Shell completions are broken when login shell is different than currently active shell

My urfave/cli version is

2.27.1

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
Did you perform a search about this problem? Here's the GitHub guide about searching.

Dependency Management

My project is using go modules.

Describe the bug

Shell completions to show are determined by looking at contents of the $SHELL environment variable, which isn't a reliable way to do this because the current login shell isn't always the current active shell.

cli/help.go

Lines 153 to 161 in 7656c5f

    
           if strings.HasSuffix(os.Getenv("SHELL"), "zsh") { 
        
           	for _, name := range command.Names() { 
        
           		_, _ = fmt.Fprintf(writer, "%s:%s\n", name, command.Usage) 
        
           	} 
        
           } else { 
        
           	for _, name := range command.Names() { 
        
           		_, _ = fmt.Fprintf(writer, "%s\n", name) 
        
           	} 
        
           }

To reproduce

Here's my simple CLI app with shell completions.

Observed behavior

My shell is Zsh, and when I run:

$ fhome [tab]
config     -- Manage system configuration
event      -- Manage events
help    h  -- Shows a list of commands or help for one command
object  o  -- Manage objects

but when I run Bash first and then trigger completions, my CLI tools still outputs Zsh-style completions:

$ bash
bash-5.2$ fhome
a              commands       configuration  events         h:Shows        help:Shows     o:Manage       objects        one            system
command        config:Manage  event:Manage   for            help           list           object:Manage  of             or

Expected behavior

I expect shell completion to work for the current active shell, so this bug won't happen.

Additional context

Maybe we can take a look at how Cobra does it.
This also occurs in v3 alpha, please add appropriate labels

Want to fix this yourself?

Sure!

Run `go version` and paste its output here

$ go version
go version go1.22.2 darwin/arm64

Run `go env` and paste its output here

$ go env
GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/bartek/Library/Caches/go-build'
GOENV='/Users/bartek/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/bartek/.cache/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/bartek/.cache/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/opt/homebrew/Cellar/go/1.22.2/libexec'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/Cellar/go/1.22.2/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.2'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/bartek/projects/fhome/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/r6/5z0bypqn4cb8p369zlrfhw3c0000gn/T/go-build3283617553=/tmp/go-build -gno-record-gcc-switches -fno-common'

	if strings.HasSuffix(os.Getenv("SHELL"), "zsh") {
	for _, name := range command.Names() {
	_, _ = fmt.Fprintf(writer, "%s:%s\n", name, command.Usage)
	}
	} else {
	for _, name := range command.Names() {
	_, _ = fmt.Fprintf(writer, "%s\n", name)
	}
	}