x/text: Title() behaves differently than strings.Title()

[hangxie]

What version of Go are you using (go version)?

$ go version
go version go1.18 darwin/arm64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/Users/xiehang/Library/Caches/go-build"
GOENV="/Users/xiehang/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/xiehang/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/xiehang/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.18/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.18/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.18"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/xiehang/dev/parquet-tools/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 arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/vj/wtn1vqpj12g4k75p7snx28d80000gn/T/go-build3311008797=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

https://go.dev/play/p/qGo_iTp7AQ7

What did you expect to see?

cases.Title() behaves the same as strings.Title(), I believe this is what #48367 tells (explicitly)

What did you see instead?

cases.Title() changes the first character to uppercase, and change rest of the string lowercase
strings.Title() changes the first character to uppercase, leave rest of the string untouched.

[frederikhors]

Surprisingly, in the same minutes you, @hangxie and I discovered the same problems: #48367 (comment).

[ianlancetaylor]

I'm not sure there is anything to do here. Evidently we were mistaken in thinking that cases.Title was a drop-in replacement for strings.Title. Sorry about that. But changing cases.Title would lead to compatibility concerns. And the deprecation notice for strings.Title doesn't actually refer to cases.Title.

I'm open to suggestions.

[smasher164]

cases.Title does work as a substitute for strings.Title as long as you pass in the cases.NoLower option to the Caser.
The corrected version of the example should be
https://go.dev/play/p/uzYSvdtKNRy

package main

import (
	"fmt"
	"strings"

	"golang.org/x/text/cases"
	"golang.org/x/text/language"
)

func main() {
	orig := "thisIsCool"
	c := cases.Title(language.Und, cases.NoLower).String(orig)
	s := strings.Title(orig)
	fmt.Printf("orig: %s\ncases: %s\nstrings: %s\n", orig, c, s)
}

which outputs

orig: thisIsCool
cases: ThisIsCool
strings: ThisIsCool

[hangxie]

cases.Title does work as a substitute for strings.Title as long as you pass in the cases.NoLower option to the Caser.

Perfect, thank you!