urfave / cli

My urfave/cli version is

github.com/urfave/cli/v2 v2.25.3

Checklist

Are you running the latest v2 release? The list of releases is here.
Did you check the manual for your release? The v2 manual is here
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Dependency Management

My project is using go modules.

Describe the bug

When defining a TimestampFlag with an alias, calling ctx.IsSet on the name (not the alias) returns false when the alias is used in the command line.

To reproduce

https://go.dev/play/p/WMR_blIb2kf

package main

import (
	"fmt"
	"log"

	"github.com/urfave/cli/v2"
)

func main() {
	app := &cli.App{
		Flags: []cli.Flag{
			&cli.TimestampFlag{
				Name:    "meeting",
				Aliases: []string{"m"},
				Layout:  "2006-01-02T15:04:05",
			},
		},
		Action: func(cCtx *cli.Context) error {
			fmt.Printf("meeting is set = %v\n", cCtx.IsSet("meeting"))
			fmt.Printf("meeting = %s\n", cCtx.Timestamp("meeting").String())
			return nil
		},
	}

	if err := app.Run([]string{"exe", "--meeting", "2019-08-12T15:04:05"}); err != nil {
		log.Fatal(err)
	}
	if err := app.Run([]string{"exe", "-m", "2019-08-12T15:04:05"}); err != nil {
		log.Fatal(err)
	}
}

meeting is set = true
meeting = 2019-08-12 15:04:05 +0000 UTC
meeting is set = false <-- should be true
meeting = 2019-08-12 15:04:05 +0000 UTC

Observed behavior

cCtx.IsSet("meeting") returns false for the call with -m=...

Expected behavior

cCtx.IsSet("meeting") should return true if using the alias -m=...

Additional context

cli/flag.go

Line 199 in acbbbf2

_ = set.Set(name, ff.Value.String())

Issue seems to be here, in copyFlag, when converting the value of the flag to String, can't be decoded by golang flag package

Run `go version` and paste its output here

go version go1.19.8 darwin/amd64

Run `go env` and paste its output here

GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/tchandelle/Library/Caches/go-build"
GOENV="/Users/tchandelle/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/tchandelle/.asdf/installs/golang/1.19.8/packages/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/tchandelle/.asdf/installs/golang/1.19.8/packages"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/tchandelle/.asdf/installs/golang/1.19.8/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/tchandelle/.asdf/installs/golang/1.19.8/go/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.19.8"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/tchandelle/git/nodeum/nodeum-v2/data_management/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/wc/1rp4395x1_bf48vw43ftrm1r0000gn/T/go-build97822141=/tmp/go-build -gno-record-gcc-switches -fno-common"

@tchandelle Yes this is definitely a bug. Would you like to submit a PR to fix this ?

IsSet for aliases of TimestampFlag doesn't work