Why does go build succeed for a regexp.MustCompile parsing error?

Question

It fails for go run or go test (compile then run), but not for go build (compile only). I would have thought MustCompile relates to compilation, not runtime.

package main

import (
    "regexp"
)

var someInvalidRegex = regexp.MustCompile(`(?!`)

func main() {
    someInvalidRegex.MatchString("foo")
}

Runtime fail:

$ go run main.go
panic: regexp: Compile(`(?!`): error parsing regexp: invalid or unsupported Perl syntax: `(?!`

goroutine 1 [running]:
regexp.MustCompile(0x10b7d19, 0x3, 0xc420022070)
    /usr/local/Cellar/go/1.10.3/libexec/src/regexp/regexp.go:240 +0x171
exit status 2

Compilation success:

$ go build -o foo
$ echo $?
0

Runtime fail again:

$ ./foo
panic: regexp: Compile(`(?!`): error parsing regexp: invalid or unsupported Perl syntax: `(?!`

goroutine 1 [running]:
regexp.MustCompile(0x10b7d19, 0x3, 0xc420022070)
    /usr/local/Cellar/go/1.10.3/libexec/src/regexp/regexp.go:240 +0x171

Regex compilation happens at runtime. – Adrian Jul 31 '18 at 15:01 — Adrian, Jul 31 '18 at 15:01

score 5 · Accepted Answer · answered Jul 31 '18 at 15:00

5

Compiler does not analyze your regular expression. It is done in runtime. "Compile" part of "MustCompile" function name stands for the compilation of the regular expression.

answered Jul 31 '18 at 15:00

Maxim

514
2
7

Why does go build succeed for a regexp.MustCompile parsing error?

1 Answers1