text/template: Slice bound out of range error in text/template

[secsys-go]

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

$ go version
go version go1.17.8 linux/amd64

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="auto"
GOARCH="amd64"
GOBIN="/home/zjx/workspace/gowork/bin"
GOCACHE="/home/zjx/.cache/go-build"
GOENV="/home/zjx/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/zjx/workspace/gowork/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/zjx/workspace/gowork"
GOPRIVATE=""
GOPROXY="https://goproxy.cn,direct"
GOROOT="/home/zjx/.local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/zjx/.local/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.17.8"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/zjx/workspace/gowork/src/go-fdg-exmaples/std/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build1878510231=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I created an illegal text to parse as template.
A link on go.dev is : Poc.go

What did you expect to see?

It parses failed and return (nil, error)

What did you see instead?

It trigger a slice out of range fatal error, like:

panic: runtime error: slice bounds out of range [:12] with length 11

goroutine 6 [running]:
text/template/parse.(*lexer).emit(...)
	/usr/local/go-faketime/src/text/template/parse/lex.go:163
text/template/parse.lexRightDelim(0xc000108000)
	/usr/local/go-faketime/src/text/template/parse/lex.go:354 +0x29a
text/template/parse.(*lexer).run(0xc000108000)
	/usr/local/go-faketime/src/text/template/parse/lex.go:236 +0x2a
created by text/template/parse.lex
	/usr/local/go-faketime/src/text/template/parse/lex.go:229 +0x1ca

Program exited.

[seankhliao]

cc @robpike

[seankhliao]

I think #52527 is similar/dup?

[ianlancetaylor]

Yes, this is a dup. Don't use whitespace in delimiters.