go const7 源码
golang const7 代码
文件路径：/test/const7.go
// run
// Copyright 2021 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Check that the compiler refuses excessively long constants.
package main
import (
"bytes"
"fmt"
"io/ioutil"
"log"
"os"
"os/exec"
"path/filepath"
"runtime"
"strings"
)
// testProg creates a package called name, with path dir/name.go,
// which declares an untyped constant of the given length.
// testProg compiles this package and checks for the absence or
// presence of a constant literal error.
func testProg(dir, name string, length int, ok bool) {
var buf bytes.Buffer
fmt.Fprintf(&buf,
"package %s; const _ = %s // %d digits",
name, strings.Repeat("9", length), length,
)
filename := filepath.Join(dir, fmt.Sprintf("%s.go", name))
if err := os.WriteFile(filename, buf.Bytes(), 0666); err != nil {
log.Fatal(err)
}
cmd := exec.Command("go", "tool", "compile", "-p=p", filename)
cmd.Dir = dir
output, err := cmd.CombinedOutput()
if ok {
// no error expected
if err != nil {
log.Fatalf("%s: compile failed unexpectedly: %v", name, err)
}
return
}
// error expected
if err == nil {
log.Fatalf("%s: compile succeeded unexpectedly", name)
}
if !bytes.Contains(output, []byte("excessively long constant")) {
log.Fatalf("%s: wrong compiler error message:\n%s\n", name, output)
}
}
func main() {
if runtime.GOOS == "js" || runtime.Compiler != "gc" {
return
}
dir, err := ioutil.TempDir("", "const7_")
if err != nil {
log.Fatalf("creating temp dir: %v\n", err)
}
defer os.RemoveAll(dir)
const limit = 10000 // compiler-internal constant length limit
testProg(dir, "x1", limit, true)
testProg(dir, "x2", limit+1, false)
}
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