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// Copyright 2022 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.
package script
import (
"cmd/go/internal/imports"
"fmt"
"os"
"runtime"
"sync"
)
// DefaultConds returns a set of broadly useful script conditions.
//
// Run the 'help' command within a script engine to view a list of the available
// conditions.
func DefaultConds() map[string]Cond {
conds := make(map[string]Cond)
conds["GOOS"] = PrefixCondition(
"runtime.GOOS == <suffix>",
func(_ *State, suffix string) (bool, error) {
if suffix == runtime.GOOS {
return true, nil
}
if _, ok := imports.KnownOS[suffix]; !ok {
return false, fmt.Errorf("unrecognized GOOS %q", suffix)
}
return false, nil
})
conds["GOARCH"] = PrefixCondition(
"runtime.GOARCH == <suffix>",
func(_ *State, suffix string) (bool, error) {
if suffix == runtime.GOARCH {
return true, nil
}
if _, ok := imports.KnownArch[suffix]; !ok {
return false, fmt.Errorf("unrecognized GOOS %q", suffix)
}
return false, nil
})
conds["compiler"] = PrefixCondition(
"runtime.Compiler == <suffix>",
func(_ *State, suffix string) (bool, error) {
if suffix == runtime.Compiler {
return true, nil
}
switch suffix {
case "gc", "gccgo":
return false, nil
default:
return false, fmt.Errorf("unrecognized compiler %q", suffix)
}
})
conds["root"] = BoolCondition("os.Geteuid() == 0", os.Geteuid() == 0)
return conds
}
// Condition returns a Cond with the given summary and evaluation function.
func Condition(summary string, eval func(*State) (bool, error)) Cond {
return &funcCond{eval: eval, usage: CondUsage{Summary: summary}}
}
type funcCond struct {
eval func(*State) (bool, error)
usage CondUsage
}
func (c *funcCond) Usage() *CondUsage { return &c.usage }
func (c *funcCond) Eval(s *State, suffix string) (bool, error) {
if suffix != "" {
return false, ErrUsage
}
return c.eval(s)
}
// PrefixCondition returns a Cond with the given summary and evaluation function.
func PrefixCondition(summary string, eval func(*State, string) (bool, error)) Cond {
return &prefixCond{eval: eval, usage: CondUsage{Summary: summary, Prefix: true}}
}
type prefixCond struct {
eval func(*State, string) (bool, error)
usage CondUsage
}
func (c *prefixCond) Usage() *CondUsage { return &c.usage }
func (c *prefixCond) Eval(s *State, suffix string) (bool, error) {
return c.eval(s, suffix)
}
// BoolCondition returns a Cond with the given truth value and summary.
// The Cond rejects the use of condition suffixes.
func BoolCondition(summary string, v bool) Cond {
return &boolCond{v: v, usage: CondUsage{Summary: summary}}
}
type boolCond struct {
v bool
usage CondUsage
}
func (b *boolCond) Usage() *CondUsage { return &b.usage }
func (b *boolCond) Eval(s *State, suffix string) (bool, error) {
if suffix != "" {
return false, ErrUsage
}
return b.v, nil
}
// OnceCondition returns a Cond that calls eval the first time the condition is
// evaluated. Future calls reuse the same result.
//
// The eval function is not passed a *State because the condition is cached
// across all execution states and must not vary by state.
func OnceCondition(summary string, eval func() (bool, error)) Cond {
return &onceCond{eval: eval, usage: CondUsage{Summary: summary}}
}
type onceCond struct {
once sync.Once
v bool
err error
eval func() (bool, error)
usage CondUsage
}
func (l *onceCond) Usage() *CondUsage { return &l.usage }
func (l *onceCond) Eval(s *State, suffix string) (bool, error) {
if suffix != "" {
return false, ErrUsage
}
l.once.Do(func() { l.v, l.err = l.eval() })
return l.v, l.err
}
// CachedCondition is like Condition but only calls eval the first time the
// condition is evaluated for a given suffix.
// Future calls with the same suffix reuse the earlier result.
//
// The eval function is not passed a *State because the condition is cached
// across all execution states and must not vary by state.
func CachedCondition(summary string, eval func(string) (bool, error)) Cond {
return &cachedCond{eval: eval, usage: CondUsage{Summary: summary, Prefix: true}}
}
type cachedCond struct {
m sync.Map
eval func(string) (bool, error)
usage CondUsage
}
func (c *cachedCond) Usage() *CondUsage { return &c.usage }
func (c *cachedCond) Eval(_ *State, suffix string) (bool, error) {
for {
var ready chan struct{}
v, loaded := c.m.Load(suffix)
if !loaded {
ready = make(chan struct{})
v, loaded = c.m.LoadOrStore(suffix, (<-chan struct{})(ready))
if !loaded {
inPanic := true
defer func() {
if inPanic {
c.m.Delete(suffix)
}
close(ready)
}()
b, err := c.eval(suffix)
inPanic = false
if err == nil {
c.m.Store(suffix, b)
return b, nil
} else {
c.m.Store(suffix, err)
return false, err
}
}
}
switch v := v.(type) {
case bool:
return v, nil
case error:
return false, v
case <-chan struct{}:
<-v
}
}
}
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