int64Flag is the flag type that wraps cli.Int64Flag to allow
-// for other values to be specified
-type Int64Flag struct {
-	*cli.Int64Flag
-	set *flag.FlagSet
-}
-
-// NewInt64Flag creates a new Int64Flag
-func NewInt64Flag(fl *cli.Int64Flag) *Int64Flag {
-	return &Int64Flag{Int64Flag: fl, set: nil}
-}
-
-// Apply saves the flagSet for later usage calls, then calls
-// the wrapped Int64Flag.Apply
-func (f *Int64Flag) Apply(set *flag.FlagSet) error {
-	f.set = set
-	return f.Int64Flag.Apply(set)
-}
-
 // IntFlag is the flag type that wraps cli.IntFlag to allow
 // for other values to be specified
 type IntFlag struct {
 	*cli.IntFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*IntFlag)(nil)
 
 // NewIntFlag creates a new IntFlag
 func NewIntFlag(fl *cli.IntFlag) *IntFlag {
@@ -128,6 +114,7 @@ type IntSliceFlag struct {
 	*cli.IntSliceFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*IntSliceFlag)(nil)
 
 // NewIntSliceFlag creates a new IntSliceFlag
 func NewIntSliceFlag(fl *cli.IntSliceFlag) *IntSliceFlag {
@@ -141,42 +128,24 @@ func (f *IntSliceFlag) Apply(set *flag.FlagSet) error {
 	return f.IntSliceFlag.Apply(set)
 }
 
-// Int64SliceFlag is the flag type that wraps cli.Int64SliceFlag to allow
+// PathFlag is the flag type that wraps cli.PathFlag to allow
 // for other values to be specified
-type Int64SliceFlag struct {
-	*cli.Int64SliceFlag
+type PathFlag struct {
+	*cli.PathFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*PathFlag)(nil)
 
-// NewInt64SliceFlag creates a new Int64SliceFlag
-func NewInt64SliceFlag(fl *cli.Int64SliceFlag) *Int64SliceFlag {
-	return &Int64SliceFlag{Int64SliceFlag: fl, set: nil}
+// NewPathFlag creates a new PathFlag
+func NewPathFlag(fl *cli.PathFlag) *PathFlag {
+	return &PathFlag{PathFlag: fl, set: nil}
 }
 
 // Apply saves the flagSet for later usage calls, then calls
-// the wrapped Int64SliceFlag.Apply
-func (f *Int64SliceFlag) Apply(set *flag.FlagSet) error {
-	f.set = set
-	return f.Int64SliceFlag.Apply(set)
-}
-
-// Float64SliceFlag is the flag type that wraps cli.Float64SliceFlag to allow
-// for other values to be specified
-type Float64SliceFlag struct {
-	*cli.Float64SliceFlag
-	set *flag.FlagSet
-}
-
-// NewFloat64SliceFlag creates a new Float64SliceFlag
-func NewFloat64SliceFlag(fl *cli.Float64SliceFlag) *Float64SliceFlag {
-	return &Float64SliceFlag{Float64SliceFlag: fl, set: nil}
-}
-
-// Apply saves the flagSet for later usage calls, then calls the
-// wrapped Float64SliceFlag.Apply
-func (f *Float64SliceFlag) Apply(set *flag.FlagSet) error {
+// the wrapped PathFlag.Apply
+func (f *PathFlag) Apply(set *flag.FlagSet) error {
 	f.set = set
-	return f.Float64SliceFlag.Apply(set)
+	return f.PathFlag.Apply(set)
 }
 
 // StringFlag is the flag type that wraps cli.StringFlag to allow
@@ -185,6 +154,7 @@ type StringFlag struct {
 	*cli.StringFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*StringFlag)(nil)
 
 // NewStringFlag creates a new StringFlag
 func NewStringFlag(fl *cli.StringFlag) *StringFlag {
@@ -198,31 +168,13 @@ func (f *StringFlag) Apply(set *flag.FlagSet) error {
 	return f.StringFlag.Apply(set)
 }
 
-// PathFlag is the flag type that wraps cli.PathFlag to allow
-// for other values to be specified
-type PathFlag struct {
-	*cli.PathFlag
-	set *flag.FlagSet
-}
-
-// NewPathFlag creates a new PathFlag
-func NewPathFlag(fl *cli.PathFlag) *PathFlag {
-	return &PathFlag{PathFlag: fl, set: nil}
-}
-
-// Apply saves the flagSet for later usage calls, then calls the
-// wrapped PathFlag.Apply
-func (f *PathFlag) Apply(set *flag.FlagSet) error {
-	f.set = set
-	return f.PathFlag.Apply(set)
-}
-
 // StringSliceFlag is the flag type that wraps cli.StringSliceFlag to allow
 // for other values to be specified
 type StringSliceFlag struct {
 	*cli.StringSliceFlag
 	set *flag.FlagSet
 }
+var _ FlagInputSourceExtension = (*StringSliceFlag)(nil)
 
 // NewStringSliceFlag creates a new StringSliceFlag
 func NewStringSliceFlag(fl *cli.StringSliceFlag) *StringSliceFlag {
@@ -235,41 +187,3 @@ func (f *StringSliceFlag) Apply(set *flag.FlagSet) error {
 	f.set = set
 	return f.StringSliceFlag.Apply(set)
 }
-
-// Uint64Flag is the flag type that wraps cli.Uint64Flag to allow
-// for other values to be specified
-type Uint64Flag struct {
-	*cli.Uint64Flag
-	set *flag.FlagSet
-}
-
-// NewUint64Flag creates a new Uint64Flag
-func NewUint64Flag(fl *cli.Uint64Flag) *Uint64Flag {
-	return &Uint64Flag{Uint64Flag: fl, set: nil}
-}
-
-// Apply saves the flagSet for later usage calls, then calls
-// the wrapped Uint64Flag.Apply
-func (f *Uint64Flag) Apply(set *flag.FlagSet) error {
-	f.set = set
-	return f.Uint64Flag.Apply(set)
-}
-
-// UintFlag is the flag type that wraps cli.UintFlag to allow
-// for other values to be specified
-type UintFlag struct {
-	*cli.UintFlag
-	set *flag.FlagSet
-}
-
-// NewUintFlag creates a new UintFlag
-func NewUintFlag(fl *cli.UintFlag) *UintFlag {
-	return &UintFlag{UintFlag: fl, set: nil}
-}
-
-// Apply saves the flagSet for later usage calls, then calls
-// the wrapped UintFlag.Apply
-func (f *UintFlag) Apply(set *flag.FlagSet) error {
-	f.set = set
-	return f.UintFlag.Apply(set)
-}